1994_Maxim_Battery_Management_and_DC DC_Converter_Circuit_Collection 1994 Maxim Battery Management And DC Converter Circuit Collection

User Manual: 1994_Maxim_Battery_Management_and_DC-DC_Converter_Circuit_Collection

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Battery Management and
DC·DC Converter Circuit Collection
A Power-Supply Applications Guide
for Portable Equipment

Maxim Wishes to Acknowledge the Contributions of
Bruce D. Moore
and the
Maxim Applications Engineering Group

GeHing APplications Assistance, I.iterature, Samples
Applications assistance, literature, free samples, evaluation kits, and small production quantities can all be ordered
from Ma? 2.0V) unless noted. Detailed min/max specifications for all parameters can be
found in the deVice data sheets.

AIIIIAXIAIIII - - - - - - - - - - - - - - - - - - - - - - - -

iii

_ _ _ _ _ _ _ _ _ _ _ _ _ _ Table of Contents
Alphanumeric Index of Devices .•.•...•.....•••......•..•.••.••......•...•.•...•.••....•.•..•.vii
Section 1: NiCd/NiMH Fast Battery Chargers ........................................... 1
Simple Fast Charger with Linear Regulator Current Source ..........................................................................2
Simple Fast Charger with Buck Switch-Mode Current Source .......................................................................3
Microprocessor-Controlled Switch-Mode Current Source: A System Solution ............................................ .4
High-Voltage Buck Switch-Mode Charger .....................................................................................................5

Section 2: Main Power Supplies tor Low· Voltage Batteries
(4 cells and below) .....•..•...•..•..•..•.•.....•..•.•.....•...••....•.•.•..............••.......•.••••. 7
1-4 Cells to 3.3V/5V via Low-Power Boost Regulator .....................................................................................8
2-3 Cells to 5V at High Power: Parallel-Connected Dual Boost Controller ................................................... 9
2-3 Cells to 3.3V/5V at Medium Power ......................................................................................................... 10
2-3 Cells to 3.3V/5V and 5V/12V at Medium Power ..................................................................................... 11
2-3 Cells to 3.3V/5V, 12V, and -18V: A System Solution ............................................................................. 12
2-3 Cells to 5V at Low Power via PWM Boost Regulator .............................................................................. 13
2-3 Cells to 5V at Micro Power ..................................................................................................................... 14
3 Cells to 3V/3.3V at Medium Power via Low-Dropout PFET Linear Regulator ............................................ 15
4-6 Cells to 3.3V at Low Power via Buck Regulator ..................................................................................... 16

Section 3: 4-Cell to 5V Conve,'fers ••••••••••••••••.••••••••••••••••••••••••••••••••••••••••• 19
4
4
4
4
4

Cells to
Cells to
Cells to
Cells to
Cells to

5V via Boost/Step-Down Regulator .............................................................................................. 20
5V via Low-Dropout Linear Regulator ..........................................................................................21
5V via Boost with Diode Step-Down ............................................................................................. 22
5V via Inverter or Flyback .............................................................................................................23
5V via Step-Up/Step-Down Switchable Topology ........................................................................ 24

Section 4: Main Power Supplies tor High. Voltage Batteries
(5 cells and above} .........•.•..•.....•.....••.•....•.....•..•.•.••...•....•......••....•..••......•.25
5 Cells to 5V via Low-Dropout PFET Linear Regulator ................................................................................. 26
5 Cells to 5V and Multiple Outputs via Low-Dropout PNP Linear Regulators .............................................. 27
5 Cells to 5V via Low-Dropout, Low-Power PWM Buck Regulator ...............................................................28
6 Cells or 9V Transistor Radio Battery to 5V/3.3V at Low Power ..................................................................29
5-12 Cells to 3.3V at High Power ..................................................................................................................30
6-12 Cells to 5V at High Power .....................................................................................................................31
6-8 Cells to 3.3V/5V at Medium Power .........................................................................................................32
6-8 Cells to 5V via Negative Buck Topology ................................................................................................33
5-8 Cells to 3.3V and 12V at High Power: Buck Controller with Battery Charger .......................................34
6-12 Cells to 3.3V, 5V, and 12V at High Power ............................................................................................36
48V Subscriber-Line Telecom Power Supply ...............................................................................................38

Section 5: 3V·to-5V and 5V·to-3V Main Power Supplies .........................39
3.3V to 5V
3.3V to 5V
3.3V to 5V
5V to 3.3V
5V to 3.3V

at High Power ..............................................................................................................................40
at Low Power ...............................................................................................................................41
and 12V: Dual-Output Boost Controller ......................................................... ,........................... 42
at High Power ..............................................................................................................................43
at Low Power ...............................................................................................................................44

v

_ _ _ _ _~ _ _ _ _ _ _ _ _ Table of Contents
Section 6: Display Circuits - LCD Contrast and CCFT Supplies .•...•...••45
LCD Contrast with Digitally Adjusted Negative Output .............................................................................. ,,46
LCD Contrast, 5V to Negative Output via Autotransformer ..........................................................................47
LCD Contrast, 5V to Negative Output at Micro Power .................................................................................48
LCD Contrast, 4-8 Cells to Negative Output via Charge Pump ...................................................................49
LCD Contrast, 5-8 Cells to Positive Output ..................................................................................................50
CCFT Backlight Inverter with Current-Fed Royer Oscillator .........................................................................51
LCD Contrast and CCFT Power, 6-8 Cells System Solution .........................................................................52

Section 7: -5V Generators ......••.•...•••.•...••....•.•.•.•...•.•.......•.••....••..•.....•.•..•55
-5V from
-5V from
-5V from
-5V from
-5V from
-5V from

5V or 4-8 Cells at High Power ........................................................................................................56
5V or 5-8 Cells at Medium Power ..................................................................................................57
5V at Medium Power .....................................................................................................................58
5V at Low Power via Inverting Regulator ......................................................................................59
5V at Low Power via Charge Pump ...............................................................................................60
5V at Micro Power via Charge Pump ...........................................................................................61

Section 8: Flash Memory, PCMCIA, and Other 1.2V Power Supplies ...••. 63
5V to 12V at 30m A via Charge Pump ...........................................................................................................64
5V to 12V at 120mA ......................................................................................................................................65
5V to 12V at 500mA ......................................................................................................................................66
5V to 12V with Micropower Shutdown Mode ................................................................................................67
3.3V to 12V at BOmA .....................................................................................................................................68
2-3 Cells to 12V at 60mA ..............................................................................................................................69
PCMCIA Power Switching Network ..............................................................................................................70

Section 9: Miscellaneous Circuifs .......................................................... 73
Low-Dropout Linear Regulator with Diode OR'ed Output ...........................................................................74
High-Side Current-Sense Amplifier ..............................................................................................................75
N-Channel High-Side Power Switches .........................................................................................................76
System Voltage Monitor ................................................................................................................................77

Appendix A: Switch-Mode Design Equations .......................................... 79
Appendix 8: Abbreviation Glossary .••..••••.•...••.••......•.•.•........•......•..•••.....87
Appendix C: Sul1face-Mount Component Suppliers •.•....•.•.•.•...•.•..••••.•.•..• 89
Appendix D: Power-Supply Product Selection Guide ••••••••••••••••••••••••••••• 91
Appendix E: E"a/uation

~it

Ol1fering TClfJ/e •••••••••••••••••••••••••••••••••••••••.••••• 99

Appendix F: New Releases ....•.••.•.....••..•••....•.•.........•.•...........•....••.......•• 101
Appendix G: Fufure Products .•...........•....•.........................•..••....•.......... 1,11

vi

--------------------------------------------------~~)(I~

_________Alphanumeric Index 01 Devices
ICL7611
ICL7612
MAX620
MAX630
MAX634
MAX638
MAX639
MAX641
MAX660
MAX662
MAX666
MAX667
MAX713
MAX714
MAX718
MAX721
MAX722
MAX724
MAX730A
MAX731
MAX732
MAX734
MAX735
MAX738A
MAX739
MAX741
MAX749
MAX750A
MAX751
MAX752
MAX753
MAX754
MAX756
MAX759
MAX763A
MAX778
MAX780
MAX781
MAX782
MAX786
MAX872
MAX877
MAX 1044
MAX8213
MAX8214

.MAX•.M

Micropower Op Amp ............................................................................................................. 15,26
Micropower Op Amp ................................................................................................................... 75
High-Side Charge Pump ............................................................................................................. 76
Boost Regulator ........................................................................................................................... 14
Inverting Regulator ................................................................................................................ 48, 49
Buck Regulator ............................................................................................................................ 38
Buck Regulator .......................................................................................................... 17,24,29,59
Boost Controller ......................................................................................................................... 50
100mA Charge Pump .................................................................................................................. 60
12V Charge Pump ....................................................................................................................... 64
Linear Regulator ...........................................................................................................................74
Linear Regulator .......................................................................................................................... 21
Battery Charger ..................................................................................................................... 2, 3, 6
Subnotebook Supply ....................................................................................................................27
Palmtop SMPS........ .......................................................... .................................. ........ 9, 11, 42, 69
Boost Controller ........................................................................................................................... 66
Palmtop SMPS .. ,.......................................................................................................................... 12
Buck Regulator .............................................................................................................................. 6
Buck Regulator ............................................................................................................................ 28
Boost Regulator ........................................................................................................................... 41
12V Boost Regulator ................................................................................................................... 65
12V Boost Regulator ..................................................................................................12, 65, 67, 68
Inverting Regulator ...................................................................................................................... 58
BuckHegulator ............................................................. ;.............................................................. 32
Inverting Regulator ................................................................................................................ 23, 57
Universal Controller ............................................................................................................... 40, 56
Negative Output Controller ......................................................................................................... 46
Buck Regulator ...................................................................................................................... 16,17
Boost Regulator ........................................................................................................................... 13
Boost Regulator ..................................................................................................................... 33, 51
CCFT Supply ............................................................................................................................... 52
CCFT Supply ............................................................................................................................... 52
Boost Regulator ..................................................................................................................... 10,22
Inverting Regulator ......................................................................................,............................... 47
Buck Regulator ............................................................................................................................ 44
Boost Regulator ............................................................................................................................. 8
PCMCIA Switch ........................................................................................................................... 70
Subnotebook SMPS ................................................................................................................. 4, 34
Notebook SMPS .......................................................................................................................... 36
Notebook SMPS .............................................................................................................. 30, 31, 43
Voltage Reference ................................................................................................................. 15, 26
BoosVStep-Down Regulator ........................................................................................................ 20
20mA Charge Pump .................................................................................................................... 61
Voltage Monitor ............................................................................................................................17
Voltage Monitor ........................................................................................,.................................. 77

vII

Section 1
Fast Battery Chargers
Battery charger circuits encompass a wide range of design approaches, depending on the battery
chemistry, source voltage, and power level. For example, a charger for two M-size cells in a
palmtop computer that is supplied from a 9V DC wall-cube adapter must necessarily be quite
different from the charger for a to-cell laptop computer connected directly to the AC main power.
The following battery-charger collection covers fast charging of nickel-cadmium (NiCd) and nickelmetal-hydride (NiMH) batteries from 5V to 40V DC sources.

Battery Charger Application Chart
Chemistry

Recommended Charging Method

Lead-Acid

Float voltage source with current-limited output. The float voltage should be set
at 2.35V to 2.45 V per cell (consult manufacturer). Many of the buck regulators
and linear regulators in the Main Power Supplies from High-Voltage
Batteries (5 cells and above) section can be adapted to this task.

NiCd and NiMH

Fast-charge: current source into battery with redundant charge-termination
methods.
Trickle-charge: current source at C/10 or less. This can be as simple as a
resistor in series with a voltage source.

Lithium-Ion

~~)(I~

Float voltage source similar to lead-acid charger. The float voltage should be
set at 4.1 V to 4.2V per cell (consult manufacturer).

__________________________________________________________

Simple Fast Charger with
Linear Regulator Current Source
_ _ _ _ _~App'ication Parameters
Input Voltage Range ........................ ... (BATT + 1V) to 20V
5VMin
Max Charging Current Capability ...... Limited only by Max PD
Supply Current (not charging) ............................51lA Max
Efficiency ...... ............................. Approximately Equal to
VBATTNsOURCE x 100%

1.0

g
f-

z
w

0.8

..

0.6

a:
a:

:::>

u
0

9

en

:3
c.. 0.4

• Powers load and charges battery simultaneouslyeliminates battery switchover circuitry

'"c;;z

.

a: 0.2

• Small and low cost -16-pin SO package

:I:
U

• Charges 1 to 16 series cells
10

• Evaluation kit available

________Re'ated Data Sheet

15

20

VIN - VOUT DIFFERENTIAL (V)

Figure I. MAX713/MJD2955 Operating Area

• MAX713 Battery Charger
MJD2955 (DPAK)

_______App'ication Discussion
Two closely related problems found in powering small
portable systems are charging the battery and switching
over from battery power to AC power when an external
AC-DC adapter is plugged in. The following circuit
solves both problems at once with a low-cost linear
regulator approach that simultaneously supplies both
battery and load.
The fast-charge controller IC used here can supply the
system load current while the battery is being charged
by sensing and dynamically regulating the battery
current. The MAX713 terminates the fast-charge cycle
upon one (or all) of the following conditions: negative
delta-V sensing, thermistor temperature, clocked timeout, or voltage ceiling. The MAX713 can be configured
to drive a linear regulator, as in this example, or it can
gate an external switching-regulator current source as in
the following examples. The sister part, MAX712, is
identical except that it terminates the fast charge at zero
delta-V slope, which may be appropriate for certain
NiMH batteries.
Employing a linear regulator instead of a switching
regulator as the charger's current-source section is an
excellent approach for small systems such as palmtop
computers having low-voltage AC-DC adapters (5V-, 9V,
and 12V-output are common examples) and lowwattage battery packs. The linear regulator approach is
also effective for battery-backup in non-portable
systems (such as large file servers).
The decision to use a linear or a switcher usually hinges
on the level of acceptable power diSSipation in the linear
regulator pass element. For example, fast-charging three

- 1__~---'------~

FROM

r---~

+

SOU~10~F

lN4001

14
DRV VLlMIT 1

16
15 V+ AUXINIREF
MA)m3

7

TEMP
BATT+.t-2- - - .

5 THI

+

TO
LOAD

r-

10~FT

GND 13

+

-=-

RSENSE
O.25!l

Note: See the MAX712/MAX713 data sheet for additional pin-strap connections
to program the number of cells and the timer (PGO-PG3).

Figure 2. NiCd/NiMH Charger with Linear Regulator

750mA/hour NiCd cells from 9V DC at a 1C rate results
in a worst-case dissipation of about five watts- a little
too toasty for some hand-held applications. However,
keep in mind that the output impedance of most wallcube AC adapters will cause their output voltage to fall
under heavy load, thus reducing the load power; often,
this means that a wall cube that at first glance appears
to have too high an output voltage for the linear regulator
approach may actually be acceptable.

2 ________________________________

AlAXIAI

Simple Fast Charger with
Buck Switch-Mode Current Source
______,Appllcation Parameters
Input Voltage Range ......................... (BATT + 1.5V) to 20V
7VMln.
Max Charging Current Capability ....................3A as shown
Efficiency (VIN = 12V, 2 cells, 1A) ••••••••••••••••••••••••••••• BO%
• Includes step-down swltch-mode current source
• Charges 1 to 8 series cells
• Configurable Output Current

o

_ _ _ _ _ _ _ _Related Data Sheet

5
10
15
VIN·VOur DIFFERENTiAl M

• MAX713 Battery Charger

_______,Application Discussion
Fast-charging large batteries in compact enclosureSwhere heatsinking is impractical-raises the issue of
temperature rise. The battery-charger current source must
have high enough efficiency to prevent excess temperature
rise. However, cost is also important, so drastic measures
to improve efficiency (such as a synchronous rectifier)
usually aren't needed.
The current-source buck regulator shown here consists
of the buck switcher components (PFET, inductor, and
rectifier), the error amplifier within the MAX713, and the
resistor-capacitor network attached to CC. Other than
improved efficiency, the main difference between this
circuit and the linear regulator approach is that the linear
approach can service the load while simultaneously
charging the battery.
The control loop is a variable-frequency, hysteretic type
that senses and regulates the current through the
battery. Battery current is measured by the 0.08n sense
resistor. This sense signal is compared to an internally
generated 250mV threshold; the difference is gained up
by a factor of eight, and the resultant error signal
appears at the current-sense amplifier output (CC pin). A
second high-gain stage between CC and DRV compares
the error signal to the MAX713's +2.00V reference and
turns the PFET switch either on or off in order to regulate
the battery current. The circuit operates as a switcher
rather than a linear regulator due to hysteresis introduced
by the feedback divider and 33pF capacitor connected
to CC. The capacitor injects charge into the CC node
each time the PFET turns on or off, which kicks the error
Signal slightly above or below the +2.00V reference. This
action overdrives the second gain stage and ensures a
fast-switching drive signal to the PFET.
The circuit as shown is good for 3A charging currents.
Lower currents allow smaller external components; for
example, for a 1A charger, 1N5818s (1A Schottky) can
be substituted for the1N5821s, and a Sumida CD75-470
(47J.lH at 1A) SMT inductor can be substituted for the
Gowanda part. Also, higher input voltages can be
~A)(I~

20

Figure 3. MAX713 Buck Operating Area

11
5D¢i

INPUT7V

I

+
471lF

1N5821

2k

390n

O.SW

FAST
CHARGE

1.51<

~

14
DRV

1N5821

-=

33pF

15 V+

THI
PGMIl

AIAXI.M
MAX713

CC 11

8 FASTCHG
16 REF
1 VUMIT

BATT+ 2

7 TEMP

_+ 2x

1¢

+

NlCdOR
NiMH
(AS SHOWN)

0.0110

-=
Figure 4. NiCdlNiMH Charger with Buck Regulator

accommodated by adding a level-shifter between DRV
and the PFET driver transistors, and changing the 390n
shunt regulator resistor value.

____________________________________

3

Microprocessor-Controlled Switch-Mode
Current Source: A System Solution
______Application Parameters
Input Voltage Range ....................................... 5V to 18V
Quiescent Supply Current (VIN = 5V) ..........................1mA
Max Load Current Capability (VIN = 5V) .... 1.5A (configurable)
• 3.3V current-mode PWM buck controller
• 15V (12V) flyback controller
• Battery charger current source (buck SMPS)
• Dual PCMCIA Vpp outputs (OVNCcJ12V)
• 300kHz fixed-frequency oscillator
• 10llA shutdown mode

100

VIN= 6V

90

~ 70
><.>
15 60
C3

~

50
40
30

3.3V
BUCK OUTPUT

~

20
lmA

• 2.5V 1.5% reference output
• 5V low-dropout linear regulator output

VIN = 15V

/.

80

Figure 5. Efficiency

VS.

lOrnA

1111

111111111

n[

111Jl111

100mA
lA
LOAD CURRENT

lOA

Load Current

• Analog multiplexer
• Five level translators for high-side switching
• SPI-compatible serial interface
• Evaluation kit available

_ _ _ _ _ _ _ _ Related Data Sheet
• MAX781 Subnotebook SMPS

_______,Application Discussion
One effective scheme for fast-charging batteries is to
employ a microcontroller with on-board ADC as the
charger intelligence. This approach allows the charging
algorithm to be changed easily through software. In this
situation, a "dumb" switching regulator current source is
needed, preferably one that has a digitally adjustable
charging rate (to accommodate different battery packs).
The circuit shown here integrates a switching regulator
current source with several other power-supply
functions. The current source output is programmed
through a 3-wire SPI-type serial interface. See page 34
for further discussion.
A stand-alone buck regulator current source can be
fashioned from the MAX724 circuitry used in the
following application (High-Voltage Buck Switch-Mode
Charger).

4 ________________________________

.JM.AXI.JM

Microprocessor-Controlled Switch-Mode
Current Source: A System Solution

BATTERY
CHARGER
DC INPUT

ANALOG MUX I/O
,------...-...,

~-----'--1%

VREF OUTPUT

2 4 33 31
29 AOUT AUXIN TEMP VREF
VCHG
VL "ln8~~--+-~+~- +5V OUTPUT
1N4148
::r::: 4.7~F

+

T.
47J.lF =
03

DCHG

=

AVPP h-r-.~-t---- }
BVPP

17-I-t~+---

.A'lAXI.A'I
MAX781 VDD 6
28 V+

PCMCIA
VppOUTPUTS

+15V
. -__--+--~~O=UTPUT

DHI
+3.3V
OUTPUT

17 CSBAT
10~H

BST3

0.1n

T1

0.050

T

+

220J.lF

DL3
4100

IN~~~~~~E

SS3
16 COMP

{

I/O

CE
SCLl(
DIN
DOUT
INT

CS3
30UT
GD1
GD2
GD3
GD4
GD5

25
36

1

t;c----t;c-----

h---

GATE-DRIVER OUTPUTS
(FOR POWER SWITCHING)

OSCILLATOR _ _---><..j
SYNCHRONIZAnON
01, 02 = Si9956DY
03 = Si9405DY
T1 = SAE POWER INC 116026
4:1 TURNS RATIO

Figure 6. Single-Chip Subnotebook Computer Power Supply

~AJCI~

_____________________________________________________________

5

High-Voltage Buck Switch-Mode Charger
_ _ _ _ _~App/;cation Parameters
Input Voltage Range ......................... (BATT + 2.5V) to 40V
15V Min
Max Charging Current Capability ................................ 5A
Supply Current (not charging) ................................. 1OjJA
Efficiency (VIN = 20V, 1A, 6 cells) ............................. 80%
• Charges high-cell-count battery packs
• Powers load and charges battery simultaneouslyeliminates battery switchover circuitry
• Charges 1 to 12 series cells

o

10

20
30
INPUT VOLTAGE (V)

_ _ _ _ _ _ _ Re/ated Data Sheets
• MAX713 Battery Charger

40

Figure 7. MAX713/MAX724 Operating Area

• MAX724 Buck Regulator

_______Application Discussion
At high input voltages (15V and above), buck switching
regulators with internal bipolar NPN switches such as the
MAX724 become economical and relatively efficient,
since the large VCE (sat) voltage of the switch becomes
small relative to the input voltage. This circuit employs a
robust SA bipolar switching regulator IC that is
configured for current-source output. Maximum input
voltage is 40V.
The compensation (VC) pin of the MAX724, which is at
the internal junction of the error-amplifier output and the
PWM comparator input, is overdriven by an external op
amp that allows the MAX713 DRV pin to control duty
cycle. The MAX713 senses the battery charging current
and modulates the duty cycle in order to regulate the
charging current. The dominant pole for loop stability is
set at the compensation pin of the MAX713 (CC), so do
not increase the value of the battery filter capacitor
without also increasing the CC capacitor. Lower values
for both capacitors are preferred in order to maintain
good transient response characteristics.
This circuit is configured to supply a load while
simultaneously charging the battery. If the drop across
the sense resistor during discharge is undesirable, the
resistor can be shorted out temporarily with an optional
low on-resistance (rDS (on» N-channel MOSFET. If load
transients are expected during the fast-charge cycle,
check the worst-case load step response. The battery
voltage must settle to SmV x N (where N is the number of
cells) in less than 2msec for the MAX713's internal
analog-to-digital converter to terminate the cycle
properly.
For applications needing 2A or less, using a MAX726
instead of the MAX724 provides somewhat better
efficiency due to its low-saturation, non-darlington switch.

INPUT
15VT040V

+-__--"15 VIN

SWj-'4_ _ _ _-.-_---,
.MAXUM

MAX724
MAX726

1

3
GNDF----,

FB

VC
2

1N5820

L1
100flH

lN5817

2k

lN5820

15 V+

1 VlIMIT

~

BATT+1"2--t---.
TO LOAD
+

_ BATTERY
(1 TO 8 CELLS
'--_ _ _ _ _-_--_-_~ AS SHOWN)

L1 = COILTRONICS CTX100-3

Figure 8. High- Voltage, High-Power DC Input Charger

6 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ -'MAXI-'M

Section 2
Main Power Supplies for Low Voltage Batteries
(4 cells and below)
The following circuits are DC-DC converters intended to generate the main system supply voltage
in battery-powered systems (usually 3.3V or 5V). The circuits are presented in order of increasing
battery voltage. Often, there will be more than one solution presented for each application niche,
providing alternate solutions that have unique performance advantages.
Most of the circuits in this first section covering low-voltage batteries are by necessity the simple
boost (step-up) topology in one form or another, although there are two 4-cell buck regulators at
the end. The next section deals with 4-cell to 5V converters, which are hybridized step-up and
step-down converters. The third section on main power supplies covers high-voltage circuits and
contains mostly buck (step-down) switching regulators plus a couple of low-dropout linear
regulators.

Control Schemes
There are three basic control schemes found in the DC-DC switching-regulator ICs in this collection:
•

Current-mode Pulse-Width Modulation (PWM)

•

Fixed-time Pulse-Frequency Modulation (PFM)

•

Current-limited Pulse-Frequency Modulation (PFM)

Design equations for each of the control schemes are found in Appendix A. Generally speaking,
the PWM ICs have higher quiescent supply current than the PFM ICs. In return, the PWM ICs
provide superior noise characteristics (usually important only in noise-sensitive applications such
as radios and cellular phones).

~~XI~

__________________________________________________________

7

1-4 Cells to 3.3V/5V via
Low-Power Boost Regulator
_ _ _ _ _--'Application Parameters
Input Voltage Range ......................................1V to 6.2V
Start-Up Supply Voltage (ILOAD = 0) .......................... O.9V
Quiescent Supply Current (VIN = 2.5V) ..................... 2201lA
Max Load Current Capability (VIN = 1V) ................... 100mA
(VIN = 1.8V) ................. 240mA

90

- ~~JII

80

e

70

w

60

~

50

G
z

?

.

C3

• Internal low VF rectifier
• Continues to regulate with VIN > VOUT

40

• Rectifier can be turned off-blocks inductor-diode
leakage path and completely disconnects load
from battery

!Iili

Vour= +3.3V
L1 =2211H

..

1111111 III

30
100J,lA

VIN

VINI11111

J..

• Withstands output short-circuit to ground
• Pulse-skipping PFM

f-'

1mA

10mA
100mA
LOAD CURRENT

1A

Figure 9. Efficiency vs. Load Current

• 20J..LA shutdown mode
• Adjustable switch current limit
• Adjustable output version

INPUT

• Evaluation kit available

_ _ _ _ _ _ _ _ Related Data Sheet
• MAxna Boost Regulator
100llfi

_______.Application Discussion
A single-cell battery, especially near end-of-life, barely
provides adequate gate-drive voltage to start up a
MOSFET-based switching regulator. If a single-cell
system must start up under load, a bipolar switching
transistor is a good alternative to MOSFETs, especially to
discrete power MOSFETs, the best of which today have
a very high 2V worst-case gate threshold voltage
specification.The MAX?77 overcornes this problem by
employing an internal NPN bipolar switch.
The MAX?77/MAX778/MAX779 are micropower step-up
converters built with a high-speed (200kHz) pulseskipping PFM controller. High operating frequency
allows the inductor to be made very small (1 OJ..LH or less),
reducing the needed energy storage and core size.
These ICs accept 1V to 6.2V (1-cell to 4-cell) inputs and
generate fixed 3V, 3.3V, 5V, or adjustable outputs. Each
replaces the usual external Schottky rectifier with an
internal active rectifier that completely turns off in
shutdown mode, entirely disconnecting the load from the
source, overcoming a fundamental problem of the boost
topology.

.MAXI.M
MAX778

+3.3V
'---t-_+--_......._=OUTPUT

L1 = SUMIDA CD54-220
L1 ( 1O~H. LOW PROFILE) = SUMIDA CDRH62-100

Figure 10. Single-Cell Boost Regulator with Synchronous Rectifier

The internal synchronous rectifier can also act like a lowdropout linear regulator. This switched linear mode
occurs automatically as the input voltage exceeds the
programmed output voltage, thus allowing for wider
input voltage ranges than are normally possible with a
simple boost regulator (for example, 4 cells in, +5V out ).

8 _______________________________

AII.AX.AII

2·3 Cells to 5V at High Power:
Parallel·Connected Dual Boost Controll~r
______,App'ication Parameters
Input Voltage Range ...................................O.9V to 5.5V
Start-Up Supply Voltage (I LOAD = D) ..........................1.4V
Quiescent Supply Current (VIN = 3V)
Low-Power Mode ............. HDIJA
High-Power Mode ........... .24DIJA
Max Load Current Capability (VIN = 3V) ...................... 1.5A

90
80

C
(;

i'ii
u

• Low-powerlhigh-power mode switch

~l]1tjf"

VVIN';;'2V;

.

70
60

~

-

VI~ ~ ~~

-:"'

--

I
I

50

• All surface-mount components
40

• Pulse-skipping PFM

/
100~

- - = LOW·POWER MODE
- - - - _. = HIGH·POWER MODE
1mA

• 1.5% reference output

10mA
100mA
LOAD CURRENT

1000mA

• Power-fail detection output
Figure 11. Efficiency vs. Load Current

_ _ _ _ _ _ _ _Re'ated Data Sheet
MAX718 Palmtop SMPS
INPUT

_______,App'ication Discussion
"High power" in the world of small 2-cell boost regulators
translates to a 5V at 1A output, which is just 5W. But
getting even 5W from a 2-cell or 3-cell battery is a nontrivial design problem, Peak currents will be higher than
2A, which means that even small voltage drops in the
power devices, battery, capacitors, and PC board wiring
can result in grossly poor efficiency and outright failure.
For example, an AA alkaline battery pack can't support a
5W load at all, except in short surges, due to high
internal battery impedance. However, NiMH and NiCd
battery packs offer the low output impedance needed for
continuous heavy load drains.
This circuit connects two boost regulators from a MAX718
in parallel, and is intended to provide surge-current
capability for small systems with occasional heavy loads
(such as disc-drive motor spin-up or radio transmission).
The, main regulator contributes its good light-load
efficiency during normal system operation and guarantees
low-voltage start-up (its power MOSFET has a 0.8V gate
threshold voltage). The auxiliary regulator with external
MOSFET is not limited to 5W output; it can be tailored to
heavier loads with bigger inductors and capacitors.
Normally, paralleling unsynchronized switching regulator
outputs like this is a bad idea, due to possible beat
frequency problems between two close oscillator
frequencies and current "hogging." In this case, it works
because of the widely differing current capabilities and
totally asynchronous switching of the two regulator
sections. Light-load efficiency improves 10% when

AlAXIAI

C1
330~F

+

I

L2
HIGH-POWER!
LOW-POWER
MODE CONTROL
HP/LP

-=

10~
O.1~

1 BKUP

V+ 16

2 120N

LX 15

I-:l.

MAXIA4
3 3/5 MAXT18GNO 14

4 1215

+5V
OUTPUT

1N5B17
1N5B17

LIN 13

C2

01330~+

-=-

7 LXB

FB12 10

B FB3

Pfo9

0,10

I

01 = MT03055EL OR SILICONIX Si9410DY
C1. C2 = 330~. 6.3V SPRAGUE 595D SMT TANTALUM
L1= SUMIDA CD54-220 (22I'H)
L2 = SUMIDA CD105-100 (10I'H)

Figure 12, High-Power, Low-Voltage Boost Regulator

operating in low-power mode (200mA max load current)
instead of high-power mode, due to the reduced peakcurrent level.

9

2·3 Cells to 3. 3 V/5 V at Medium Power
______,Application Parameters
Input Voltage Range •.•••••••••••••••••••••••••.••••••• O.9V to VOUT
Start-Up Supply Voltage •...•........•..•.•..•••••••••••••••.••• 1.4V
Quiescent Supply Current (VIN = 3V)
3.3V Mode ••.•••.••••••••••••••••601lA
5V Mode •••••••••••••••••••••••• 1401lA
Max Load Current Capability (VIN =3V, 5V mode) ••••••• 400mA

90

V~~~~ill' ..... ,

80

/

VBATT = +2.5V

~ 70

VBATT= +1V

~

w

~

60

• O.5MHz switching frequency

VOUT= +5V

L1 i' ~2rrll

• Pulse-skipping PFM
• 1.5% reference output (alive in shutdown)

~ mill

40
l001lA

• Power-fail detection

lmA
lOrnA
LOAD CURRENT

100mA

• 20p,A shutdown mode
• Adjustable-output version available (MAX757)

Figure 13. Efficiency vs. Load Current

• Evaluation kit available
INPUT

_ _ _ _ _ _ _ _Related Data Sheet
• MAX756 Boost Regulator

L1
221lH

_______Application Discussion
Palmtop computers place tough design requirements on
the power supply: On one hand, they must be ultra-small
to fit into compact enclosures; on the other hand, they
must be efficient and have ultra-low standby currents to
provide battery life measured in days and weeks. Small
size means high frequencies for tiny inductor cores, but
high frequencies imply high switching losses and poor
efficiency. This circuit strikes a balance between size
and effiCiency by using a fast MOSFET switch coupled
with a PFM control loop that has judiciously chosen ONtime and OFF-time values.
This circuit and the two that follow are building blocks for
all kinds of medium-power palmtop applications. The
MAX756 shown here contains a O.4n N-channel
MOSFET switch that has a very low O.BV gate threshold
voltage - a feature that allows it to start up under heavy
load and low input voltage conditions. Other nice details
include a low-quiescent 1.5% accurate voltage reference
output and accurate low-battery detection.
Inductor values can be less than 10p,H with little effect on
supply current, making the MAX756 shine in size c
constrained applications such as PCMCIA memory
cards. Miniature (3mm diameter) inductors are made
possible by a relatively high O.5MHz maximum switching
frequency. While one might expect to pay the penalty of
increased supply current for O.5MHz operation, the

ON/OfF
8
1 SHDN
LX
(OFF IS < O.4V.
AIIAXIM
ON IS>1.6V)
MAX756
23j5
VOUT

LBI

LBO

lN58l7

3.3VI5V
OUTPUT
(SV AS SHOWN)

::r::+ lOOIlF
-=POWER-FAIL
OUTPUT
L1=SUMIDA CD54-220
L1 = (10~H. LOW PROFILE) =
SUMIDA CDRH62-100

Figure 14. 2-3 Cell Medium Power Boost Regulator

MAX756 draws only 60p,A, due to an advanced PFM
control scheme.
Low inductor values (5p,H to 22p,H) allow physically small
cores, with little penalty in reduced efficiency or output
current capability. High inductor values (>22p,H) allow
peak current levels to be kept low, reducing the
necessary filter and input capacitor sizes in lightly
loaded applications.

10 _ _ _ _ _ _ _ _ _ _~_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ AlAXIAI

2·3 Cells to 3.3V/5V and 5V/12V
at Medium Power
______ Application Parameters
Input Voltage Range ....... ........................... .O.9V to VOUT
Input Voltage Range (wall cube) ........................1V to 20V
Start-Up Supply Voltage (I LOAD =0) ..........................1.4V
Quiescent Supply Current (VIN = 3V)
Main SMPS = 5V ............ .. 140j.tA
Both SMPS ..................... 500j.tA
Max Load Current Capability (VIN =3V)
Main SMPS =5V ... ......... .. 400mA
Auxiliary SMPS = 12V ....... 120mA

90
80

e:

(;

70

~~

60
50

l/I.

V-~THmr-+++Hffir-~TH*H

11~Y-++t+fH+-H-H++Hl---+-++++f-Hl

40
'OO~A

• Dual regulated outputs

lmA
10mA
LOAD CURRENT

• Pulse-skipping PFM

100mA

• Accepts three input sources
• O.5MHz switching frequency

Figure 15. Efficiency vs. Load Current (5V Mode)

.1.5% reference output (alive in shutdown)
• Power-fail detection
• Evaluation kit available

MAIN BATTERY
INPUT

...,----.

--- --- --- - -- -- -- -- --- --- ----

_ _ _ _ _ _ _ _ Related Data Sheet
• MAX718 Palmtop SMPS

MAIN
OUTPUT -.........P:c1kt-.....-7"'i
3V15V

_______ Application Discussion
Size and cost constraints of PDAs and palmtop
computers necessitate higher levels of integration. The
following circuit shows a system-engineered IC that
integrates four control loops in a dual, low-voltage
switching regulator application.
This medium-power palmtop supply can generate 3.3V
and 5V, 3.3V and 12V, or 5V and 12V, depending on the
state of certain logic control inputs. Two regulated output
voltages are generated from one of three input voltage
sources: an AC-DC wall-cube adapter (7V to 20V), a
main 2- or 3-cell battery, or a lithium backup battery. The
dotted-line connection at the top of L2, which powers the
auxiliary supply, is normally hard-wired to the main
battery, but can also be connected to the main output
when power comes from the AC wall adapter. The main
switching regulator automatically shuts off to save the
batteries when the AC-OC wall cube is plugged in.
The two switch-mode supplies are the same type as
found in the MAX756, which has a wide range of
maximum switching frequencies. Practical inductor
values are from 5!lH to over 200!lH, allowing one to trade
off switching losses and physical size. Lower inductance

~AXI~

MAXLNI
7
MA)me
....-_._-I--__ CONTROL
BKUP 1

liDs

120N ...2f--_ _
1215 ...4f--_ _

Q1 = MOTOROLA MTD3055EL
OR 1/2 Si9942
L1. L2 = SUMIDA C054-220

Figure 16. Dual-Output Palmtop Power Supply: 5V/12V Version

values increase frequency without affecting peak
currents or load current capability significantly.
Inductance values can be increased for lightly-loaded
applications, in order to reduce peak currents.

11

2·3 Cells to 3.3V/Sv, 1211, and -18V:
A System Solution
______ Application Parameters
Input Voltage Range ...................................1.8V to 5.5V
Quiescent Supply Current (VIN =3V, 12V OFF) ...........350J,IA
Max Load Current Capability
VIN = 2V
VIN = 2.5V
+5V Output... ........................... 200mA
275mA
+12V Output .............................40mA
60mA
-18V Output. ............................................ Configurable
• Triple output

90
80

C
~

70

~

60

ffi
u

50

r- r--

V

......

I~ VV
/

1'\

~

~J1J

NJIII

11m
J'N'='~J

• PFM and PWM
40

• 5msec rise time (12V regulator, full load)

lmA

• 1.5% reference output (alive in shutdown)
• Power-fail detection comparator

10mA
LOAD CURRENT

100mA

Figure 17. Efficiency VS. Load Current (12V Regulator Only)

• Evaluation kit available (MAX722)

________Related Data Sheets
• MAX722 Palmtop SMPS
• MAX73412V Boost Regulator

_______.Application Discussion
The problem of inadequate gate-drive swing is often
encountered when designing low-voltage power
supplies. This circuit powers one of its switching
regulator ICs from a +5V bus generated by another
switching regulator IC to achieve gate-drive levels higher
than the battery voltage.
The dual-output MAX722 IC is the heart of this systemengineered power supply intended for ultra-small
palmtop-style computers. The main regulator uses a low-

threshold MOSFET to generate the 5V logic supply (3.3V
is also possible). The MAX722's inverter section
provides an adjustable negative bias voltage for LCD
contrast control. A MAX734 boost regulator chip
generates + 12V flash programming voltage for solidstate mass storage or PCMCIA memory cards.
The MAX734's power-supply pin, which draws little
current (1mA), is powered from the 5V system supply,
while the inductor connects directly to the battery. This
scheme provides good gate-drive levels to the
MAX734's internal MOSFET while avoiding the
compounded efficiency losses and extra loading that
would result from powering the inductor from the 5V
supply. If the main output is set at 3.3V, the MAX734 V+
pin should be bootstrapped (connect V+ to +12V
instead of +5V) for enhanced gate drive.

BATTERY INPUT
L1 = SUMIDA CD43-100
L2 = SUMIDA CD54-220
L3 =SUMIDA CD43-470

Ll
10j.il1
.5VOUTPUT
6 LX

4

v.

cc:X;;;;

lN4001

3300

FBN 1-"8'--_ _ _--'-~
LCD ONIOFF

+5VON/OFF

VREF 1-"5'--_ _ _ _"
~ O.22~F

POWER-FAIL OUTPUT

Rgure 18. Triple-Output Palmtop Power Supply

12 ______________________________________________

~~)(I~

2·3 Cells to 5V at Low Power via
PWM Boost Regulator
______App'ication Parameters
Input Voltage Range •.••...•..•....•.••...•.•••.•••..•...•.. 2V to 5V
Start-Up Supply Voltage (ILOAD = 0) .•.••..••..•.•••...•...... 1.2V
Quiescent Supply Current (VIN = 3V) .•.••••.•.••••••.••••.•.•. 2mA
Max Load Current Capability (VIN = 2.7V) ••..••••••••.•.• 1DDmA
• 170kHz fixed·,h"equency oscillator
• Current-mode PWM
• 30J.l,A shutdown mode
• 1.23V reference output

90

~VIN=4V

80

~

>u

70

~

60

iIi
u

IN = 2.5V

/'"

V
III

//

50

1

40

1mA

10mA
100mA 200mA
LOAD CURRENT

________ Re'ated Data Sheet
• MAX751 Boost Regulator

I II

/1-"

Figure 19. Efficiency VS. Load Current (Bootstrapped)

_______App'ication Discussion
In many portable products, such as cellular phones and
medical instruments, noise generated by switching
regulators is a major consideration. This circuit provides
a fixed-frequency PWM alternative to the pulse-skipping
control scheme usually found in low-voltage switching
regulator ICs. The trade-off for low-noise operation is
increased quiescent supply current and subsequent
lower efficiency at light loads.
The optional load-disconnect circuit breaks the parasitiC
path from input to output, allowing the output to go to OV.
In shutdown mode, there is less than O.6V difference
applied to the PNP's base-emitter junction. So, the PNP
turns off, breaking the inductor-diode path and
incidentally reducing supply current to less than 1J.IA (by
disconnecting the internal feedback resistor divider).
Note: See also the MAX7S1's big brother, the MAX731,
which has a bigger switch transistor and comes in a
larger package. Refer to the 3.3V to 5V at Low Power:
MAX731 Boost Regulator circuit for the schematic.

INPUT
ON/OFF
(OFF IS 2V)

11

1 SHDN

+
4.7 F

2 VREF

VOUT 7

AIAXIAII

SS MAX751 LXp6'--t_

__.f-_ _

O.1~F

+5V
OUTPUT

4 CC

L1 = SUMIDA CD54-220
INPUT

OPTIONAL
LOAD-DISCONN=.:EC;,;..T--::-_--,
CIRCUIT
-

AIAXIAII
MAX751 LX

..----<....f-_----'

VOUT

Q1 = ZETEX ZTX749 or 2N4403

Figure 20. 2-3 Cells to 5V with PWM Boost Regulator

"..AXI"..

13

2·3 Cells to 5V at Micro Power
______Application Parameters
Input Voltage Range ......................................1.6V to SV
Start-Up Supply Voltage (ILOAD =0) ................•...........2V
Quiescent Supply Current (VIN = 3V) .......................160jJA
Max Load Current Capability (VIN = 3V) ...................... SmA
• Pulse-skipping PFM
• Cost-effective
• 1J.1A shutdown mode
• Low-battery detection comparator

60

1t!W

50

C
G
z

I

40

w

(3

it

30

J

20
10

V
10~A

100~A

lmA
LOAD CURRENT

_ _ _ _ _ _ _ _Re/ated Data Sheet
• MAX630 Boost Regulator

lOrnA

Figure 21. Efficiency VS. Load Current

_______Application Discussion
Low cost is the main claim to fame of this flea-power
step-up regulator. It was included in this collection to fill a
need for the minimum possible solution to boost low input
voltages, and is most useful in situations where cost, not
efficiency, is the driving factor (although efficiency can be
improved by substituting a Schottky rectifier and lowresistance inductor).
Note: This circuit is bootstrapped; minimum start-up
supply voltage can be improved by applying the input
directly to +VS at the expense of low-voltage load current
capability.
The MAX630 employed here is the original micropower
DC-DC IC, first designed in 1983 for a scientific
calculator application. Although mature, the MAX630 is
still quite useful for boosting lithium backup batteries to
generate the regulated backup power needed by
pseudo-static RAM chips and many other lightly loaded
applications.
See also the MAX619 data sheet for an inductorless
charge-pump solution (a future product).

INPUT

ONiOFF
(OFF IS  1.8V)

6 IC

+VS "'5'------.-_---+

~

VFB "'7_-*-_---+

=

=

L1= INDUCTOR SUPPLY
LCM1812R-l02K
MOLDED CHIP INDUCTOR

Figure 22. Low-Power, Low-Cost Boost Regulator

14 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ .MAXI.M

3 Cells to 3V/3.3V at Medium Power via
Low-Dropout PFET Linear Regulator
______Application Parameters
Input Voltage Range ............. ..........................3V to 15V
Quiescent Supply Current (VIN = 6.5V, LP mode) .......... 40J,IA
(VIN = 6.5V, HP mode) ........ 750J,IA
Max Load Current Capability (VIN =6V, VOUT =3.3V) ...... .1A
(max load current is limited by power dissipation)

400

300

~

l-

S

200

0-

• Low dropout voltage: 100mVat ILOAD

a
II:
a

=1A

100

• Supply (ground) current is independent of load

Ql = Si9433DY

-

• 0.6% accurate reference output
..".....,.-

o

~

......V

200mA 400mA 600mA BOOmA
LOAD CURRENT

________ Related Data Sheets

lA

• ICL7611 Micropower Op Amp
Figure 23. Dropout Voltage VS. Load Current

• MAX872 Voltage Reference

_______,Application Discussion
See the discussion under 5 Cells to 5V via Low-Dropout
PFET Linear Regulator.
When this circuit is powered from a low voltage source
such as a 3-cell battery, make sure the PFET selected

has an adequately low gate-threshold voltage; for
example, the Si9433's rOS(ON) is guaranteed at VGS =
2.7V. See also the MAX682 data sheet (a future
product).

INPUT

lOOk

GND

lOOk

lOOk 1%

lOOk 1% (5V)
20k 1% (3V)

3V/5V
OUTPUT
Cl +
lOOIlF
LOW-ESR

I

MODE ,.,--;::~_-'\
SELECT HPtLP
HP MODE: lA MAX
LP MODE: 5mA MAX
01: SILICONIX Si9433DY OR SMD10P05L

Figure 24. Low-Dropout PFET Linear Regulator

~A)(I~

__________________________________

15

4·6 Cells to 3.3V at Low Power
via Buck Regulator
______Application Parameters

.c.im!i.1A
Input Voltage Range ...•.•••...•...• 4V to 11V
Quiescent Supply Current
(VIN = 4.8V, LP Mode) ••.••..•....•. 60J,IA
(VIN = 4.8V, HP Mode) .••.••..••.•1.6mA
Max Load Current Capability
(VIN = 4V, LP Mode) •.•...••.•....•• 10mA
(VIN = 4V, HP Mode) •...•••••••.••. 400mA
Efficiency at VIN = 4.8V
(ILOAD = 1mA, LP Mode) ••••.••••.. 72%
(ILOAD =100mA, HP Mode) ..•..••. 92%

.Gim!.ill
4Vto 11V
25J,IA
1.6mA
50mA
400mA
86%
92%

• 170kHz Fixed-Frequency Oscillator
• Current-Mode PWM or PFM
• Multiple Comparators for Battery Monitoring
• High-Power/Low-Power Mode Control

_ _ _ _ _ _ _Related Data Sheets
• MAX639 Buck Regulator
• MAX750 Buck Regulator
• MAX8213 Voltage Monitor

_______.Application Discussion
Small sUbnotebook-style systems often have very low
suspend-mode supply current drains, making hig.h
efficiency at light loads a desirable characteristic. At the
same time, on-board communication features' such as
radio modems make low-noise, fixed-frequency
operation desirable. These two circuits can both be
switched between a low-power PFM mode for suspendlevel loads and a high-power PWM mode for normal
system operation.
The MAX750A is a PWM buck regulator with internal
PFET switch that delivers 400mA load current at input
voltages as low as 4V (end-of-life of four NiCds). The
MAX750A can be used in conjunction with external
circuitry to improve light-load efficiency, as shown in the
following two circuits.
The first circuit (Figure 25) operates in a low-noise PWM
mode at high current levels, but can be switched into a
low-current pulse-skipping mode where the MAX750A is
disabled if the output is regulating properly. When
commanded by the LP/HP control input, this pulseskipping mode provides high efficiency at very light
loads due to reduced switching losses and lower
quiescent current consumption by the MAX750A. Note
that the MAX8213 quintuple voltage monitor chip, which
contributes an error comparator to regulate the output in
low-power mode, can be replaced with a single
comparator and inverter if desired.
A second circuit (Figure 26) is slightly more complex,
but provides extremely high light-load efficiency due to
the exceptionally low quiescent losses of the MAX639
PFM buck regulator chip. The MAX639 is essentially in
parallel with the MAX750A, driving the same inductor,
and when one chip is on the other is turned off.
Efficiency is 70% to 93% from 100J.lA to 400mA-a 400:1
load current range.

16 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

AI.AXIAI

4·6 Cells to 3.3Vat Low Power
via Buck Regulator
4Vlo l1V
INPUT

~____________________~1 SHDN

-+____,

~~B~____

r-------~-----'-I7 LX _VREFt-'2~____---,
GND MAX750A SS 3
VOUT
CC 4

EXTRA {
COMPARATORS
FORBATIERY
MONITORING

16 V
OUT2 13
8 DD.MAXIM
DIN MAX8213 IN1"3.---------,
12 OUT3
IN2
,----f-JlAIIv--...-+--._------_---------+- +3.3V OUTPUT
4 IN3+
AT400mA
5 IN3330pF
6 IN4+
7 IN4OUT4

LPlfiPCONTROL

Ll = SUMIDA CD105-101

CIRCUIT A
Figure 25. Skip-Mode PFMjPWM 3.3V Buck Regulator

470k

4VTO l1V
INPUT

. -_________8-1 SHDN

LBO 2

MAXIM

LP/HP
CONTROL

7
MAX639
.-------1-1 VFB
__
VOOi
.1-"---4------<>----*-----"-/ V'A...x.i,HDN 1
4
,'''-_ _ _ _~_--_I MAX750A ",2~_ _--,
GND
,r
LX
VREF......--~
GND
SS 3
SUPER LOW-POWER
4
REGULATOR TAKES OVER
-= 5 VOUT
CC
II
AT LOW OUTPUT CURRENTS lN5817
l1 100J!H
HIGH-POWER REGULATOR FOR
HIGH RUN-MODE CURRENTS
PFM
PWM
+3.3V OUTPUT
AT400mA
Rl
R2
R3

CIRCUIT B

L1= SUMIDA Col05-101

Figure 26. Micropower PFM/pWM Buck Regulator

17

Section 3
4-Cell to 5V Converters
Generating 5V from 4 series alkaline or zinc battery cells is a special case that places tough
requirements on the main DC-DC converter. The difficulty: The battery voltage ranges from 6.2V to
3.6\1, which is above and below the main output voltage, eliminating the simple and elegant buck
and boost topologies from consideration. The following circuits show four different ways to attack
the 4-cell problem.
See also the discussion under 6-12 Cells to 3.3V, Sv, and 12V at High Power for an inverter-plusbuck approach.

~~XI~

__________________________________________________________

19

4 Cells to 5V via
Boost/Step-Down Regulator
______Application Parameters
Input Voltage Range ...................................... 1V to 6.2V
Quiescent Supply Current (VIN =4V) .......................250~

90

VIN= 4V

Illili

V

(VIN = 6V) ........ ............... 320~
Max Load Current Capability (VIN = 2.5V to 6.2V) ....... 200mA

80

V

C

I

VIN= 6V

>u

15

70

I

(3

• Internal low VF rectifier

~

• Continues to regulate with VIN > VOUT

60

• Rectifier can be turned off - blocks inductor-diode
leakage path and completely disconnects load
from battery.

'/

50
100~A

• Withstands momentary output short-circuit to
ground
• Pulse-skipping PFM

lmA
lOrnA
LOAD CURRENT

100mA

Figure 27. Efficiency vs. Load Current

• Shutdown mode
• Adjustable switch current limit
• Adjustable-output and fixed 3.0V/3.3V
versions also available
INPUT

_ _ _ _ _ _ _ _ Related Data Sheet
• MAX877 Boost/Step-Down Regulator

_______ Application Discussion
This unusual switching regulator circuit is deceptively
simple in outward appearance. It is a boost regulator, but
contains an active rectifier in place of the usual external
Schottky diode. This active rectifier allows the MAX877 to
overcome many of the normal limitations of the simple
boost topology, such as lack of short-circuit protection,
lack of true shutdown (VOUT = OV), and the input voltage
range restriction VIN < VOUT '
The circuit operates in switch-mode even at high (VIN >
VOUT ) input voltages, with the active rectifier acting as
the switch. This action is more akin to a regulating
charge pump than to a buck regulator (buck mode
requires a second switch on the high side). Efficiency in
this mode approximates that of a linear regulator, which
is good over the 4-cell battery voltage range.
Output current limit (of the rectifier) is internally fixed at
1.6A. The low-side switch current limit can be set at 1A
by tying ILiM to V+, or reduced by adding a low-value
resistor between those pins. See also the MAX77? type,
which is very similar but intended for low-voltage
applications.

100!,F

r-'

I-=-

1L1

4T

31

2

GND AGND

Vt

11
ILiM

.MAXI.M
MAX877

22~

LX

VOUT

51

61

SAliN
7

FB

+3.3V
OUTPUT

81

lOOI'F

DN/OFF

~
-=-

L1 = SUMIDA CD54-220
L1 (10~H, LOW PROFILE) = SUMIDA CDRH62-100
Figure 28. 4 Cells to 5V: Boost Regulator with Dual-Purpose
Synchronous Rectifier

20 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

.hIAXI.hI

4 Cells to 5V via
Low-Dropout Linear Regulator
______App'ication Parameters
Input Voltage Range ....................................4V to 16.5V
Quiescent Supply Current (VIN = 6V) .........................10~
Max Load Current Capability (VIN = 6V) ................... 250mA
Dropout Voltage (ILOAO = 100mA) .......................... 100mV
Battery Life
(4 Alkaline AA at ILOAD =100mA,
to VOUT = 4.5V) .......................................11.2 Hours
Battery Life
(4 Alkaline AA at ILOAD = 100mA,
to VOUT = 4.75V) ....................................... 7.5 Hours

90
80

C

G

iij
C3

~

70

IIIII
yl~ i5V

/~

VIN = 6V

/1--"

60
50
40
30

-

Vlrm

100~A

1mA
10mA
LOAD CURRENT

• No magnetics
• Low-noise operation

100mA

Figure 29. Efficiency vs. Load Current

• 11lA shutdown mode
• Low-battery detect comparator

_ _ _ _ _ _ _ _ Related Data Sheet
JUT

• MAX667 Linear Regulator
.5V
OUTPUT

_______ App'ication Discussion
On the surface, a step-down linear regulator looks like a
poor choice for converting 4 cells to SV; when the output
stops regulating and the batteries go into the trash, a fair
amount of energy is still left in them. This wastefulness
seems just plain untidy from a pure engineering
standpoint. However, hard, cold test data indicates that
the linear regulator approach achieves good battery life
that can equal or even exceed some of the switching
regulator methods that follow. The success of the linear
regulator can be traced to the fact that its efficiency
becomes nearly 100% as the battery voltage nears SV.
Also, there are no pulsed currents as with switching
regulators; 12R losses and heat are therefore lower, so
the circuit is gentler to the battery chemistry compared to
a switching regulator. And while battery life doesn't
match the best switching regulator results, other benefits
of linear regulators (cost, size, low noise) still make them
attractive.
In general, switching regulator solutions provide a tightly
regulated output even at low battery Voltages. When the
output finally collapses, it does so rather abruptly (in
milliseconds). A linear regulator, on the other hand,
drops out slowly and gracefully as the battery voltage

~A)(I~

-1 DO

IN

.±L

2 OUT
LBO LNC
.MAXI.M
~ LBI MAX667 SET

-=-

~ GND

33"F
(LOW·ESR)I

-=-

SHDN

~

-

ON/OFF
(ON IS 1.5V)

Figure 30. 4 Celfs to 5V: Low-Dropout Linear Regulator

decays. This characteristic leads to a problem when
comparing linears to switchers: When do you call the
battery dead? The linear regulator solution typically
provides SO% additional life with a 4-cell battery if one
defines "dead" as VOUT = 4.SV instead of 4.7SV (see the
life test results in the table above).
The MAX667 linear regulator shown here works
extremely well in the 4-cell application due to its very low
dropout and extremely low quiescent current (10IlA).
See also the MAX682 data sheet for a PFET-based
solution (a future product).

________________________________________

21

4 Cells to 5V via
Boost Regulator with Diode Step-Down
______,App'ication Parameters
Input Voltage Range ••••••••••••.•••.•••...••••...•.••.... 2V to 6.2V
Start-Up Supply Voltage (I LOAD = 0) .•.......•..••..•.•....•.• 1.5V
Quiescent Supply Current (VIN = 5V) ......................... 701lA
Max Load Current Capability (VIN = 4V) ................... 400mA
Battery Life (4 Alkaline AA at ILOAD = 100mA) ......15.5 Hours

90

80

/

~

>u

ffi 70

U

• Battery voltage can go above or below output
voltage

VIN=4V
111111 I
VIN = 6V

,,-

~
60

/
I

• 55J.1A shutdown mode
50

• 1.25V ±1.5% reference output

100~A

lmA

10mA

100mA

LOAD CURRENT

________ Re'ated Data Sheet
• MAX756 Boost Regulator

Figure 31. Efficiency

_______.App'ication Discussion
Pre-regulating the input to a boost switcher is the overall
winner for the 4-cell application, since it retains the low
peak currents and uncomplicated circuit of the simple
boost topology. The basic idea is to boost the battery
voltage, once it falls below the desired output voltage,
until the battery is sucked dry. When the battery pack is
fresh, the switching regulator is disabled, so the worstcase high input voltage of 6.3V is dropped to S.4V by a
silicon rectifier in series with the normal Schottky boost
rectifier (a "cheap and dirty" equivalent to a linear
regulator). Note that there must be a minimum load of at
least O.SmA or so to prevent diode leakage current from
causing output overvoltage. The boost converter
operates until the batteries are less than 3V; efficiency is
typically 80% when the batteries are fresh, and is nearly
90% at V1N = 4V.
This diode-based circuit is conceptually similar to having
a linear pre-regulator for a boost regulator, and one can
easily substitute a linear regulator for the diode in order to
accommodate higher input voltages. Another similar
approach is to put the linear regulator at the output of a
boost regulator. Finally, if cost is key, one can always omit
the PFET switchover circuit, and include only the diode,
with some penalty in reduced battery life.

VS.

Load Current

INPUT

lN4001

ON/OFF

+5V
OUTPUT

(OFF IS  1.6V)

2 3/5
GND
AIIAXJAII

MAX 756

VREF

VOUT 1 " - - - - - - - '
LBI 5

L1= SUMIDA CD75-220

Figure 32. 4 Cells to 5V: Boast Regulator with Diode

22 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _~_ _

AIIIAXIAIII

4 Cells to 5V via
Inverter or Flyback
_ _ _ _ _Appllcat'on Parameters
Input Voltage Range .........•...•••••..••.•.•••••••.••.3.BV to 11V
Input Voltage Range (non-bootstrapped mode) •• 3.BV to 16.5V
Start-Up Supply Voltage (ILOAD = 0) ••..•.••••...•.••.•••. 4V Max
Quiescent Supply Currant (VIN = 5V) •...•.•••••.•••••••••.•1.BmA
Max Load Current Capability (VIN = 5V) ..•••..•••...•..••. 200mA
Battery Life (4 Alkaline AA atlLOAD =100mA) ...... 13.5 Hours

80

I

70

~

~

VIN~~V

60
50

• Battery voltage can go above or below output
voltage

40

• Works with any inverter

30

-

V

I

15
c:;

iii

/~

/1

~

I

VIN= 6V

V
lmA

lOrnA
100mA
LOAD CURRENT

• 165kHz fixed-frequency oscillator
• Current-mode PWM
• 1.23V reference output

Rgure 33. Efficiency vs. Load Current

• 1~A shutdown mode

_ _ _ _ _ _ _ _,RelatedData Sheet
• MAX739 Inverting Regulator

_ _ _ _ _ _,Application Discussion
Another tactic for combatting the 4-cell problem is
inverting the battery voltage (using a switch-mode
converter to create -5V) and moving the ground
reference of the circuit to the negative output. Having the
+5V output connected to the battery's negative terminal
in this manner may present a problem if other loads in
the circuit are referenced to the battery "ground" or if
additional voltages must be generated from the stack of
batteries. Also, the ratio of peak switch current to load
current in this circuit is relatively high (about two times
that of a boost regulator with the same output power),
necessitating a relatively big inductor core and
increasing 12R effiCiency losses. Finally, it requires a
high-side power switch (PNP or PFET) rather than a
more-attractive low-side switch (NPN or NFET). In spite
of these drawbacks, this circuit benefits many portable
equipment designs due to its simplicity and wide input
voltage range.
Flyback transformer and flying inductor solutions give
similar results in terms of battery life, due to efficiency
losses brought about by high peak currents that are in
turn caused by the high peak-current to average loadcurrent ratio of the inverting/flyback topology. In the
words of one disappointed flyback experimenter, "Nearly
beaten by a linear regulator, for crying out loud." In
defense of the flyback and inverter approaches, the input

~~)(I~

1.13.14
r-_-_--IV+

15011i' _+

1N5817

2 SHDN
A4AXIAI
5 SS MAX739VOUT 8

DRV-!-"9'---<1o.-+--l---'
+5V
OUTPUT

L1 = SUMIDA CD75-150

Figure 34. 4 Cells to 5V: Inverter with Battery-Referred Output

voltage range can be made very wide, with much better
efficiency at high input voltages than is possible with a
linear regulator. Wide voltage range is useful in situations
where the circuit must be able to accept alternate
battery packs, such as a 12V lead-acid battery (in
addition to a 4-cell NiCd or alkaline pack). In shutdown
mode the output goes to av, which is not automatically
the case for boost regulator approaches. And of course,
the flyback approach can generate isolated and multiple
output voltages by adding windings to the transformer.

____________________________________________________________

23

4 Cells to 5V via
Step-Up/Step-Down Switchable Topology
_ _ _ _ _---'Appllcation Parameters
Input Voltage Range ......................................3V to 6.5V
Quiescent Supply Current (VIN = 5.5V) •••••••••••••••••••••• 50IJA
Quiescent Supply Current (VIN = 4.5V) ••••••••••••••••••••• 110IJA
Max Load Current Capability (VIN = 3.75V) ••••••••••••••• 200mA
BaHery Lile (4 Alkaline AA at ILOAD =100mA) •••••• 17.2 Hours

100

Ullll

~ 80
~

iIi 70
U

~

60

• Battery voltage can go above or below output
voltage

50

• Pulse-skipping PFM

40

vi-'

VIN=3.5V

rII ,
~

l00pA

• Shutdown mode

I VIN= fN

L,...o

90

lmA

lOrnA

l00mA

LOAD CURRENT

_ _ _ _ _ _ _ _ Re'ated Data Sheet
• MAX639 Buck Regulator

_______App'ication Discussion
The ultimate weapon to date for taming 4-cell battery
packs this circuit switches from buck to boost mode as
the b~ttery falls below SV, but only requires a single
inductor. Switch-mode operation over the entire battery
voltage range allows for higher efficiency than the "boost
plus linear regulator" scheme, and avoids the high peak
currents and 12R losses of the inverting/flyback approach.
Efficiency is greater than 90% over nearly the entire.
battery range, extracting just about all the energy to be
had from a 4-cell pack. The trade-off for this high level of

Figure 35. Efficiency vs. Load Current

performance is more complex circuitry. Three power
MOSFETs are required (four if you parallel two P-channel
MOSFETs for lowest rOS(ON) as shown). Also, there is a
±2%change in output voltage as the battery voltage
reaches SV, required for the topology switchover function.
The low-battery detection comparator built into the
MAX639 Ie provides the step-up/step-down switchover
decision. The comparator monitors either the battery or
the output voltage. As the buck regulator goes into
dropout, the output begins to fall. As the output voltage
passes through 4.85V, the circuit switches from buck into
boost mode. and the output regulation point .shifts from
4.92V to 4.98V (nominal). If the output voltage rises above
S.1SV, the circuit switches back into buck mode.

SHUTDOWN CONTROL

lN4148

INPUT

ON/OFF

:.t

10k

510k

+

MAXJAII

lN4l48
lN4l48
lN4l48

220pF

1
MAX639 6
r--+---'f Vour
V+
2 U30
LX~5_++-...J

LBI

VFB

,..------1

+5V
OUTPUT

GND

470pF

lOOk

Figure 36. 4 Cells to 5V: Step-Up/Step-Down Switchable Topology

24 _

___________________________________

~----------------~x~

Section 4
Main Power Supplies for High-Voltage Batteries
(5 cells and above}
The following circuits are all step-down regulators intended for battery applications. They can be
put into three groups:
•

Linear regulators for 5 cells to 5V
ICL7611/MAX872 (3.3V also)
MAX714 Multi-output family

•

Stand-alone buck switching regulators
MAX730 PWM with internal PFET
MAX639 PFM with internal PFET
MAX786Idle-Mode™ PWM with external NFET
MAX738 PWM with internal PFET
MAX752 PWM with internal NFET
MAX638 PFM with internal PFET

•

Multiple Buck PWMs per IC (system-engineered)
MAX781 Idle-Mode PWM, 3.3V buck plus charger
MAX782 Idle-Mode PWM, triple-output

Like the low-voltage boost circuits, the step-down switchers are either current-mode PWMs or
straight PFMs. The three Idle-Mode circuits operate in PWM mode at moderate to heavy loads and
PFM at light loads (MAX786, MAX781, MAX782).
For high-voltage step-down needs in non-battery applications (distributed power supplies,
automotive, etc.), see the MAX724/MAX726 data sheet.

™ Idle-Mode is a trademark of Maxim Integrated Products.
~AXI~

_______________________________________________________

25

5 Cells to 5V via
Low-Dropout PFET Linear Regulator
______Application Parameters
Input Voltage Range .......................................3V to 15V
Quiescent Supply Current (VIN =6.5V, LP mode) ..........401JA
(VIN = 6.5V, HP mode) ........ 7501JA
Max Load Current Capability (VIN = 6V, Your = 5V) ........ .. 1A
(max load current is limited by power dissipation)

400

300

~

0-

S

200

Q.

a
a:
Q

• Low dropout voltage: 100mVat ILOAD = 1A

100

• Supply (ground) current is independent of load
• 0.6% accurate reference output

o
o

_ _ _ _ _ _ _ Related Data Sheets
• ICL7611 Micropower Op Amp
• MAX872 Voltage Reference

200mA 400mA 600mA aOOmA
LOAD CURRENT

Figure 37. Dropout Voltage

VS.

1A

Load Current
INPUT

_______,Application Discussion
NiCd and NiMH batteries have an end-of-life voltage of
almost exactly 1V per cell, making five series cells a
magic combination for generating SV with linear
regulators. If you neglect transistor base current and
quiescent losses, the efficiency of a linear regulator is
equal to VouTNIN, which approaches 100% as the inputoutput difference becomes small. When the batteries are
fresh (6V), theoretical efficiency is 83%. As the batteries
decay, the efficiency actually improves.
Although more expensive than a PNP transistor, a P-channel
MOSFET contributes no wasted power from base current
losses and has a lower saturation voltage at light loads than
a PNP. The use of readily available logic-level PFETs permits
incredibly low dropout voltages even at high load currents.
The low dropout characteristic of this circuit (100mV at 1A)
permits the system to "ride down" the battery voltage until the
output falls out of tolerance (Le., VOUT < 4.SV).
The ICL7611, with its pin-programmable bias current,
allows the circuit to be switched into a low-power (LP)
mode where the total supply current is less than SO!lA. In
this mode, the output is capable of supplying SmA for RTC
and RAM backup. In the high-power (HP) mode, up to 1A
output current is available. The input voltage range and
output current are limited by the external PFETs' package
power dissipation ratings; (VIN-VOUT)(IOUT) < 1.2SW unless
heat-sinking is provided.
The 1OO~F output capacitor was chosen for 1A maximum
load currents and may be scaled down for lighter loads if
desired. However, the lag compensation scheme used to
provide loop stability in this circuit depends on low
effective series resistance (ESR) for this capacitor. Be
sure that the loop zero 1/21tRESRC 1 occurs at a frequency
greater than 14kHz. When built with a low-ESR capacitor

VIN

lOOk

CaMP 6
AllAXlAII

MAX872
VOUT ",6-a...J\I'",

GND

lOOk

lOOk 1%

3V/5V
OUTPUT

lOOk 1% (5V)
20k 1% (3V)

Cl +
100J.LfI
LOW-ESR _

MODE ----==---.IIJ\.M
SELECT HPtiJi
HP MODE: lA MAX
LP MODE: 5mA MAX
01: SlliCONIX Si9433DY OR SMD10P05L

Figure 38. Low-Dropout PFET Linear Regulator

(1 OO~F with less than O. Hl ESR), AC load- and linetransient response are excellent, and phase margin is
better than 50 degrees under worst-case conditions.
The MAX872 low-power, low-dropout voltage reference
used in this circuit is accurate enough (0.6% over
temperature) to be valuable as a system reference,
See also the 4 Cells to 5V: MAX667 Low-Dropout Linear
Regulator circuit and the MAX682 data sheet (a future
product).

26 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

AtAXIAt

5 Cells to 5V and Multiple Outputs via
Low-Dropout PNP Linear Regulators
_ _ _ _ _~Application Parameters
Input Voltage Range ................................... S.OSV to 11V
Quiescent Supply Current (VIN =6V) ........................300IJA
Standby Supply Current (VIN =6V) ......................... 3SIJA
Max Load Currently Capability
(AUX OUT, VIN = 6V) .......... 1A Continuous

100

80

VIN: 6V

~

t

ffi

60

//

U

,...

~

• Output voltages: 5V at 1A (2A peak)
5Vat 100mA
-26V at 30mA for LCD

VIN: 10V

40

1/

• On-board DAC for LCD adjustment

20

lmA

• Power-fail and low-battery detect flags
• Lithium backup-battery switchover
• Linear and PFM switching regulators

VINI: r·~5V

/"

lOrnA
100mA
LOAD CURRENT

lA

Figure 39. Efficiency vs. Load Current, AUX Output

• Standby and backup modes

_ _ _ _ _ _ _ _ Related Data Sheet

INPUT

LCD CONTROL INPUTS
ON/OFF ADJUST

• MAX714 Subnotebook Supply
14
E6

_______Application Discussion
Excess power dissipation at high input voltage is the
limiting factor with linear regulators in 5-cell to 5V
applications. In battery-powered circuits, excess power
dissipation limits their utility if the batteries are fast
charged in place. At 1C charge rates, battery voltage
can rise as high as 1.8V/cell, and possibly higher if the
battery charger is connected when the batteries are
removed. If load current is flowing, the high input-output
difference may cause excess temperature rise. The
resulting hot spots can be a problem in small, hand-held
devices, many of which have temperature-sensitive
LCOs. However, linear regulators remain nearly
unbeatable in the 5-cell to 5V role if the continuous load
current is relatively low (perhaps 500mA continuous or
less) or if the batteries are charged outside the circuit.
The MAX714-MAX716 system solution ICs generate
multiple output voltages from a 5-cell stack. The MAX714
circuit shown here generates two 5V outputs (one at 2A,
the other at 100mA) and a negative LCD bias voltage
(-10V to -26V) controlled by an internal OAC. Other
family members have additional outputs in various
flavors. All contain supervisory functions such as lowbattery detection. The non-darlington Zetex ZTX788B
PNP pass transistors in this circuit have an amazingly
high minimum beta of 300 at 1A, holding the efficiency
decrease due to base current losses to less than 0.3%.

2
NEGAnVE
LCD OUT UT

-26V
AT25mA

13
U6

+
I47~F

vce

9 66
S2 7
.MAXIAI
15 6T MAX714

-=16 AG
910k

1 PG

Sl 5

-11 S6

I

+

100~F

-=-

01 = ZETEX ZTX750
02. 03: ZETEX ZTX7886
L1 = SUMIDA CDR74-101

LOW-BAnERY RESET ON/OFF
DETECT OUT OUT (OFF IS <1.5V.
ON IS >3.SV)

Figure 40. Triple-Output Subnotebook Supply with PNP Linear
Regulators

27

5 Cells to 5V via
Low-Dropout, Low-Power PWM Buck Regulator
______,Application Parameters
Input Voltage Range ................................... 5.2V to 11V
Quiescent Supply Current (VIN = 6V) ...................... 1.4mA
Max Load Current Capability (VIN = 6V) .................. 500mA
Efficiency (VIN = 6V. ILOAD = 100mA) ........................ 95%

100

-WI

90

urw

/

80
~

>to

70

Z

• Internal P-channel MOSFET
• Sma" a-pin package
• 170kHz fixed-frequency oscillator

W

C3

~

60
50
40

• Current-mode PWM
• 6J.1A shutdown mode

I

1/

30

lmA

lA

lOrnA
100mA
LOAD CURRENT

• 1.23V reference output

Figure 41. Efficiency vs. Load Current

_ _ _ _ _ _ _ _"elated Data Sheet
• MAX730A Buck Regulator
INPUT

_______,Application Discussion
If a buck regulator can achieve a very high duty factor, it
can mimic a low-dropout linear regulator and "ride down"
a falling battery voltage. This can work well in 5-cell to 5V
applications and similar low-dropout situations. The
MAX730A shown here can achieve duty factors in excess
of 95%, so dropout is only 200mV at a 100mA load.

ONIOFF
(OFF IS VIN - O.5V)

+

:
F

Il00llF

1 SHDN

l000pF

V+ 8

+5V
OUTPUT
:EFMAX730A LX.,.7_ _rY'rY'~,..-..-AIAXIM

O.llJF 4

5

CC

VOUT

-=-

-=-

330pF

1--+-----'
L1= SUMIDA CD75-220

Figure 42. Low-Dropout, Low-Power PWM Buck Regulator

28 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

.M-"IXI.M

6 Cells or 9V Transistor Radio Battery to
5V/3.3V at Low Power
______.Application Parameters
Input Voltage Range ..................................5.5V to 11.5V
Quiescent Supply Current (VIN = 9V) .........................1DIJA
Max Load Current Capability (VIN = 5.5V) .................1DDmA
(VIN = BV) ...................175mA

95

e:-

80

15

75

• 10llA shutdown mode
• Low-battery detect comparator

~

70

I

IJ~I~9J

85

1:;

• O.SV dropout voltage

IIIIII~

90

~
V+" 6V

V

to

VOUT" +5V
65

111111111

60

• Evaluation kit available

111111111

55
10~

100~

1mA
10mA 100mA 1000mA
LOAD CURRENT

_ _ _ _ _ _ _ _ Related Data Sheet
• MAX639 Buck Regulator

Figure 43. Efficiency vs. Load Current

_______Application Discussion
One specialized requirement in battery applications is to
squeeze every last drop from a 9V transistor-radio
battery, over the widest possible range of load current.
To meet this objective, the MAX639 has the lowest
quiescent supply current of any step-down regulator Ie
at the time of writing, with a guaranteed maximum
operating supply current of 20IlA. Also, for highest
efficiency, the MAX639 contains a monster P-channel
MOSFET switch. The normally high 94% efficiency can
be made as high as 97% by substituting a 470llH
inductor.
Although targeted at the common 9V transistor-radio
battery (PP3, ANSI 1604A type) the MAX639 is also a
good choice for 6-cell designs. The MAX639's ultra-low
supply current makes it great for memory-backup
applications, where 101lA of supply drain is on the same
level as the battery self-discharge current.
A fixed 3.3V-output version, the MAX640, is also
available.

~A)(I~

INPUT

6 V+
VOUTI-'1---,
.MAXI.M

MAX639

ON/OFF - - - t - - - '8i SHON

LX 5

+5V
OUTPUT

L1 "SUMIDA CD54-101

Figure 44. 9V Battery PFM Buck Regulator

_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ ___

29

5-12 Cells to 3.3Vat High Power
______Application Parameters
Input Voltage Range ....................................4.5V to 30V
Quiescent Supply Current (VIN = 15V) ...................... 630jJA
Max Load Current Capability (VIN = 4.5V) ••••.•••••.•.••••.•••• 3A

100

90

~

IIII

~IN~L

~

• N-Channel MOSFETs

",/ VIN =15V

zw

C3

• Small inductor

~

,/

;-

~

80

• Two preCision low-battery detection comparators

..l

!J.

VIN=30V

~

'I

-

• 25JlA shutdown mode
• 3.3V, 1.5% reference output

70
lmA

• 60kHz unity-gain crossover-excellent AC
response

lOrnA

100mA
lA
LOAD CURRENT

lOA

• Synchronization input
• 300kHzI200kHz fixed-frequency oscillator

Figure 45. Efficiency VS. Load Current

_ _ _ _ _ _ _ _Related Data Sheet
INPUT

• MAX786 Notebook SMPS
+

CI

_______Application Discussion
Cost, size, and efficiency are the driving factors in designing
a main power supply for a battery-powered system. This
circuit addresses each of these issues with a combination
of high operating frequency and all-NFET design.
This buck regulator operates as a fixed-frequency
current-mode PWM when load currents are high (1/4 load
to full load) and automatically switches over to a pulseskipping PFM mode at light loads. This idle-mode
characteristic results in high effiCiency over a wide range
of load current, yet still provides low-noise PWM
operation when inductor and switch currents reach high
levels.

33~F

-=-

35V

ON/Off

C2

13 ON5

330~F

- 11 SYNC

l~bF

10 REF

3 ON3

CS3 1-1'--_ _ _ _-'

2 SS3

FB31-'2:::.8_ _ _ _ _ _ _-'

-=-

O.D1~F ,L---...;G..,;ND.,.-....J
(OPTIONAL)
9

L1= SUMIDA CDR125-100
Q1,02 = SILICONIX Si9410DY
Cl,C2 =AVXTPS OR SPRAGUE 595D
01 = CENTRAL SEMICONDUCTOR CMPSH-3 OR lN5819
OTHER PINS ARE NO CONNECTS

Figure 46. 3.3V PWM Buck Controller with NFET Switch

30 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ AIIAXIAII

6·12 Cells to 5V at High Power
______.App'ication Parameters
Input Voltage Range .................................... 5.5V to 30V
Quiescent Supply Current (VIN = 15V) ......................270!JA
Max Load Current Capability (5V output, VIN = 6V) ......... .3A

100

VIN =6V

90
~
~
z

• N-Channel MOSFETs

80

w

<3

• Small inductor

~

• Two precision low-battery detection comparators

70
60

• Comparators double as high-side switch level
translators
• 251lA shutdown mode

lOA
LOAD CURRENT

• 3.3V, 1.5% reference output
• 60kHz unity-gain crossover-excellent AC
response

Figure 47. Effiency VS. Load Current

• Synchronization input
• 300kHz/200kHz fixed-frequency oscillator

_ _ _ _ _ _ _ _ Re'ated Data Sheet
• MAX786 Notebook SMPS

INPUT
C1

+

33~F

35V
---=~---,1""-12 SHDN
ON/IiFf

_______App'ication Discussion
There are three often-used methods for designing a
power supply for a portable system: from the ground up
with discrete components ("555s and baling wire"), from
a combination of general-purpose bUilding-block ICs, or
from system-level power-supply ICs (as seen later in this
collection). This circuit falls into the "building block"
category.
This buck regulator operates as a fixed-frequency
current-mode PWM when load currents are high (1/4 load
to full load) and automatically switches over to a pulseskipping PFM mode at light loads. This idle-mode
characteristic results in high efficiency over a wide range
of load current, yet still provides low-noise PWM
operation when inductor and switch currents reach high
levels.

C2
330~F

ON3

=
Mr~

11 SYNC

=

10 REF

CS51-'15"-------'

~

FB51-"2.:..1- - - - - - - - '

14 SS5

_ O.Ol~F
- (OPTIONAL)

GND

=
L1= SUMIDA CDR125-100
01.02 = SILICONIX Si9410DY
C1.C2=AVXTPS OR SPRAGUE 5950
OTHER PINS ARE NO CONNECTS

Figure 48. +5V PWM Buck Control/er with NFET Switch

MAXIM

31

6·8 Cells to 3.3V/5Vat Medium Power
_ _ _ _ _~Application Parameters
Input Voltage Range .................................... 6V to 16.5V
Quiescent Supply Current (VIN =6V) .......................1.5mA
Max Load Current Capability (VIN = 10V to 16V) ......... 800mA
(VIN =6V) ...................450mA
• Internal PFET switch transistor
• 170kHz fixed-frequency oscillator
• Current-mode PWM

100

IUIN =16J lJL

90
80

C
G

iE

13

~

~IN=116V

70

• 1.23V reference output

III

1,/ it

60

~

SO

VIN =

12V
1111

40

III

30

1111
Your: +sv

JI)

20

• 61lA shutdown mode

1]

~

'/

10

III

1111

lmA

lOrnA
100mA
LOAD CURRENT

• Evaluation kit available

lA

Figure 49. Efficiency VS. Load Current

_ _ _ _ _ _ _ _ Related Data Sheet
• MAX738A Buck Regulator
INPUT

______~Application Discussion
In many applications, size rules, and it makes sense to
use a device with an internal power transistor if possible.
The building block IC in this application employs an
internal PFET switch that fills the IC cavity to provide the
highest practical load capability in standard surfacemount packaging.
This workhorse PWM buck regulator provides high
efficiency conversion for 6- to 8-cell battery packs, 9V or
12V DC wall adapters, and similar low-voltage bulk
supply sources. The MAX738A's internal PFET switch
transistor has a much lower saturation voltage than the
NPN followers typically employed by bipolar IC switching
regulators. This leads to improved efficiency, particularly
at low input Voltages. See also the MAX744A (Iowdropout), MAX748A (fixed 3.3V output), and MAX758
(adjustable) versions.
The MAX1738 is a self-contained DIP version of the
MAX738A with all components, including the magnetics,
builtin.

ONIOFF
(OFF IS <02SV.
ON IS >VIN -O.SV)

I47J!F
1 SHDN

F

t5V

O.l~F

OUTPUT

2 VREF

I 3S~ND

01f1F

-=

4 CC

L1 = SUMIDA C07S-330

Figure 50. Medium-Power PWM Buck Regulator

32 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

.MAX•.M

6·8 Cells to +5V via
Negative Buck Topology
_ _ _ _ _~Application Parameters
Input Voltage Range ....................................-6V to -15V
Quiescent Supply Current (VIN = -5V) ......................1.5mA
Max Load Current Capability (VIN = -6V) ................. 500mA

100

90

.......

80

~

~ 70

+ Internal NFET switch transistor
+ Current-mode PWM

VIN = 12V

G 60
ffi

t3

rg

+170kHz fixed-frequency oscillator
+ 1.23V reference output

50
40
30

J

20
10

_ _ _ _ _ _ _ _ Related Data Sheet

lmA

+ MAX752 Boost Regulator

lOrnA
100mA
LOAD CURRENT

lA

Figure 51. Efficiency VS. Load Current

_______,Application Discussion
This circuit would normally be used to step down a
negative input voltage to a lesser, but still negative,
output voltage. In this particular case, a little judicious
rearrangement of the system ground reference allows
the negative output to become a positive one. However,
it only works in situations where the negative battery
terminal does not need to be tied to ground. For this
reason, the negative buck approach is most useful in
systems that don't require multiple output voltages
derived from the battery.
The advantage of this approach over a conventional
positive buck regulator is that the power switching
transistor is on the low side rather than the high side.
This arrangement makes it easier to drive the desirable
N-channel type of MOSFET. In this example, the
MAX752 provides the same performance as its
P-channel equivalent (MAX738) circuit with a smaller
(and less costly) power transistor.

.:l
~ SHDN
2

v+.L ~~lN5817 _.±_
7

~'..
'M~~
3 MAXIAII
6

150~FT

~.'

VOUT

I

-" SS MAX152 LX -'----'~~~
+47~F+ 4
5
L1
47~F;:"r'
CC
GND .::....
20~H_1:

"

10k

;:, 10k

-VIN

L1 = COILTRONICS CTX20-2
Q1 = 2N3906

Figure 52. 5V Step-Down via Negative Buck Topology

~~)(I~

_ _ _ _ _ _ _ _ _ _ _ _ _ _ _---------------------------------

33

5·8 Cells to 3.3V and 12V at High Power:
Buck Controller with Battery Charger
______Application Parameters
Input Voltage Range ..... .................................. 5V to 18V
Quiescent Supply Current (VIN :;; 5V) .......................... 1rnA
Max Load Current Capability (VIN:;; 5V) .... 1.5A (conligurable)

100

VIN=~I

90

II:

80

• 3.3V current-mode PWM buck controller
• 15V (12V) flyback controller
• Battery charger current source (buck SMPS)
• Dual PCMCIA Vpp outputs (OVNcc/12V)
• 300kHz fixed-frequency oscillator
• 10J.lA shutdown mode

~
>-

U
2:

15V

70

w

60

~

50

(3

40
30

3.3V
BUCK OUTPUT

~

Iii I I IIII Ii

Iii 1IIIIIIi

20
lmA

lOrnA

• 2.5V 1.5% reference output
• 5V low-dropout linear regulator output

VIN=

Figure 53. Efficiency

VS.

100mA
lA
LOAD CURRENT

lOA

Load Current

• Analog multiplexer
• Five level translators for high-side switching
• SPI-compatible serial interface
• Evaluation kit available

_ _ _ _ _ _ _ _ Related Data Sheet
• MAX781 Subnotebook SMPS

_______Application Discussion
One way to reduce a power supply's size and cost is to
integrate as many blocks as possible into a system IC
solution. Often, this approach results in a significant
cost savings compared to the building-block approach;
in this example, an integral flyback controller replaces a
separate battery-to-12V converter with a few turns of
wire, a few cents worth of silicon, and a 2.2J.lF capacitor.
Similarly. PCMCIA 12V switching functions are handled
by small, low-cost linear regulator transistors instead of
low rOS(ON) switching transistors.
The circuit shown here is a system-engineered solution
for small portable systems that have relatively light or
nonexistent 5V load requirements. To this end, the
MAX781 contains most of the analog-related circuit

blocks one might need in a power supply for a small
3.3V-only computer (an on-board 5V low-dropout linear
regulator also supplies 25mA for external loads). The
heart of this IC is a 3.3V buck controller with
synchronous rectifier and integral 15V flyback winding
controller. Other major functions include a switch-mode
battery charger. dual OV/3.3V/5V/12V PCMCIA Vpp
outputs, gate drivers for power switching via external Nchannel MOSFETs. and an analog multiplexer that allows
an external ADC to monitor various voltages within the
MAX781, such as the battery voltage and the output
voltages (for power-ready indication).
The battery charger is a switching-regulator current
source that assumes the charger intelligence resides offchip in a microcontroller. This SMPS block is a voltagemode PWM buck regulator optimized for a current
source rather than voltage-source output. The charger is
controlled through an SPI 3-wire serial interface, which
programs an on-board 7-bit digital-to-analog converter
(DAC) to set the charge rate. The core 3.3V/12V supply
is a high-performance buck regulator similar to those
found in the MAX782 chip that follows.
Note: At the time of printing, this circuit was not yet
characterized for 4-cell operation.

34 _ _ _ _ _ _ _-,-_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

MAXIM

5·8 Cells to 3.3Vand 12Vat High Power:
Buck Controller with Battery Charger

BATTERY
CHARGER
DC INPUT

ANAlOG MUX I/O
~

. - - - - - - - _ - 1 % VREF OUTPUT
2 4
31
29 AOUT AUXIN TEMP VREF
VCHG
VL 1-:;1""'8_--I-~>--+-

+

+5V OUTPUT

:::r:: 4.7~F
03

DCHG

AVPP 1-=-1--.--1---- }
PCMCIA
VppOUTPUTS
BVPP 1-=-1--.,..---1----

AltAXlAI'I
MAX781 VDD 1-,,6-+----+--------, +15V
r-~--t---~O""'UTPUT
28 V+
+3.3V
OUTPUT

...-_ _ _-'1"'-17 CSBAT
10~H

BST3

0.10

Tl

0.050

DL3

+

:::c 220IJ.F

SS3

4100

CS3
0.331lf

l

--....!..ILJCE

IN~~:~~E
I/O

~~~K

DOUT
----L:!..JINT
OSCILLATOR _ _-"-I
SYNCHRONIZATION
SYNC

30UT
25
GDl
36
GD2
___ }
GD3
GD4
3
GD5
4

~

GATE-DRIVER OUTPUTS
(FOR POWER SWITCHING)

01. Q2 = Si9956DY
03 = Si9405DY
T1 = SAE POWER INC #16026
4:1 TURNS RATIO

Figure 54. Subnotebook Computer Power Controller

~A~I~

_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __

35

6-12 Cells to 3.311, 511, and 12Vat High Power
______Application Parameters
Input Voltage Range .................................... 5.5V to 3DV
Quiescent Supply Current (VIN = 15V) ...................... 42DIJA
Max Load Current Capability
(5V output, VIN = 6V) ............... 3A
(3.3V output, VIN = 6V) ............ 3A
• Integral15V flyback winding controller
• Dual PCMCIA VPP linear regulators (OV, 5V, 12V at
60mAeach)
• Three precision low-battery detect comparators
• Comparators double as high-side switch level
translators
• 70llA shutdown mode

100

lili I

VIN =
90

~

C 80
b
1E
(3

~

VIN = 15\1

I 1111111 Vii

70

60

ililij,

JJW~~UT
i: ~ri~~;TI (1r~i11 nm
+3.3V SUPPLY IS OFF-

J
50
1mA

Q

10mA

100mA

1A

10A

LOAD CURRENT
Figure 55. Efficiency VS. Load Current

• 3.3V, 1.5% reference output
• 60kHz unity-gain crossover response

excellent AC

• Synchronization input
• 300kHz/200kHz fixed-frequency oscillator
• Evaluation kit available

_ _ _ _ _ _ _ _ Related Data Sheet
• MAX782 Notebook SMPS

_______Application Discussion
This dual PWM circuit is an integrated solution for the
main power supply of a mixed 3V/5V notebook computer.
Primary features are high efficiency over a wide range of
loading, small external components, and a high level of
integration.
There are seven rather than three output voltages,
depending on how you count them. The entire list follows:
• 3.3V main (buck SMPS)
• 5V main (buck SMPS)
• 15V high-side (forward/flyback)
• OV, 5V, 12V PCMCIA(VPPA linear regulator)
• OV, 5V, 12V PCMCIA (VPPB linear regulator)
• 3.3V reference (linear regulator)
• 5V standby (LOO linear regulator)
The 15V high-side voltage is generated via a flyback
winding on the 5V buck inductor. The 15V output is
regulated via an extra feedback input to the main 5V
buck PWM, which holds the synchronous rectifier on for
a longer time period than usual if the 15V output is low.
This action forces the flyback winding to operate in the
forward mode. Unlike other synchronous rectifier/
coupled inductor schemes, this rnethod ensures
excellent cross-regulation even with no load on the main
+5V output and with no penalty in quiescent supply
current.

Monster on-board gate drivers ensure fast switching and
low transition losses even at the MAX782's relatively
high 300kHz switching frequency. A novel current-mode
SMPS architecture, which employs a direct error voltage
and current-sense summing technique, results in small
filter capacitor values and corrects for load and line
transients within three or four switching cycles. Power to
the IC is automatically bootstrapped from the main 5V
SMPS output for reduced IC power consumption at high
input voltages.
See also the MAX786 (dual output) and MAX783 data
sheets for other notebook power-supply ICs.

_____ 4-Cell and 5-Cell Operation
This circuit can be easily adapted to lower battery
voltages by simply disconnecting the battery negative
lead from ground and connecting it to the +3.3V output.
A new topology is formed, with the +3.3V output
generated by an inverting topology and the +5V output
generated by bucking the resulting differential between
ground and the battery (3.3V + VSATIERY). These are
the major effects of connecting -VSATIERY to the +3.3V
output:
• The battery voltage can fall below 5V without loss of
regulation (minimum start-up = 4.2V).
• Battery ground is no longer the same as system
ground.
• A portion of the +5V load power, equal to

3.

3V 3.~V
+ BATTERY

X POUT

(5V)

must pass through the 3.3V inverter, reducing the 3.3V
external load capability.
• +3.3V must be turned on for +5V to work.
36 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ AIIAXIAII

6·12 Cells to 3.31(, 51(, and 12Vat High Power

BATTERY INPUT
5.5VT03OV
(NOTE 1)

~ 33~F
~

129
16
15

W, {

CONTROL
INPUTS

~~

~~
150~F 150~F

L1

10~

I

I lN58194~
D
=

~0~2)

O.Q1~F

MAX182

+3.3V ON/OFF
+5VON/OFF
OSC SYNC

BST3
OH3

OH5

LX5

~~

1 SS3
ON3
19
ON5
14
SYNC

22

~4.7~F

+5Vat5mA

~l~F

OV,5V,12V

~l~F

OV,5V,12V

'

DL5

It: N2

~O~10~H
lN5819

~h

VH

01-03
Ql-Q3

5

1:2.2

-'

=

+5V at3A
yomn

N4 _

21

Xl-

FB5 27
SS5

+15VAT 300nA

l~

25

CS5

~

,m,.I~ ,~i22~

23

--tf ~
GNO

NOTE 1: BATTERYVOLTAGERANGE6.5Vto3OV
WITH COMPONENTS SHOWN
NOTE 2: KEEP KELVIN-CONNECTED CURRENT-SENSE
TRACES SHORT AND CLOSE TO EACH OTHER.

24

BST5

LX3
30 DL3
35
CS3
34 FB3

=

10

VOD

32

N3

11

VPPB

AIAXIA4

~, ~f--;
Nl
. ji'

9

VPPA

DBO
17 OBl

25mn

VL

DAl

18

lN4148

+3.3Vat 3A

V+
DAO

::!:!:33~

28

_
-

O.Ol~F

(NOTE 2)

i

3

COMPARATOR SUPPLY INPUT

2,3,4

3

8,7,6

3

COMPARATOR INPUTS
COMPARATOR OUTPUTS

,

REF PGNO

3.3VAT5mA

~l~F

L1 =SUMIDA CDR 125-100
L2 =COILTRONICS CTX03-12067
Nl-N4 = S,9410DY

Figure 56. Triple-Output PWM Buck Controller

.MAXI.M

37

48V Subscriber-Line Telecom Power Supply
_ _ _ _ _~Application Parameters
Input Voltage Range ..................................... 35V to 72V
Quiescent Supply Current.. .... .......................... 20mA Min
Max Load Current Capability (VIN = 48V) ...................50mA
• "Steals" power from telephone lines
• Replaces holding coil
• Pulse-skipping PFM

70

\



u

30

c

• Does not affect voice signal

9""'

VBATT: -48V

\

~

5

I-

\

20

\

~

~

10

_ _ _ _ _ _ _ _,Re/ated Data Sheet

1k
2k
3k
LINE IMPEDANCE (0)

Ok

4k

• MAX638 Buck Regulator
Figure 57. Output Current Capability vs. Line Resistance

______--'Application Discussion
Although not battery-powered in the usual sense (the
batteries are large 48V lead-acid batteries at the central
office), this light-fingered circuit is quite useful in portable
systems that are connected to subscriber (household)
telephone lines, such as modems or telephone test sets.
If system power needs can be kept below 250mW, this
circuit eliminates the need for a battery pack or external
AC adapter altogether by "stealing" power from any
ordinary telephone jack without disrupting the voice
signal. In peripheral equipment such as a PCMCIA
modem card, any power taken from the telephone line
spares the battery in the host computer.
The maximum output current available from a subscriber
line in the off-hook state is determined by the source
impedance of the central office battery and series
resistance of the wire, rather than by any regulation or
code (such as Part 68 of the FCC Rules). The only
restriction on line impedance is that off-hook current be
at least 20mA (energizing a central office relay to
indicate a desire for network access). It is even
acceptable to short out the line, which is exactly what a
hold button does.
Maximum power transfer occurs when the source
impedance matches the impedance placed on the line.
The source impedance of a subscriber line varies
greatly, depending on the distance from the central
office. The need to draw at least 20mA to indicate an offhook condition makes perfect impedance matching
impractical. Instead, the circuit clamps the line with a
12V zener, which works well for line impedances up to
1700Q. Because the circuit sinks typically 35mA for all
load conditions on the +5V output, a ·wet" transformer
(one that sinks loop current) is not needed and a "dry"
transformer with a smaller, lighter core can be used
instead.

TElEPHONE
SUBSCRIBER LINE

SOLIO STATE RELAY
(SWITCH-HOOK)

RING

TO
HYBRID

r--'--~----'------

1N5817

-=iSV
LL1-:-SU-M-IO-A-CO-54-_3-31----+------"'OUTPUT

1001lf
6.3V

::r::
-=-

Figure 58. 48V to +5V Subscriber-Line Telecom Power Stealer

38 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

A4AXIA4

Section 5
3V-to-5V and 5V-to-3V Main Power Supplies
Designing 3V-to-5V and 5V-to-3V converters isn't much different from designing their batterypowered counterparts. Circuits that operate from a fixed input instead of a low-impedance battery
benefit from a narrower input voltage range, which eases concerns about worst-case duty factor
limitations, gate-drive levels, and peak currents. Fixed input circuits also allow for input capacitors
with lower operating-voltage and surge current ratings. Soft-start capability, a feature included in
the PWM circuits that follow, prevents high in-rush currents upon start-up, so the regulator doesn't
glitch the input supply and cause memory failure or activate power-fail alarms when the regulator
is powered from a system supply bus.

3V-to-5V and 5V-to-3V Converters
MAX741

3.3V to 5V at High Power

MAX731

3.3V to 5V at Low Power

MAX718

3.3V to 5V and 12V (Dual-Output PFM)

MAX786

5V to 3.3V at High Power

MAX763A

5V to 3V at Low Power

.MAXI.M

39

3.3V to 5V at High Power
______Application Parameters
Input Voltage Range .......... , .......................... 2.7V to 5V
Quiescent Supply Current (VIN = 3.3\1) ...................... 3mA
Max Load Current Capability (VIN = 3V) ....................... 1A
• Small SSOP package
• 150kHz fixed-frequency oscillator
• Current-mode PWM
• Synchronization input

95
VIN= 4V

85

~

• Evaluation kit available

JIN~

(; 65
z
w

c:;

~

55
45
35

• 260llA shutdown mode
• 1.23V reference output

V

75

/
II

25
lmA

lamA
100mA
LOAD CURRENT

lA

Figure 59. Efficiency VS. Load Current

_ _ _ _ _ _ _ _ Related Data Sheet
• MAX741 Universal Controller

_ _ _ _ _ _~Application Discussion
As 3.3V and mixed 3.3V/5V systems become more
popular, there is often a need to step up 3.3V to 5V. This
situation occurs frequently in peripheral equipment that
lacks access to the host system's battery. Desirable
characteristics in this situation include fixed-frequency
PWM operation (so that input current noise caused by
reflected ripple currents doesn't induce noise on the 3.3V
input supply), and soft-start.
Although optimized for a fixed 3.3V rather than battery
input, this pulse-width modulation (PWM) boost regulator
is a good starting pOint for many low-voltage designs that
require low noise and high efficiency. The PWM controller
Ie employed here is extremely versatile, and has been
referred to as the "Swiss army knife" of PWM controllers
due to its pin-programmed, reconfigurable nature.
For an alternative pulse-skipping PFM 3.3V-to-5V
converter, see the 5V to 12V at 500mA: MAX721 Boost
Controller circuit. When configured with a 5V output for
this role, it delivers ?50mA at 80% efficiency with no
component changes and can get by with smaller
capacitors than the MAX? 41 circuit.

INPUT
VIN = 2.7V TO 5V

150~~

r -_ _ _ _ _--<~_+-.....,6.3V -

L1 = COILTRONICS CTX20-4
Ql = MOTOROLA MT03055EL
01 = lN5817

Figure 60. 3.3V to 5V Boost Controller with External MOSFET

40 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

MAXIM

3.3V to 5V at Low Power
______Application Parameters
Inpul Voltage Range ...................................... 1.4V to 5V
Start-Up Supply Voltage (lLOAD = D) ..........................1.BV
Quiescent Supply Current {VIN = 3V) ..... .................... 2mA
Max Load Current Capability (VIN = 3V) .................. 350mA

90
80

C
(;

• 170kHz fixed-frequency oscillator
• Current-mode PWM

VvI~~~.W

70

Z

LU

U

~

• 35J..LA shutdown mode

50

40

• Evaluation kit available

I

60

• 1.23V reference output

_ _ _ _ _ _ _ _Re'ated Data Sheet

VIN =3vl
lh+1T

/
'/
II
1mA

Figure 61.

10mA
100mA
LOAD CURRENT

1A

Efficiency VS. Load Current

• MAX731 Boost Regulator

_______.App'ication Discussion
3V-to-5V converters can be useful in battery-powered
host systems as well as in peripheral equipment. One
example is a subnotebook computer that has omitted any
rotating disc drives, thus reducing the maximum load on
+5V to 2W or less. It may be simpler and less costly to
add a 3V-to-5V converter to a 3.3V buck than to have two
separate wide-input-range DC-DCs powered from the
battery.
Like the previous circuit, this PWM boost regulator is
ideal for low-noise, battery-powered applications such as
cellular phones, and is also well cast in the 3.3V-to-5V
role.
See also the MAX751, which is similar to the MAX731,
but has a smaller 8-pin SO package instead of a 16-pin
wide SO and a smaller switch transistor. Refer to the 2-3
Cells to 5V at Low Power via PWM Boost Regulator for
the circuit schematic.
Another alternative with fewer external components is the
MAX756 PFM boost regulator (page 10).

AIIAXIAII

INPUT
ON/OFF
(OFF IS < O.25V.
ON IS > VIN - O.5V)

V+FB----...

1 SHDN
A4AXIAII

2

MAX731

VREF

3 SS
4 CC

7

VOUT

~F6__+-~~-.~~
GNO 5

NOTES: PIN NUMBERS ARE FOR 8-PIN PACKAGES ONLY.
L1 =SUMIDA CD75-220

Figure 62. 3.3V to 5V PWM Boost Regulator with Internal MOSFET

41

3.3V to 5V and 12V:
Dual.Output Boost Controller
______ App'ication Parameters
Input Voltage Range ......... ......................... O.9V to VOUT
Start-Up Supply Voltage (I LOAD =0) ..........................1.4V
Quiescent Supply Current (VIN = 3V)
Main SMPS = 5V .............. 140jJA
Both SMPS ..................... 500jJA
Max Load Current Capability (VIN = 3V)
Main SMPS = 5V ............. 400mA
Auxiliary SMPS = 12V ........ 120mA

90

80

c~

70

~~

60

v.YrH*m-~~~-+~~

50

HVJ'+-t-Httttt-t-H++ttH-+++tHftlI

• Dual regulated outputs

VII.

40
lmA
lOrnA
LOAD CURRENT

1001lA

• Pulse-skipping PFM

100mA

• O.5MHz switching frequency
• Shutdown Mode
• 1.5% reference output (alive in shutdown)

Figure 63. Efficiency

VS.

Load Current

• Power-fail detection
• Evaluation kit available

_ _ _ _ _ _ _ _Re'ated Data Sheet

INPUT

• MAX718 Palmtop SMPS

_______,App'ication Discussion
Applications requiring a 3V-to-5V converter for supplying
Vee to peripheral equipment (through a PCMCIA card
socket, for example) often need a + 12V supply for flash
memory Vpp as well. This circuit easily delivers 5V at
400mA and 12V at 120mA when powered from a fixed
3.3V ± 10% supply, enough to support two PCMCIA
sockets. The 12V output can be programmed to 5V
under logic control, achieving the required Vpp = Vee
state without extemal switches or pull-ups.

AlAXIAI
MAX718
L -_ _ _ _ 8

"t FB3
1 SKUP

ON/OFF

-=

FS12r-:1=.O_ _ _ _-'

PFO 1-"9_ _•

3 3/5

CONTROL

II0s
5 VREF
O,221!F

:::r::

Q1 = MOTOROLA MID3055EL
OR 112 Si9942
L1, l2 = SUMIDA CD54-220

Figure 64, 3,3V to 5Vand 12V Step-Up Converter

42 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ AIIAXIAII

5V to 3.3Vat High Power
_____~Applicatlon Parameters
Input Voltage Range ..................................... 4.5V to 6V
Quiescent Supply Currant (VIN = 5V) ....................... 780JJA
Max Load Current Capability (VIN = 4.5V) ......................3A
~

90 1-+~1HlI-+++

~

• N-Channel MOSFETs

~

• Small inductor
• Two precision low-battery detection comparators

80 I-+~#III'-I+I++

• 1251lA shutdown mode
• 3.3V, 1.5% reference output

70 L...,L.LJ.JIJlL.l..U.
lmA
10mA
100mA
lA
LOAD CURRENT

• 60kHz unity-gain crossover-excellent AC
response

lOA

• Synchronization input
• 300kHzI200kHz oscillator

Figure 65. Efficiency vs. Load Current

INPUT

_ _ _ _ _ _ _ _Related Data Sheet
• MAX786 Notebook SMPS

_______,Application Discussion
There are many situations that might require a 5V to 3.3V
converter. Putting a 5V-to-3.3V converter on a daughter
card to upgrade an existing desktop system with a new
3.3V microprocessor is one such situation. Key
parameters in this case are size and cost; efficiency is
also important from a standpoint of heat and temperature
rise, but isn't critical for battery life (at least in the desktop
application). So, cost can optionally be reduced by
omitting the usual synchronous rectifier (the synchronous
rectifier doesn't help much anyway, since the rectifier
duty factor is low). In this circuit, the synchronous
rectifier is required for the boost gate-drive generator,
but can be a small low-cost 2N7002 instead of the usual
power MOSFET.
Buck regulators and linear regulators are both useful for
the 5V-to-3.3V task. The linear regulator (one can be
adapted from the 5-Cel/ to 5V with PFET Linear Regulator
circuit) exhibits decent efficiency in this role (66%,
discounting quiescent and drive losses). However, in
situations where the 5V input is derived from a battery,
66% is probably not acceptable and a switching
regulator solution is indicated, such as the one shown
here.
This buck regulator operates as a fixed-frequency
current-mode PWM when load currents are high (1/4 load
to full load) and automatically switches over to a pulseskipping PFM mode at light loads. This idle-mode

~A)(I~

ON!OFF

0.0250

~fpUT
+

:::r: C2
330~F

lOV

CS31-1' - - - - - - - '
FB31.!:2,,-8_ _ _ _ _ _---1
GND

L1 = SUMIDA CDRl25·100
01,02 =SILICONIX Si9410DY
01 = CENTRAL SEMICONDUCTOR CMPSH-3 OR lN5817
Cl ,C2 =AVX TPS OR SPRAGUE 5950
OTHER PINS ARE NO CONNECTS

Figure 66. 5V to 3.3V at High Power

characteristic results in high effiCiency over a wide range
of load current, yet still provides low-noise PWM
operation when inductor and switch currents reach high
levels.
For a pulse-skipping PFM alternative, see the MAX651
data sheet (a future product).

_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ ___

43

5V to 3.3Vat Low Power
______Application Parameters
Input Voltage Range ................................... 3.5V to 11V
Quiescent Supply Current (VIN = 5V) ...................... 1.4mA
Max Load Current Capability (VIN = 4.5V) ................ 500mA
Efficiency (VIN = 5V, ILOAD = 100mA) ........................ 92%

100

-WI

90

urw

I

80

C

>70
(.)

• Internal P-channel MOSFET
• Small a-pin package

as

13

~

60
50

• 170kHz fixed-frequency oscillator
• Current-mode PWM
• 61lA shutdown mode

40

I
1/

30
1mA

10mA
100mA
LOAD CURRENT

• 1.23V reference output

1A

Figure 67. Efficiency VS. Load Current

_ _ _ _ _ _ _ _ Related Data Sheet
• MAX763A Buck Regulator
INPUT

_______Application Discussion
5V to 3V conversion at low power levels is often required
for peripherals and daughter cards. Desirable characteristics for such DC-DC converters include fixedfrequency operation (so reflected ripple doesn't induce
low-frequency noise on audio or radio circuits in the host)
and soft-start.
This efficient little circuit sources a lot of power from a
tiny 8-S01C package and miniature external components.
Also, the MAX?63A can operate at low input-output
differential voltages (200mV) making it useful in 4-cellpowered and other low-dropout applications. The
MAX?63A has 400mA load current capability at an input
voltage of 4V (end-of-life of 4 NiCds).
See also the MAX?48A data sheet for a similar device
that has a larger switch transistor and 16-pin SOIC
package.

~

ON/OFF
(OFF IS VIN - O.5V)

F

1 SHDN

1000IpF2

=:

VREF

-=-

V+ 8

+5V

1"-7--...--''Y'\'Y'\'-----1~...OU-TP-UT
LX.-

3 SS

O.1fJF 4

CC

VOUT 5

-=-

-=-

330pF

'------11---<10-------'
L1 = SUMIDA CD75-220

Figure 68. 5V to 3.3V Buck Regulator with Internal MOSFET

__________________________________________________________________

Jt4~)(IJt4

Section 6
Display CircuifsLCD Contrast and CCFT Supplies
Liquid crystal displays (LCDs) generally need two types of power supplies: driver bias supplies
and backlight supplies. The LCD segment drivers typically need a negative or positive voltage of
approximately 10V to 24V. Display contrast is adjusted by varying the bias voltage. Bias voltage
generators come in many varieties, depending on the display size, the level of multiplexing, and
whether the display is color or monochrome. While many LCDs are set up for a negative bias
voltage, positive voltages are also becoming common, particularly for color panels.
The most efficient form of backlighting today is the cold-cathode fluorescent tube (CCFT) lamp,
which needs high-voltage AC power. A power supply to generate this AC voltage is typically not
part of the main power supply, as it needs to be located physically close to the display in order to
avoid power losses due to cable capacitance. There is both a system solution (MAX753/MAX754)
and a stand-alone solution for generating CCFT power in this section. Both are high-efficiency
supplies that can be connected directly to the main battery.

~L44

____________

~

__________________________________________

45

LCD Contrast with Digitally Adjusted
Negative Output
______.App'ication Parameters
Input Voltage Range ....................................... 2V to 6V
Quiescent Supply Current (VIN = 5V) ....................... 310~
Max Load Current Capability (VIN = 4.5V) ................. 25mA
(configurable)

90

v..

80

• On-board 5-bit DAC

C 70
~
15

• S-pin SO package

f5

13

• Drives PNPs or PFETs

.........

"

VIN ;5V

60
50

/

• Pulse-skipping PFM
40

• 71lA shutdown mode

100llA

• Evaluation kit available

_ _ _ _ _ _ _ _Re'ated Data Sheet

1mA
10mA
LOAD CURRENT (mA)

100mA

Figure 69. Efficiency VS. Load Current

• MAX749 Negative-Output Controller
INPUT

_______App'ication Discussion
LCD bias voltages can be generated with a flyback
winding on the main system Vee converter; however, that
approach wastes power because of high losses in the
linear regulators needed for post-regulating the rectified
winding voltage. A separate, stand-alone DC-DC
converter with an inherently adjustable output is usually
preferred.
This unique, tiny circuit contains an on-board 5-bit DAC
that adjusts the LCD contrast voltage from 1/3 full scale to
full scale via a serial interface, eliminating unreliable
potentiometers. An external switch transistor allows for
trade-ofts in power level, cost, breakdown voltage, and
efficiency; choices range from a cheap 2N290? A to a
fast, low VeE (sat) ZTX?50. Highest efficiency (up to 85%)
is obtained by shorting out the 4?OQ resistor and adding
a PFET such as the Siliconix Si9400DY. While the circuit
shown is tailored for a fixed 5V supply, it is easily adapted
to direct battery connection in 2- and 3-cell systems (see
MAX? 49 data sheet). Also, the 25mA capability of this
circuit is given only as an example; being a controller, the
load capability can be increased by sizing the external
components appropriately.
The output voltage can be adjusted via the serial
interface, or by an external potentiometer or PWM signal.

V+

ro·~l
INPUTS

MAXIM

2 ADJ MAX749 DHI 7
-24V
OUTPUT

3 SHDN
4 FB

11 ; SUMIDA CD54-470
Q1 ; ZETEX ZTX750

1.2M

Figure 70. LCD Contrast Supply with DAC and External PNP Switch

46 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

..MAXI..M

LCD Contrast, 5V to Negative Output
via Autotransformer
______Application Parameters
Input Voltage Range ........................................4V to 6V
Maximum VIN - VOUT Differential ..............................30V
Quiescent Supply Current (VIN = 5V) .......................3.7mA
Max Load Current Capability (VIN = 4.75V) ................ 50mA

90

.

80

~ 70
~

• 185kHz fixed-frequency oscillator

w

C3

60
it
w
SO

• Current-mode PWM
• 111A shutdown mode

,
VIN= S.SV

.

!VIN= 4.SV •

.

'/

2:

• Internal P-channel MOSFET

.........

/

40

• 1.23V reference output

lmA

lOrnA
LOAD CURRENT

• Evaluation kit available

100mA

Figure 71. Efficiency vs. Load Current

_ _ _ _ _ _ _ _ Related Data Sheet
• MAX759 Inverting Regulator

_______Application Discussion
Monolithic construction is the advantage of this circuit, as
it features a large, low-saturation, internal P-channel
MOSFET. The topology shown here trades off higher
peak switch currents for a reduced stress voltage on the
switch transistor via an autotransformer. The
autotransformer shown is an off-the-shelf 0.2" diameter
SMT toroid device that reduces the voltage seen at LX
according to the turns ratio. Efficiency is over 80%, which
is quite good for an inverter having a large input/output
voltage ratio and operating from a 4.5V input.
The autotransformer must have less than 2% leakage
inductance; otherwise, overvoltage transient spikes
generated by the uncoupled magnetic field may damage
the switch transistor. Mount the autotransformer close to
the device to minimize PC trace inductance in the LX
lead.

1.r-_ _ _-.

INPUT

13.14 V+
LX 11.12

-=ON/OFF
(OFF IS <0.25V.
ON IS >VIN -ll.SV)

2 SHDN

DRV

AOIAXIAII

MAX159
10 GND
VREF

CC

r----<~

OUTPUT
OV TO -24V
ATSOmA

147~F

0.047~F

I

LCD
CONTRAST
ADJUST

L1 = COILTRONICS CTX100-1 OR MAGNETICS. INC. "KOOL-MU" 77030-A7
30 TURNS AND 30 TURNS 26 AWG

Figure 72. 50mA LCD Contrast Supply with Internal MOSFET

.MAX•.M

47

LCD Contrast, 5V to Negative Output
at Micro Power
______App'ication Parameters
Input Voltage Range ........................................4V to 6V
Maximum VIN • VOUT Differential ..............................24V
Quiescent Supply Current (VIN = 5V) ....................... 500~
Output Adlustmeilt Range (as shown) ...............-5V to -15Y
Load Regulation (OmA < ILOAD < 10mA) ....................75mV
Max Load Current Capability
(YIN = 4.5V, VOUT = -15V) .... 10mA

70

60

g
~

l..-

III

iii

VINI=I~~

50

Vour =-15V

w

i3
~

i-

j
40
30

V

l/

• Internal P-channel MOSFET
20

• Pulse-skipping PFM

100pA

lmA
LOAD CURRENT

• Low-battery detect comparator

lOrnA

+1.31V reference output

+70llA shutdown mode

Figure 73. Efficiency vs. Load Current

_ _ _ _ _ _ _ _,Related Data Sheet

+ MAX634 Inverting Regulator
________App'ication Discussion
Systems such as cellular phones with small multiplexed
LCD displays can often get by with a flea-power
regulator to provide the LCD bias voltage. The pulseskipping regulatorlC used here (MAX634) is a sister to
the original micropower DC-DC IC, the MAX630.
Although mature, the MAX634 is often still a costeffective solution in low-power applications.

Note that the maximum input-to-output voltage
differeritial, normally 24V, can be extended by
substituting an autotransformer for the inductor (see
Rgure 75 below).

INPUT
INPUT
4.5V1o lOV

+

1OI'FI

I
VFB ""8.......,,,,,,\ --'\/JO\,~
18k--'....::..::c.....
LBO
VREF f-+_ _
.-..011lf
CX MAX634+VS 6
.:C

lN4148
-.1-..----=r

~.~_.--4

(OFF IS>3V.
ON IS  3V.
ON IS < O.2V)

1N4148
3 CX
_*---.-_---"1
47pF

LX F5------~__.t-..-

22~F

35V

I

O.lIlF

I

10k

15k
D1, D2" 1N5819 (89% EFFICIENCY) OR 1N4148 (80% EFFICIENCY)
L1 "COILTRONICS CTX100-4 (7. 8 CELLS INPUT)
SUMIDA CDR-74 OR COILTRONICS CTX100-2 (6 CELLS INPUT)

Figure 77. High-Efficiency Negative-Output Boost Regulator with Charge Pump
~A)(I~

____________________________________________________________

49

LCD Contrast, 5·8 Cells to Positive Output
______.Application Parameters
Input Voltage Range .................... ................ 4.5V to 15V
Quiescent Supply Current

100

(VIN = 5V, Your = 26V) ...................................... 550JJA
(VIN:: 9.6V, Vour= 38V) ......................................1mA

90

Max load Current Capability (VIN =4.5V, Your =38V) .. 30mA
load Regulation .......................................... O.06%/mA
line Regulation . ............................................O.16%N
Output Noise ...............................................200mVp·p

I

I

VOUT =26V, VIN =B.SV, L1 =1OO~H

C
>'-'

00UT

ifi

u 80

~

I

=38V, VIN =B.SV, L1 =

SO~H

VOUT =38V, VIN =SV, L1 =SO~H

70

60

• Low·side external N-channel MOSFET switch

lOrnA
20mA
LOAD CURRENT

• Pulse-skipping PFM

30m A

• low-battery detection comparator
Figure 78. Efficiency VS. Load Current

• 16J.tA shutdown mode

_ _ _ _ _ _ _ _ Related Data Sheet
• MAX641 Boost Regulator

_ _ _ _ _ _~Application Discussion
Many color LCDs, plus a few of the monochrome type,
need a positive instead of negative contrast adjustment
voltage. The MAX641 circuit shown here is good in this
role because it has high efficiency and a relatively wide

input voltage range. The 90% efficiency of this circuit is
5% to 10% better than that of similar circuits made with
bipolar transistors.
This circuit's input voltage range makes it suitable for a
+5V regulated input or a direct battery connection. For
input voltages above 7V, substitute a 100J.tH inductor for
L 1 in order to maintain low output noise and ripple
(Coiltronics CTX100-4).
See also the MAX761 data sheet (a future product).

Ll
INPUT
... _ _ _--.---'-AASO'-"~HJ0---.--1-1N4~93-S---___,t_26VT038V
...
OUTPUT

I
+

-

MAX641 VF81'-7_ _ _ _~_...

S60k

22~F

AT SOV
LOW-ESR

20k

OPTIONAL
SHUTDOWN
CIRCUIT

10k
~

-- -

ON/OFF

- - --- -- -- --- --- -----

(OFF IS < DAV,
ON IS> 1V)

-:::-

-:::-

L1 = COILTRONICS CTXSO-4 OR SUMIDA CD-lOS SERIES

-:::-

Figure 79. LCD Contrast Supply, 5-8 Cells to Positive Output

50 _ _ _ _~------_ _ _- - -_ _ _ _- - ' - _ -_ _- - - - - - .MAXI..NI

CCFT Backlight Inverter with
Current·Fed Royer Oscillator
______ Application Parameters
Input Voltage Range ....................................4.5V to 16V
Max Output Power Capability (VBATT =4.5V) ................. 6W

CCFT BACKLIGHT
C1
33pF
3kVT

•

01
1N4148

r-I

T1

~9

~

• Powered directly from battery
• Resonant (sine wave) operation

C3

1D~F ~

• Shutdown control input

02
1N4148

+
VIN 4,5V
TO 16V

_ _ _ _ _ _ _ _ Related Data Sheet
• MAX752 Boost Regulator

_______,Application Discussion
This MAX752 circuit is provided as a stand-alone
alternative to the MAX753 solution given on the following
page. Efficiency is about equal for the two circuits,
although the MAX752 lacks the MAX753's on-board
DACs and contrast voltage output.
The MAX752 boost regulatorlC acts as a switchingregulator current source to feed the tail of a traditional
Royer-type self-oscillating DC-DC converter, The
MAX752 operates in a current-limited pulse-skipping
mode, regulating the tube current by drawing rapid
bursts of current. The Royer circuit drives a 33: 1
transformer that steps up the battery voltage to AC high
voltages (as high as 1200V to strike the lamp), The
capacitor C2 and the primary inductance of the
transformer form a resonant tank circuit, which provides
a low-EMI sine wave drive signal to th,e tube, A halfwave-rectified signal proportional to tube current is
returned to the MAX7S2's feedback input. Brightness is
adjusted by potentiometer R2,

R6
D3
1k
1N5819
INPUT
4.5VTO 16V-.----~I----,
R2
5Dk
V+
7 YOU!

CDMP 6

4 _ _ _..
CCFC5
ID,l~F

T1 = SUMIDA 6345-020 OR COllTRONICS CTX11D092-1
II = COILTRONICS CTX1DD-4
C2 = WIMA FKP2 (LOW LOSS)

Figure 80, Stand-Alone CCFT Backlight High-Voltage Inverter

51

LCD Contrast and CCFT Power,
6-8 Cell System Solution
______,Application Parameters

_______Application Discussion

Battery Voltage Range .••••....•......•.................•. 6V to 20V
Quiescent Supply Current (VIN = 15V) ........................ 3mA
Max load Power Capability •.••..•....•.•...••• 3W (configurable)

The small cold-cathode fluorescent tube (CCFT) lamps
often used to illuminate the LCD of a portable computer
need a couple of watts of 400V AC power. This voltage
must reach 1200V or so upon start-up in order to arc and
turn on the lamp.
In a modern computer design, the backlight usually
represents the single greatest continual drain on the
battery, so extra circuitry added to improve the CCFT
power supply efficiency is well spent. This circuit has
been optimized with the specified components to
achieve 80% efficiency.
The DC contrast voltage output is generated with either a
positive boost topology (MAX754) or a hybrid of boost
plus charge pump for negative voltages (MAX753), The
contrast generators employ a pulse-skipping PFM
scheme with the regulation point set by one of the two
on-board 5-bit DACs, The CCFT voltage is generated by
a zero-current-switched quasi-resonant flyback topology,
requiring only one power switch transistor (unlike a
current-fed Royer circuit, which requires three), Tube
current is sensed and then applied to an error amplifier
that generates an error signal proportional to the DAC
setting and actual lamp current. This error signal is fed to
a V/F converter, which adjusts current (and brightness)
by changing the switching frequency,
Note: CCFT lamp characteristics vary greatly, so it is
essential to consult Maxim's Applications Department for
specific component recommendations for each new
design.

• Dual output: 400V AC CCFT and DC contrast
voltage
• Digitally adjustable-dual on-board DACs
• Resonant-mode CCFT operation
• 80% efficiency
• 751lA shutdown mode (retains digital code)
• External low-side N-channel MOSFETs
• DC contrast voltages can be positive or negative
• Evaluation kit available

52 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ .AIt.AXIAIt

LCD Contrast and CCFT Power,
6·8 Cell System Solution
BATTERY (8.SV TO 16V WITH COMPONENT VALUES SHOWN)
INPUT

.5V INPUT
LCD OUTPUT
-12VTO-24V
10.2kl%
LCD
CONTRAST 10k
(OPTIONAL)

1 VDD

!

LCDFB 16

_+-_....2 LCDADJ

DIGITAL
CONTROL
INPUTS

VBATI 15
AIAXIAt
14
3 LCDDN MAX753 VIND 1-------11

4 CCFTON

LCDOUT 13

_+_-"15 CCFTADJ
6 GND

-=

7 VREF

CCFTOUTfll!..-=--------I
ISCCFT,,1.:..0_ _ _ _ _ _~

O.22JlFI
lOOk

Dl-D4=1N4148
L1 = SUMIDA CD75-220
L2 = COILTRONICS CTX2Q-4
Tl = COILTRONICS CTXOl-12085-1
QJNQ1B = Si9953DY

Figure 81. Dual-Output LCD and CCFT Power Supply with Digital Adjustment

..MAXI..M

53

Section 7
·5V Generators
Making a negative 5V supply for a battery-powered system is often just a matter of adding a diodecapacitor charge pump to the switching node of a boost converter or adding a transformer winding
to the inductor of a buck converter. If tight regulation or efficiency requirements mandate a standalone -5V generator, consider the switching regulator and charge-pump solutions given here.

"ntPe

Source Voltage

MAX741
MAX735
MAX639
MAX660
MAX1044
MAX739

4-8 cell battery or +5V bus
+5Vbus
2-4 cell battery or +5V bus
+5Vbus
+5Vbus
5-8 cell battery

~AXI~

Description
PWM with external PFET
PWM with internal PFET
PFM with internal PFET
Charge pump
Charge pump
PWM with internal PFET

__________________________________________________________

55

-5V from +5V or 4·8 Cells at High Power
______ Application Parameters
Input Voltage Range .......................................4V to 15V
Quiescent Supply Current (VIN =5V) ..........................3mA
Max Load Current Capability
(VIN = 4.75V .......................................................1A
(VIN = 12V) ..................................................... 1.25A

90

.JJ:l
I I 111

I~

VIN=SV

I III

~

70

15

60

~

1:;
(3

tt

• 150kHz fixed-frequency oscillator

so

• Current-mode PWM

40

• Synchronization input

VIN= 12V
80

30

• 30~A shutdown mode

1I

V
lmA

lOrnA
100mA
LOAD CURRENT

lA

• 1.23V reference output
• Evaluation kit available

Figure 82. Efficiency VS. Load Current

_ _ _ _ _ _ _ _ Related Data Sheet
• MAX741 Universal Controller
INPUT

_______.Application Discussion
-5V at high power is occasionally needed in portable
equipment for analog or ECl circuitry. A standard
inverting topology is usually indicated, as shown in Figure
83. The relatively wide input voltage range of this circuit
makes it useful for 4-8 cell NiCd battery packs as well as
with fixed 5V input. The MAX? 41 "Swiss army knife" PWM
controller is pressed into service here as an inverter,
driving an external P-channel MOSFET high-side switch.
The shrink small-outline package (SSOP) can help keep
the surface-mount version of this circuit small.

(OFF IS < O.2SV.
ON IS HI-Z)

ON/OFF -1----1--1
9 1----'
V+
1 SLOPE

~......._--1---"-16 VREF

FREQ

S .......~-~
CSAl-'l::c.

4 PflfN

~-I----1-!---"-I8 SS ~ CSBI-'-14"---~
7 UVLO

OUTBI-'-17"",,_,\.a>

10 EAO
3 VSEL

OUTA 18

12 DUTY

EAIN 11

13 POL
L1 =COILTRONICS CTX20-4
TO Your (VIN < 8V)
TO GND (V IN > 8V)

Figure 83. -5V from 5V at 1A: Inverting PWM Controller

56 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

..NII.AXI..NII

-5V from +5Vor 5·8 Cells at Medium Power
_ _ _ _ _--iApp'ication Parameters
Input Voltage Range ....................................3.8V to 11V
Input Voltage Range (non-bootstrapped mode) .. 3.8V to 16.5V
Start-up Supply Voltage (ILOAD = 0) .......................4V Max
Quiescent Supply Current (VIN = 5V) .......................1.8mA
Max Load Current Capability (VIN = 5V) ............... .... 200mA

80

II

70

~ 60
~

+165kHz fixed-frequency oscillator
+ Current-mode PWM
+ 1.23V reference output
+ 1IJ.A shutdown mode

_ _ _ _ _ _ _ _ Re'ated Data Sheet
+ MAX739 Inverting Regulator

it
w

50
40
30

V

V

z

w

13

.... "'-:P'

VIN~~J

~

Iv
I VIN=6V

V
lmA

10mA
l00mA
LOAD CURRENT

Figure 84. Efficiency vs. Load Current

_______App'ication Discussion
When cross-regulation or efficiency needs dictate a
stand-alone regulator instead of a flyback or coupledinductor solution for a negative-output DC-DC, a simple
inverting (sometimes called buck-boost) topology
provides a low-cost solution that uses off-the-shelf
magnetics. This -SV generator is optimized for battery
voltages above SV, but not exceeding 16.SV. The
MAX739 is a current-mode PWM regulator similar to that
found in the -5V from 5V at Medium Power circuit that
follows, but it exchanges a larger package size and
higher cost for a wider supply voltage range.

,--_~-el.l--'.3.1-14 V+
2 SHDN
AIIAXIAI

5 SS MAX739VOUT 8

-sv

lN58l7

OUTPUT

+

1501lf

=
L1 = SUMIDA CD75-150

Figure 85. Inverting PWM Regulator

~~I~

___________________________________________________

57

-5V from +5V at Medium Power
_ _ _ _ _~Appl;cation Parameters
Input Voltage Range •••••.••••••••••••••••••••••.••••••••• 4V to 6.2V
Quiescent Supply Current (VIN = 5V) ••••••••••••••••••••••• 1.6mA
Max Load Current Capability (VIN = 5V) •••••.••••••••••••• 200mA
• Small S-pin SO package
• 160kHz fixed-frequency oscillator

90

~

70

13

60

~
z

m

/~

,,

111I~IN~4V

lE
w

• Current-mode PWM

50

• 10J.1A shutdown mode

40

JI
I

• 1.23V reference output

30
lmA

• Evaluation kit available

_ _ _ _ _ _ _ _Related Data Sheet

11I1~IN~6V

80

10mA
100mA
LOAD CURRENT

lA

Figure 88. Efficiency vs. Load Current

• MAX735 Inverting Regulator

______~Appl;cation Discussion
-5V at moderate power is often needed for audio circuitry
or special interfaces. The PWM solution shown here
provides a low-noise solution having tiny external
components. This circuit is internally bootstrapped, such
that the internal P-channel switch receives as gate drive
the full difference between input and output voltages
(10V). The resulting low rOS(ON) provides output current
capability that is unusually good for an 8-S01e inverter
with internal power transistor.

INPUT
(OFF IS <0.25V,
ON IS > VIN - O.SV)
ON!OFF

r-----,

I SHON

v.

8

.--....._--'1VREF
LXF-7---'-"UIJ0'-r1
Rl'
+ 10llF 3 ~
6
30k
SS
GNO
4 CC
R2'
300k

F--+--+-

-5V
OUTPUT

-=- ~
-

C2
IOO!1F
IOV

L1 = SUMIDA CD54-100
• COMPONENT MAY BE OMlffiD IF ILOAD IS LIMITED TO IOOmA

Figure 87. -5V from +5V at 200mA: PWM Inverter

58 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ AII.AXIAII

-5V from 5Vat Low Power via
Inverting Regulator
_ _ _ _ _ _Application Parameters
Input Voltage Range ......................................1.2V to 6V
Start-Up Supply Voltage (lLOAO = 0) ............................ 1V
Quiescent Supply Current (VIN =5V) ......................... 35J,JA
Max Load Current Capability (VIN = 4.75V) .............. .. BOmA

90
VIN : 6V

VIN: 3.SV

C
>u

• Pulse-skipping PFM
• Buck regulator

Ie used as inverter

• 10J.LA shutdown mode

JJll1

80

iij
t:5

70

rr-

'/

60

50
EE
w
40

II

30

20

_ _ _ _ _ _ _ _ Related Data Sheet

10~A

100~A

1mA
10mA
LOAD CURRENT

100mA

• MAX639 Buck Regulator
Figure 88. Efficiency

VS.

Load Current (three input voltages)

______---iApplication Discussion
"Every step-down IC is an inverter and every inverter IC
is a step-down." That statement is nearly always true:
Most any buck regulator chip can be fooled to produce
negative output voltages, and likewise, inverters can
work as buck regulators. This trick, which belongs in
every designer's toolbox, is done by rearranging the IC's
ground pin reference and substituting the correct switchmode topology. In this case, a micropower PFM buck
regulator IC (MAX639) is employed as an inverter. The
IC attempts to regulate the feedback pin (V OUT ) at a
point 5V more positive than the GND pin; since VOUT is
at circuit ground, GND is forced to -5V. The trade-off for
using the IC in this unintended manner is a shift in the
allowable supply range; in this case, the maximum
supply voltage capability is reduced because the circuit
configuration is inherently bootstrapped.
This particular variation on the buck-becomes-inverter
theme has earned a place in this collection by exhibiting
good efficiency at light loads (due to its pulse-skipping
control loop). Efficiency can be improved by 5% or so
over that shown in the graph above by increasing the
inductor value to 470J.LH. The output feedback resistor
divider and 1000pF capacitor are optional; if 100mV or
so increased noise is acceptable, remove the feedback
components, connect VFB to the -5V output, and ground
the VOUT pin. Always be sure that a 0.1 J.LF ceramic
bypass capacitor is soldered directly to V+, in addition
to the usual bulk bypass capacitor.

~A)(I~

INPUT
6 V+
8 SHDN

2

VOUT 1
VFBt'7------,

-5V
OUTPUT

LB~NDt-4'--=~>-t....-.....J

3 LBI

LXt'5~-tlIIr---.

L1: SUMIDA CD75-101

Figure 89. -5V from 5V at 80rnA: PFM Inverter

__________________________________

59

-5V from 5Vat Low Power via
Charge Pump
_ _ _ _ _~Application Parameters
Input Voltage Range ...................................1.5V to 5.5V
Quiescent Supply Current (VIN = 5V) ....................... 10DIlA
Output Impedance .•.......................•.....•....•.......... 6.50
Max Load Current Capability (VIN = 4.75V) ...............1DDmA

100

ttlt"'4.l

90

VIN=5V

80

e.:.

>......

70

ii'i 60

• No inductors

C3

~

• Small 8-pin SO package

40

• O.65V voltage drop at 100mA

30

• 10kHzl45kHz fixed-frequency oscillator
• Unregulated output

/

50

20
10

V
101lA

1001lA

• Also works as a doubler (+5VIN, +10VOUT)
• 10ILA shutdown mode

lmA
lOrnA
LOAD CURRENT

100mA

Figure 90. Efficiency vs. Load Current

_ _ _ _ _ _ _ _ Related Data Sheet
• MAX660 Charge Pump
INPUT(-t5V)

______~Application Discussion
The unregulated charge pump approach shown here is
less expensive than the equivalent switching regulator,
and has very high efficiency at light loads for a low-noise,
fixed-frequency converter. Since an unregulated charge
pump has no pulse-skipping control loop, there is no lowfrequency subharmonic content in the output ripple
waveform, making it useful in cellular phones and other
low-noise applications. If desired, OSC can be driven
directly by a system clock to set a precise switching
frequency. An "unregulated" charge pump actually
regulates fairly well if operated from a fixed input voltage.
In this situation, the MAX660 looks like a 6.S0 resistor.
An unregulated charge-pump IC such as the MAX660
directly inverts the input voltage, such that the negative
output voltage tracks the input (OdS PSRR). Load
regulation is determined by the rOS(ON) of the internal
MOSFET switches. A charge-pump circuit is a good
alternative to the previous inductor-based inverters in
applications that can tolerate OdS PSRR and imperfect
load regulation. In the common SV to -SV application,
OdS PSRR is often not a problem because the input is a
regulated SV supply bus.
The MAX66S is a very similar device with a slightly
higher maximum input voltage range. The MAX66S can
tolerate an BV input but has a larger SOIC package.

(OFF IS < O.3V,
ON IS >2.8V)

1 FC
CAP_ _

F---t>f--j-- ON/OFF
3 GNO

MAX660

4 CAP-

F-__._--j-- -5V OUTPUT
1OO1IF~

+
I1011F

'OPTIONAl, FOR SHUTDOWN

Figure 91. -5V from 5V: Charge Pump Solution

60 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

AIIAXIAII

-5V from 5V at Micro Power via
Charge Pump
_ _ _ _ _~App.ication Parameters
Input Voltage Range ....................................1.5V to 10V
Quiescent Supply Currant (VIN = 5V) ......................... 501lA
Output Impedance ................................................650
Max Load Current Capability (VIN = 4.75V) ................ 1OmA

100

C
1:;
C3

~

• 8kHz/65kHz fixed-frequency oscillator
• Unregulated output
• Can operate as a doubler (VOUT

=2 x VIN)

• 1.5J1A shutdown mode

_ _ _ _ _ _ _ _ Re.ated Data Sheet

~1I1

80

i'5

• No inductors

111111

90

J

70

VIN = 5V

60
50
40
30
20

!/

10
10~A

100~A

lmA
lOrnA
LOAD CURRENT

100mA

Figure 92. Efficiency vs. Load Current

• MAX1044 Charge Pump

______-'App.ication Discussion
This circuit is a scaled-down version of the -5V from 5V
at Low Power: MAX660 Charge Pump circuit, and the
comments given there apply equally here. The MAX1044
is basically identical to the MAX660, except for a
somewhat higher input voltage range, ten times reduced
output current capability, and lower cost. The final
variant of this family of unregulated charge-pump ICs
(which all have a standard pinout) is the ICL7662, which
again trades off output resistance/current capability for
increased supply voltage range. The ICL7662 can
tolerate a 20V input, but has a 1400 typical output
resistance (V IN = 5V).

1 BOOST

V+ 8

INPUT (+SV)
(OFF IS < O.3V.
ON IS> 2.8V)

2CAP+_ OSC
MAXI044
LV 6 lN4148"
3 GND

ON/OFF

4 CAP-

-fN OUTPUT

VOUT

"OPTIONAL. FOR SHUTDOWN

Figure 93. Micropower Charge-Pump Inverter

~~I~

____________________________________________________________

61

Section 8
Flash Memory, PCMCIA,
and Other + 12V Power Supplies
Vpp is a label for the 12V DC input terminal on flash memory ICs. Proper operation of the flash IC
restricts this voltage to a narrow window, sandwiched between the conditions of overvoltage (with
possible damage to the memory), and undervoltage (which can cause faulty programming due to
insufficient charge transfer). Consequently, the 5% data sheet tolerance limit is an essential
specification. The circuits that follow are designed to generate accurate, clean Vpp waveforms
that have fast rise times without overshoot and ringing.
Flash-memory power supplies are commonly specified in multiples of 30mA - the worst-case Ipp
current drawn by a typical byte-wide flash EEPROM chip during its erase cycle. This current is
nearly independent of the memory size, even for experimental VLSI devices. Therefore, most of
the following solutions are optimized for 30mA, 60mA, or 120mA output capability.

~AXI~

________________________________________________________

63

5V to 12V at 30mA via
Charge Pump
______.Application Parameters
Input Voltage Range ........... ,.................. '" ..4.5V to 5.5V
Quiescent Supply Current (YIN = 5V) .......................3001lA
Max Load Current Capability (VIN = 4.75V) ................30mA
Start-Up Rise Time ..........................................400J.lSec

80
V:N

~ ~~~~

70

VIN=5.2SV

~

>u
zw

60

~

50

J. t-I
.J.+I

/'
,

13

• No inductors
• Pulse-skipping PFM
• 1JlA shutdown mode
• Evaluation kit available

/
1/'

40

30
1DOpA

lmA
lOrnA
LOAD CURRENT

100mA

_ _ _ _ _ _ _ _Related Data Sheet
• MAX662 12V Charge Pump

Figure 94. Efficiency VS. Load Current

_______Application Discussion
12V at 30mA is a common requirement in portable
equipment, for both mass-storage and software-update
applications. +12V for mass storage or memory cards
usually needs 60mA or more, but many palmtop
applications can get by with 30mA by programming 8
bits instead of 16 bits at a time. Software and bios
update applications, typically implemented with bootblock flash chips, only require 30mA since 8-bit-wide
programming is nearly universal.
The MAX662 regulated charge-pump IC first doubles the
input voltage and then adds SV onto that, using the
traditional flying-capacitor voltage-doubling technique. A
pulse-skipping pulse-frequency modulation (PFM) control
loop forces the output down to 12V ±S% over all line and
load conditions by gating off the charge pump when the
output is in regulation.
The MAX662 circuit is extremely small, taking up only
O.2Sin2 of PC board territory. The internal oscillator
frequency is O.4MHz, keeping capacitors small.
Guaranteed 30mA output current capability makes it a
good fit for the embedded control and software update
types of flash memory applications.

INPUT

+12V
r-------OUTPUT

-

~-__+-'5"'1VCC
O.lJlF

6 Your

C2+ 4

~-,--_7'-1GNDMAX662 Cl+ 2
_---t_ _ _,8 SHDN
(OFF IS > 2.4V,
ON IS '-'

ifi
<3

~

~

70

VIN

i/

60

~I

II11111

=5V, MAX734

50
40
30

• 170kHz fixed-frequency oscillator
• Current-mode PWM

./

20

100~A

1mA
10mA
LOAD CURRENT

• 70JlA shutdown mode
• a-pin

so package (MAX734)

• 1.23V reference output

100mA

Figure 96. Efficiency vs. Load Current

• Soft-start circuit
• Evaluation kits available

INPUT

_ _ _ _ _ _ _ _Re'ated Data Sheet

+

2 VREF

_______ App'ication Discussion
12V at 120mA is a common design requirement for
portable computers, as this is the power required to
support Vpp (peripheral and programming voltage) for
two PCMCIA card sockets. This circuit provides a tiny
solution, with a core size requirement only half that of
competitive devices (18JlH vs. 33JlH) due to a relatively
high switching frequency. Clean, PWM fixed-frequency
switching ensures low-noise input ripple current
characteristics so as not to pollute the system +5V bus
with random noise.
The MAX734 DC-DC regulator IC used in this circuit
contains a current-mode PWM controller and 2A power
MOSFET. The regulator is digitally controlled through its
shutdown (SHDN) pin. When low, SHDN disables the
device and reduces the supply current to 701lA. In this
inactive state, the series-DC connection of inductor and
rectifier places Vpp at the level of VIN minus the fOlv'lard
drop of the rectifier diode.
Because this low level of Vpp (approximately 4.7V)
cannot program a flash memory device, there is no need
for an extra switch transistor that disconnects the output
completely. When SHDN goes high, the PWM begins
switching and drives Vpp to 12V with in 1.5msec.
Efficiency is greater than 85% over most of the load
range.
~~)(I~

33flF

::c 16V

• MAX73412V Boost Regulator

ON/Off
(OFF IS < 0.25V,
ON IS>2V)

LXI-'6_.--t\b_ _~ +12V
OUTPUT

V+

1 SHDN

GND 5

AIIAXIM

MAX734

=

+

::c

3 SS

33flF
16V

0.001ftf
L1= SUMIDA CD43-1BO (3.5mm HEIGHT)

Figure 97. 5V to 12V PWM Boost Regulator

Soft-start is a nice feature in situations where the 12V
DC-DC is put inside a PCMCIA memory card and in
other applications where the characteristics of the 5V
source may be unknown. With soft-start, the designer
can control the amplitude of the start-up current surge
that the circuit places on the 5V source (and avoid
tripping the system Vee power monitor/reset circuit)
simply by adding a low-value timing capacitor from SS to
GND.
The MAX732 is a high-current version of the MAX734
with slightly better efficiency. The MAX1732 is a selfcontained DIP hybrid version of this device with all
components, including magnetics, built in.

______________________________________________________________

65

5V to 12V at 500mA
______,Application Parameters
Input Voltage Range ......................................2.8V to 6V
Quiescent Supply Current (VIN = 5V) .......................30011A
Max Load Current Capability (VIN = 4.75V) ............... 500mA

90

.uuur

VIN=6V

/

80

VIN=4V_

/

~

[; 70

• Small external components

~
13

• Pulse-skipping PFM

~

60

• 1.5% reference output
50

• 30ILA shutdown mode

~

I

40
100~A

_ _ _ _ _ _ _ _ Related Data Sheet

1mA

10mA

100mA

1A

LOAO CURRENT

• MAX721 Palmtop SMPS
Figure 98. Efficiency VS. Load Current

______-"Application Discussion
Normally, the MAX?21 controller Ie in this 12V boost
circuit is meant to operate from 2 AA cells. However, it
leads a secret life as a general-purpose boost controller,
here pressed into service with a 5V input. If a larger
MOSFET is used to increase the output power capability,
buffer 012 with a MOSFET driver (the driver within the
MAX?21 is not intended to drive MOSFETS with more
than 15nC total gate charge).
The MAX?21 is amazingly tolerant of bad construction
technique and poor-quality components, since it is a
pulse-skipper and therefore doesn't require a large pole
at the output for loop stability. Ultimately, this means that
the circuit can be made physically smaller than PWM
counterparts, with no risk of bad transient response or
output overshoot. Low-frequency noise in the output
ripple waveform is the trade-off. If a fixed-frequency
PWM solution is needed, use the MAX? 41.

ONIOFF

+--t!l'-1>--------'i+,:.::12c:,.VOUTPUT

l1 =SUMIDA CD75-220
Q1 =1/2 SILICONIX Si9942

Figure 99. 5V to 12V Medium-Power PFM 800st Control/er

66 _______________________________________________________________

~A)(I~

5V to 12V with Micropower
Shutdown Mode
______Application Parameters
Input Voltage Range ........................................ 4V to 7V
Quiescent Supply Current (VIN = 5V) ....................... 1.3mA
Max Load Current Capability (VIN = 4.5V) ................ 120mA
Start-Up Rise Time .........................................1.5msec

100

C
(;

15

*

• 61lA shutdown mode
• 170kHz fixed-frequency oscillator

80

r-JINI=' ciJ~ 1~AX7~4

70

,;

--

/

60

13

50
40

• Current-mode PWM

30

• 1.23V reference output

20
100~A

• Low surge current on start-up

_ _ _ _ _ _ _ _ Related Data Sheet

II IIIII

90

lmA
lOrnA
LOAD CURRENT

100mA

Figure 100. Efficiency vs. Load Current

• MAX734 12V Boost Regulator

______~Application Discussion
To be truly micropower, the supply current of a switching
regulator should be down at the level of the battery selfleakage current (typically 20llA or so) or less. Boost
regulators in general are difficult to shut down
completely because of the series connection of inductor
and rectifier, which forces the output to VIWVDIODE' Even
if the load is not drawing current, the regulator's own
feedback resistors act as a load.
Figure 101 shows a boost regulator using an external
P-channel power MOSFET as a high-side load switch,
which enables the standby current to be cut to 61lA
typically. The MAX734's connection to the feedback
resistor divider (V OUT) is on the output side of the load
switch, and is therefore disconnected when the circuit is
shut down.
The MOSFET switch provides an unexpected bonus: It
can be used as part of an RC filter to eliminate highfrequency switching noise. This filter consists of the
switch's rDS(ON) and an optional 0.11lF ceramic capacitor
from the output to ground.

INPUT
(OFF IS < O.25V.
ON IS > 2V)

ON/OFF

33~Fi
8

1_
SHDN

--1.

V.

-

VREF

.

VOUT

-1.

SS MAX734 LX

...i

CC

!....6

GN°i

~ L1

I

18~H

1NS.B,.17

OUTPUT
SWITCHED
Ql .12VAT120mA

.I.h~
-'01

33~F
16V

-=-

±'' '

lOOk

-=-

O.OOl~F

II

I
I
L1= SUMIDA CD43-180MC
Ql = SILICONIX Si9400DY
Q2=2N7002

Q2

-=-

Figure 101. 5V to 12V Boost Regulator with Micropower Shutdown

67

3.3V to 1.2Vat SOmA
______Application Parameters
Input Voltage Range •••..••••.••.••••••••••.••••••••••••.•• 2V to 12V
Start-Up Supply Voltage (ILOAD = 0) .......................... 2.2V
Quiescent Supply Current (VIN = 3.3V) ...................10.3mA
(VIN = 5V) ..........................6mA
Shutdown Supply Current ......................................35~
Max Load Current Capability (VIN = 3.0V) ..................80mA
(VIN = 2.0V) .................. 40mA
Start-Up Rise Time ............................................4msec

100

IVI~~W

90
i"'"

80

C
>u
zw

u
tE
w

-;:...- ..-viN =3.3V

70

.1.11111
VIN =2V

60
50

/

40
30

V
V

t:-

20

• Small 8-pin SO package

lOrnA
LOAD CURRENT

lmA

• Tiny 3mm diameter inductor

100mA

• 170kHz fixed-frequency oscillator
• Current-mode PWM

Figure 102. Efficiency vs. Load Current

• Soft-start pin
• 1.23V reference output
INPUT

_ _ _ _ _ _ _ _Related Data Sheet
• MAX734 12V Boost Regulator

_______,Application Discussion
This circuit is bootstrapped, meaning that the supply
voltage for the switching regulator is derived from the
output rather than the input. A path from input to output,
vital to initial start-up, is provided by the series
connection of inductor and diode common to all boost
regulators. If a 5V supply voltage is available in the
system, it is best to power the MAX734 from it rather than
the 12V output to minimize losses due to the device
supply current. See the 2-3 Cell to 3.3V/5V, 12V, and
-18V: A System Solution circuit for an example. This
circuit will not start up under loads greater than 10mA,
which is not usually considered a problem in flash
memory applications, because virtually no Ipp current is
drawn until the erase or write command is given.
Operating supply current can be reduced by adding a
2.7kQ resistor in series with V+. This resistor drops the
supply voltage to the Ie thereby reducing current flow
due to the MOSFET gate charge.

(OFF =2V)
ON/OFF

V+ 8

1 SHDN

2 VREF

~

..L

3 SS

VOUT 7

~ LXJ-=6_-t-.....*_-+_+12V

OUTPUT

I

47~F

I

l6V _

O,OOl~F

L1 = SUMIDA CD43-1 00
PLACECl DIRECTLYFROMV+ TOGND

Figure 103. Bootstrapped, Low-Voltage, + 12V-Output Boost
Regulator

68 _ _ _ _ _~_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

AIIAXLM

2·3 Cells to 12Vat 60mA
______,Application Parameters
90

Input Voltage Range ...................................0.9V to 5.5V
Start-Up Supply Voltage (ILOAD =0) ••••.•.•••••••.••.•.••.••• 1.4V
Quiescent Supply Current (VIN = 3V)
Main SMPS = 5V •.••.••.•.•.••• 1401lA
Both SMPS ..••••.•.••.••.••••.•• 5001lA
Max Load Current Capability (VIN = 3V)
Main SMPS = 5V .•.•••.•.•• 400mA
Auxiliary SMPS =12V .•.•. 120mA

VF;

§:
~
zw
U

...

• Power-fail detection
• Evaluation kit available

_ _ _ _ _ _ _ _Related Data Sheet
• MAX718 PaimtopSMPS

'"

II~BA,.'r~ jJ
1111

70

~
60

50

I III

VBATT.2V

VI
VI
'j
1001lA

IIIiOUT i 112'11
1mA

lamA 100mA
LOAD CURRENT

• Pulse-skipping PFM
• O.5MHz switching frequency
.1.5% reference output (alive in shutdown)

VBATT·5V

80

• Dual regulated outputs
• Accepts three input sources

IIII 1L

r""

Figure 104. Efficiency VS. Load Current (5V mode)

-+------------------

MAIN BATTERY
INPUT
lSIlJ!F:r:

MAIN
OUTPUT _ _~I--4I--FI
3V/5V

C512 11

AIIAXIAII
7

_______Application Discussion
Getting 12V at 1W from a battery that can be less than 2V
(asin 2-cell applications) is trickier than it sounds. Peak
currents can exceed 1A due to the high voltage step-up
ratio, and can really hammer small high-impedance
batteries unless filtered properly. Commercially available
power MOSFETs won't even switch with gate-drive levels
less than 2V. The choice: Use creaky old bipolar
transistors with attendant frequency limitations due to
stored base charge (read: big inductors and capacitors)
or find a way to get adequate gate drive for start-up. This
circuit solves these problems by operating at a high
frequency to improve filtering and by deriving the gate
drive for the 12V SMPS from the main 3V/5V SMPS.
This medium-power palmtop supply can generate 3.3V
and 5V, 3.3V and 12V, or 5V and 12V, depending on the
state of certain logic control inputs. Two regulated output
voltages are generated from one of three input voltage
sources: an AC-OC wall-cube adapter (7V to 20V), a main
2- or 3-cell battery, or a lithium backup battery. The
dotted-line connection at the top of L2, which powers the
auxiliary supply, is normally hard-wired to the main
battery, but can also be connected to the main output
when power comes from the AC wall adapter. The main
switching regulator automatically shuts off to save the
batteries when the AC-OC wall cube is plugged in.

..MAXI..M

MAX718

+--_*_-'-ILXB

=

1N4001

FB12 1-'10,,--_ _ _--,
PFO r9_ _•

3_ _ _ CONTROL
3/5 ..
I/Os

BKUP 1
2_ __
120N ..

12/5 ....41--_ _

Q1 • MOTOROLA MTD3055EL
OR 1/2 519942
L1. L2= SUMIDA CD54-220

=

Figure 105. 2-3 Cells to 3V/5V and 5V/12V: A System Solution

The two switch-mode supplies are the same type as
found in the MAX756, which has a wide range of
maximum switching frequencies. Practical inductor
values are from 51lH to over 200llH, allowing one to trade
off switching losses and physical size. Lower inductance
values increase frequency without affecting peak
currents or load current capability significantly.
Inductance values can be increased for lightly-loaded
applications, in order to reduce peak currents .

69

PCAfCIA Power Switching Network
_ _ _ _ _ _,Application Parameters

C1 =GND
AVpP1

AVppo

0

0

AVpp= OV

0

1

AVpp= VeelN

1

0

AVpp = VPP1N

1

1

AVpp = High-Z

BVpP1

BVppo

0

0

BVpp = OV

0

1

BVpp = VeelN

• Two 0V/3.3V/5V high-side Vee switch controllers

1

0

BVpp = VPPIN

• Latched or transparent logic interface

1

1

BVpp = High-Z

Quiescent Supply Current. .. .................................. 350J,1A
Shutdown Supply Current ......................................10J,1A
Max 12V Load Current Capability (each output) ......... 100mA
Vpp Switch On-Resistance ....... .................. ,. '" ..... .. 1.60
• Shrink small-outline package (SSOP)
• Two OVNecJ12V switched Vpp outputs

RESULT

RESULT

• Vpp valid detection comparators
• 1.25V reference output
• Meets PCMCIA Rev. 2.0 specs
• Compatible with standard PCMCIA controllers:
Intel 82365SL-DF
Cirrus CL-PD6720
Fujitsu MB86301

_ _ _ _ _ _ _ _ Related Data Sheet
• MAX780 PCMCIA Switch

________Application Discussion
In September 1991, a standard for removable memory
cards was adopted in preliminary form by an association
of portable computer and memory card manufacturers.
PCMCIA (Personal Computer Memory Card Intemational
Association) PC Card release 2.0 sets the Vpp
(programming and peripheral voltage) and VCC power
requirements for flash memory cards and other types as
well, such as SRAM, DRAM, EPROM, EEPROM, and OTP.
Figure 90's circuit integrates the power switching
functions needed for two PCMCIA card sockets in a host
computer.
The 12V outputs are capable of sourcing 100mA per
socket in the 12V state, allowing for 16-bit-wide flash
programming (30mA/chip). In the 5V state, the maximum
load requirement drops to 2mA, which is the worst-case
power drain of the non-flash-type EEPROMs that need 5V
Vpp programming voltages. Therefore, the PCMCIA
circuit needs a strong 12V switch, but can get by with a
weak device for the 5V state. The OV state is needed in
order to prevent "hot insertion," where someone would
plug a card into a socket connector with live power,
possibly causing loss of data retention.
Discrete N-channel MOSFETs perform the VCC output
switching. OV/3.3V/5V switching action may require an
extra series MOSFET in the path from +3.3V to VCC (see

C1 =GND
AVCC1

AVcco

RESULT

CARD MODE

0

0

ADRV3=GND
ADRV5 = GND

Card A Vee = OV

0

1

ADRV3 = High-Z
ADRV5= GND

Card A Vee = 3.3V

1

0

ADRV3=GND
ADRV5 = High-Z

Card A Vee = 5V

1

1

ADRV3=GND
ADRV5 = GND

Card A Vee = OV

BVCCl

BVcco

RESULT

CARD MODE

0

0

BDRV3 = GND
BDRV5 = GND

Card B Vee = OV

0

1

BDRV3 = High-Z
BDRV5 = GND

Card B Vee = 3.3V

1

0

BDRV3 = GND
BDRV5 = High-Z

Card B Vee = 5V

1

1

BDRV3 = GND
BDRV5 = GND

Card B Vee = OV

Figure 106. MAX780 Truth Tables

the MAX780 data sheet) in order to prevent hot insertion
caused by the path through the MOSFET body diode.
Note: This PCMCIA switching function can be achieved at
much lower cost with an integral power supply solution
such as the MAX782 or MAX783. See 6-12 Cells to 3/3\1,
5\1, and 12Vat High Power: MAX782 Dual Buck Controller.
Also see the stripped-down versions of the MAX780A
(B,C, and D suffix) as well as the single-channel and dualchannel versions (MAX614 and MAX613).

70 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

..NI..AIXI..NI

PCMCIA Power Switching Network

+SV
INPUT

+12V
INPUT

+3.3V
INPUT

+ 3.311f

T

1 C2
2 C1

3Wii

VCCIN 1-'2;::.2_ _ _- - 1 - - - - ,

1-_ _ _ _ _ _ _=_--14 AVPP1

AVPPt'2'-'.1-----t--_H--'
S
BVPP,,2"'0_ _ _ _ _-t-_ _H--,
1---------,AVPPOaor
19
6
REf
1 - - - - - - - - - , BVPP1
SHON 18
1-_ _ _ _ _ _ _ _~7 BVPPO
I-'-'------t---.
AGPI 17
8 AVCC1
f-________"-I
BGPI 16

VPP1
VPP2
VCC
SLOTA

1-_ _ _ _ _ _ _ _ _,9 AVCCO
AORV3,,1o=.S--t-t---t--t-r-----I

1-_ _ _ _ _ _ _ _1,0 BVCC1
11

1 - - - - - - - - - ' - ' - 1 BVCCO

VPP1

AORVS 14
BORV3 13

12 BORVS

VPP2
VCC
SLOTB

ALL RESISTORS = 1M
ALL TRANSISTORS = 1/2 Si99S6

Figure 107. PCMCIA Switching Network

71

Section 9
Miscellaneous Circuits
Low-Dropout Linear Regulator with External PNP and Diode-OR'ed Output
High-Side Current-Sense Amplifier: ICL7612
N-Channel High-Side Power Switches: MAX620 Charge Pump
System Voltage Monitor: MAX8214 Quintuple Detector

~~I~

____________________________________________________

73

Low-Dropout Linear Regulator with
External PNP and Diode-OR'ed Output
______App'ication Parameters
Input Voltage Range ..................................5.4V to 16.5V
Quiescent Supply Current (VIN = 10V) .......................201lA
Max Load Current Capability (VIN = 6V) ...... , .......... .. 500mA
Dropout Voltage (ILOAD = 100mA) ......•.....•.......•...••400mV

100

11111

90

C

II

VIN=5.5V

80

v

70

t
• 5j.LA shutdown mode

60
a'i
c:;

• Low-battery detect comparator

iE
w

50
40

_ _ _ _ _ _ _ _Re'ated Data Sheet

111111

10
10~A

_______App'ication Discussion

VIN = 12V

IIIIII II

20

• MAX666 Linear Regulator

This linear regulator circuit is useful for uninterruptible
battery-backup applications as well as for low-power
circuits that use batteries for main power and optionally
take power from wall-cube type AC adapters. The main
advantage of this circuit over monolithic IC linear
regulator solutions is that the pass transistor is external
and can be sized appropriately to handle the required
power dissipation. If the power dissipated is low enough,
the MAX666's internal SOmA power transistor can replace
the 2N2905. The MAX667 should also be considered in
these cases, because it has a bigger (2S0mA) pass
transistor and lower dropout voltage.
The MAX666 IC works well as a controller of external PNP
transistors and has very low quiescent supply current.
This circuit, although shown with a boost converter to
provide the auxiliary power input, could just as easily be
powered from a buck regulator or a second linear
regulator.

~

V

30

100~A

II

1mA
10mA
LOAD CURRENT

100mA

Figure 108. Efficiency VS. Load Current

INPUT

-

1 SENSE

VIN 8

2 VOUT

LBO 7

+5V
-t--.--.......-""OUTPUT

-+

3 LBI MAX666 VSETp6_ _
4 GND

SHDN 5

BOOS~

REGULATOR

Ie

Figure 109. Low-Dropout PNP Linear Regulator with Diode OR'ed
Output for Battery Backup

74 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

.AIIAXI.AII

High-Side Current-Sense Amplifier
______Application Parameters
Input Voltage Range ....................................4.5V to 48V
Quiescent Supply Current (VIN = 5V) ......................... 201JA
Gain Factor .................................................... 1V/Amp

VSUPPLY (V) RZ (Q)

+5

+ Senses current in the battery positive lead
+ Requires no precision resistor network

+9
+12
+24
+48

_ _ _ _ _ _ _ _ Related Data Sheet

120k
320k
470k
1.1M
2.2M

+ICL7612A Micropower Op Amp

_______,Application Discussion
This op-amp circuit senses current in the positive battery
lead, allowing the battery negative terminal to be directly
connected to circuit ground. The output is a ground referenced output voltage directly proportional to the
current flowing in the low-value sense resistor. The
output voltage is typically applied to the input of an AID
converter or integrating V/F converter. Since the 10
terminal is a true current source, it can be referenced to
any level within the supply rails.
The main advantage of this circuit is that it does the job of
an instrumentation amplifier without needing the precision
resistor network that differential amplifiers usually require.
The ICL7612A's common-mode input voltage range
includes its own positive supply rail. Feedback via the
small-signal JFET forces the voltage across R1 to equal
the voltage across the sense resistor. The current through
R 1 must flow to the output. So, the value of R 1
determines the transconductance 10NSENSE. R1 should
be kept in the range of 100 x RSENSE to 1000 x RSENSE.

Figure 110. Limiting Resistor Selection Table

RSENSE
VSUPPl y __--~'V0.'Vln\rl---_ _--"'llO::.::AD:....--___.

LOAD

VOUT
lN4148

RZ _ VSUPPl Y- 2.5V
20~A
VOUT=llOADxROUTX

~
Rl

Figure 111. Micropower Positive Supply Current Monitor

75

N-Channel High-Side Power Switches
______Application Parameters
Input Voltage Range ..................................3.SV to 16.SV
Quiescent Supply Current (VIN = SV) ......................... 7DIJA
Maximum Load Current (each switch) ..........................SA

ifJV
+fN
O.047~F

• Regulated charge-pump supply:
VGATE = (VBATT + 11V)
• Undervoltage lockout
• Power-ready detection
• Latched or transparent logic interface

_ _ _ _ _ _ _ _ Related Data Sheet
• MAX620 High-Side Charge Pump

_______ Application Discussion

Figure 112. Quad High-Side Power Switch

This circuit provides four high-current MOSFET load
switches for power management. The MOSFETs are Nchannel source-followers for minimum rOS(ON)' To turn on
each switch, the MOSFET gate is forced 11V above the
battery by the MAX620 micropower charge-pump
regulator.
This family of charge-pump, high-side power supplies
offers numerous devices, including devices with internal
pump capacitors and internal N-channel MOSFETs, as
well as a single stand-alone 8-S01e power-supply chip
(MAX622).

76 _ _ _ _ _ _ _ _ _ _ _~_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

..MAXI..M

System Voltage Monitor
_ _ _ _ _~Application Parameters
Input Voltage Range (monitored voltage) ....... 1. 25V to >1 DDV
Input Voltage Range (IC only) ......................... 2.7V to 11V
Quiescent Supply Current (VIN = 5V) ......................... 16!lA
Threshold Accuracy Error (TMIN to TMAX) ..............±1% Max

24

TA~-5~'C

22

<20
t-

TA= +25'C
20

W

• 1.25V, 0.75% reference output
• Built-in hysteresis

a:
a:

18

:::J

'-'

::;

16

(J)

14

DD:::J

,/

v.: ~
IJ,/
,p

V~ ~

Z

• Five precision comparators plus reference

/

,~

~ ,/

V

TA= +125'C

12

_ _ _ _ _ _ _ _ Related Data Sheet
• MAX8214 Voltage Monitor

10
1 2

3 4 5 6 7 8 9 10 11 12
SUPPLY VOLTAGE (V)

Figure 113. Supply Current vs. Supply Voltage

______~Application Discussion
Large, portable systems often require several voltage
monitoring comparators to detect the status of main and
backup batteries as well as for power-fail monitoring and
AC adapter detection. This circuit fits that socket nicely,
while burning only 311A per comparator and providing
good threshold accuracy plus built-in hysteresis.
Other similar circuits include the ICL7665A dual voltage
monitor, MAX8211 and MAX8212 single voltage
monitors, and the ultra-low current MAX912 (basically, a
single version of the MAX8214, but with high output drive
capability). There are also two versions having internal
divider resistors for preset trip voltages (MAX8215 and
MAX8216), and a version with open-drain outputs
(MAX8213).
Another useful IC is the 2.5V low-dropout MAX872
reference, a three-terminal type that consumes 1O~A
and operates from supplies as low as 2.7V. The MAX872
can be connected to any external comparator to create
a precision voltage monitor.

MS

Voo

GND

IN1

>---t-"'=t- FULL CHARGE
BACKUP

>--t-"'!.!..:!.J-- BAIT DEAD

~=+""1.25V

Figure 114. Precision Multiple Comparator with On-Chip Reference

~A)(I~

________________________________________________________

77

Appendix A
Switch·Mode Design Equations
...
There are literally thousands of design equations for switch-mode power supplies. These
equations, most of which are of only academic interest to the system designer, could easily fill
several books. Instead of throwing reams of such equations at the reader, only a few key equations
are included here, hopefully revealing more forest than trees.
Key parameters to be calculated include duty factor and the critical point, so the designer knows if
the converter is operating in the discontinuous-conduction mode (inductor current returns to zero
each cycle) or continuous-conduction mode (with a DC offset current built up in the inductor).
The equations also describe the relationship between inductor value and peak current; once
these are known, the most important specifications for external components become known. For
example, knowing the inductor value and peak current allows one to specify the inductor's
saturation current rating, as well as the peak current rating needed for any external switch
transistors and rectifiers.
Note: The equations for fixed-time PFMs produce impossible results if the circuit is assumed to be
operating in discontinuous mode when in fact the input-output voltage ratio and on-timejoff-time
ratio force the circuit into continuous mode. Check the critical point first.

~AXI~

__________________________________________________________

79

800st Topology

!

OPERATING
CONDITIONS
I

Discontinuous
Mode

Critical Point
(Crossover)

Continuous
Mode

PFM
(CURRENT-LIMITED)

PWM
- f2IwT(VOUT +vo-\lN)
jl

PEAJ(~

Duty Cycle = jl(\.w) x100'k
\IN -Vsw

IOUT(CIIITICAl)

_ (VOIlI + Vo - \IN)(V1N)2
2jl(VOUT + VoJ2

~ = (\IN-Vsw)TON
l
Imm
(IIIH - Vii'!!)2 (TQ~)2
MAX) - 2l(Vour + Vo - VIN)(ToN + TOFF )

l(CllmCAl)

_ (VmJT +vo - \IN + Vii'!!)(TOFF)
~MIT

~ = ~(VOUT + Vo) +
\IN -Vsw
(VIN- Vii'!!)(VOUT + Vo - ~N)
2jl(VOUT + Vo)

~ =~MIT
~UT(MAX) =

Duty Cycle =VOIlI + Va - \IN X100'k
VOUT +Vo

Duty Cycle _ VDUT + Vo - \IN X100*.
VDUT+VO

-_._--

-_.-

------_._._--

(~IMIT - (VQIII + Vo - \IN)TQFF )( \IN - Vsw )
2l

--

-----

VOUT+VO

PFM
(FIXED-TIME)
~ = (\IN - V9N )TON
l
~
_ (VIN - V9N)2(TON)2 j
UT(MAX) - 2l(Vour + Vo - V
IN )

Duty Cycle = VDUT + Vo - \IN X100'k
(Critical)
Vour + Vo

Operation of fixed-time PFMs In the continuous
mode is unpredictable due to the lack of current
limiting and usually not recommended.
Continuous condJctlon In fixed-dme PFMs does
not depsnd on load current only on
inpuVoutput vottage redo. If the clrcu~ has a
maximum dUly cycle capability that exceeds
critical duty cycle, continuous mode results.
Most flxed-time PFM ICs have fixed 50% duty
cycles.

Boost Topology (continued)

'.

~

•

+

O~GE
:~~:
INDUCTOR CURRENT

VOUT~. ---------VIN·-

o-

BOOST TOPOLOGY SCHEMATIC

-

---

-

--

---

---

SWITCH VOLTAGE

DISCONTINUOUS WAVEFORMS

~-GATE VOLTAGE
IPEAK __~

-----------------------INDUCTOR CURRENT
VOUT

-r--rT--n---n----

__ ~_L--J__~_~ __
SWITCH VOLTAGE

CONTINUOUS WAVEFORMS

!!!

:a

Buck Topology

OPERATING
CONDITIONS
I

-

V. )
121 OUT (V,IN _ V,SW _ VOUT )111
\ 'OUT + 0

Discontinuous
Mode

jl("'N + Vo)
jl(l )
Duly Cycle
PEAK
x10(J'k
"'N - Vsw - VOUT

Critical Point
(Crossover)

I
_ (VOUT + VOX"'N - Vsw - VOUT)
OUT(CRITICAl) 2jl("'N)

•

Continuous
Mode

PFM
(CURRENT-LIMITED)

PWM
I

PEAK

(V,IN - V,SW - V.OUT )TON

l

(V,

PEAK -

V(\/,- V, - v. )
IpEAK = lOUT + OUT IN sw OUT
2jl(l,\N)
V V,
DulyCycle= OUT+ 0 x10(J'/o
V, - V,

IN

sw

I
_
OUT(MAX) -

V,

)

PFM
(FIXED-TIME)
I

PEAK

(V,IN - V,SW - v.OUT )1:ON

l

(V,

v

)

IN; OUT +1 "'N-VOUT)(ToN ?
IN; OUT +1 VIN-VOUT)(ToN)2j
OUT
I
_l-~OU~T_-<.._ _ _ __
2l(Toff + TON)
OUT(MAX) 2l

l
(CRITICAl)

I =I
PEAK LIMIT
IOUT(MAX) = IliMIT

(VOUT + VO)TOff
IliMIT

(VOUT + Vo )TOff
2l

V. +V
Duty Cycle = ....Q!!L....Q. x 100%
"'N - Vsw

Duty Cycle (Crilical) = VOUT + Vo x10(J'/o
"'N - Vsw

Operation of fixed-time PFMs in the continuous
mode is unpredictable due to the lack of current
limiting and usually not recommended.
Continuous conduction in fixed-time PFMs does
not depend on load current, only on
inpuVoutput voltage ratio. If the circuit has a
maximum duty cycle capability that exceeds
critical duty cycle, continuous mode results.
Most fixed-time PFM ICs have fixed 50% duty
cycles.

Buck Topology (continued}

•

+

-~GATE VOLTAGE
:EA~~
INDUCTOR CURRENT

::UTrT~--n-~--n~---~~--~
o :=~~~=~SWITCH VOLTAGE

BUCK TOPOLOGY SCHEMATIC

DISCONTINUOUS WAVEFORMS

o ~-----GATE VOLTAGE
IPEA~__

-----------------------INDUCTOR CURRENT

lOIillLo ---

SWITCH VOLTAGE

CONTINUOUS WAVEFORMS

~

:

Inverting Topology

OPERATING
CONDITIONS

Discontinuous
Mode

Critical Point
(Crossover)

PWM
~ _ !2IoUT(VoUT + Vo)
EAK jL
Duty Cycle =jL(lPEAd x 100'10
VIN -Vsw

IOUT(CRITICAl)

~EAK

Continuous
Mode

PFM
(CURRENT-LIMITED)

PFM
(FIXED-TIME)

I - (~N - VSW)TON
PEAK L
I
_ (~c VSW )2 (TON)2
OUT(MAX) - 2L(VOUT + VOXTON + TOFF )

I - (~c VSW)TON
PEAK L
(~N - Vsw )2 (TONf j
IOUT(MAX)
2L (VOUT + Vo)

7

(~N)2

(~N - Vsw XVOUT + Vo + \IN) +

2jL(VOUT + Va)
IOUT(VOUT + Vo + ~N)
~N -vsw
VOUT +Vo
X 100'10
Duty Cycle
~N - Vsw + VOUT

VOUT +Vo
Duty Cycle
x100'1o
(Critical) ~N - Vsw + VOUT

L(Critical) =(VOUT Vo )(TOFF )
LIMIT

2jL(~N + VOUT)2

Operation of fixed-time PFMs in the continuous
mode is unpredictable due to the lack of current
limiting and usually not recommended.
Continuous conduction in fixed-time PFMs does
not depend on load current, only on
inpuVoutput vo~age ratio. If the circuit has a
maximum duty cycle capabil~ that exceeds
critical duty cycle, continuous mode results.
Most fixed-time PFM ICs have fixed 50% duty
cycles.

IpEAK =IliMIT• IOUT(MAX) =
(lliMIT

(VoUT+Vo)ToFF
2L

Duty Cycle

X ~cvsw

VOUT +Vo
~cVSW+VOUT
--

)

VOUT + Va + \IN
x 100'10

-----

-

--

Inverting Topology (continued)

O-~ViiLTAGE
:EA~~~::::::::::
INDUCTOR CURRENT

•

•

•

+

VIN

o

rI~:tUk:----

_~~ll ___

Your ---

INVERTING TOPOLOGY SCHEMATIC

---

u____U__

----swiTCH-VOLTAGE

DISCONTINUOUS WAVEFORMS

-~--GATE VOLTAGE
IPEAK_~

__

INDUCTOR CURRENT

VIN

-==++=rr==rr----~~~_U __1J __ U_

Your -----

--

--S-WITCHVDLTAGE

CONTINUOUS WAVEFORMS

g:

Appendix B
Abbreviation Glossary
AA-size cell (ANSI type 15A, usually alkaline)

AA -

ABPTS -

"Atomic batteries to power ...
Turbines to speed ... "

analog-to-digital converter

ADC -

nickel-metal-hydride

NiMH -

PCMCIA -

Personal Computer Memory Card
International Association

power dissipation

Po -

I

CCFT -

cold-cathode fluorescent tube

DAC -

digital-to-analog converter

DCR -

DC resistance

DPAK -

TO-252 surface-mount power package
effective series resistance

ESR -

PFET -

P-channel power MOSFET

PFM -

pulse-frequency modulation
power-supply rejection ratio

PSRR -

pulse-width modulation

PWM rOS(ON) -

f- switching frequency

RTC -

HP - high-power

SMPS -

ILIMIT -

peak current-limit threshold

lou,.- output (load) current

on-resistance, drain to source

real-time clock
switch-mode power supply
surface-mount type

SMT SSOP -

shrink small-outline package (fine lead pitch)

IpEAK -

peak current (inductor, switch)

TA -

JFET -

junction field-effect transistor

TOFF - off-time

L -inductance value
LCD -

liquid-crystal display

LDO -

low dropout

Li- Lithium
LP -

low-power

Mux - multiplexer
NiCd -

nickel-cadmium

NFET - N-channel power MOSFET

~A)(I~

ambient temperature

on-time

TON -

Vo -

diode forward voltage (typ O.4V)

VF -

forward voltage

V 1L-

logic input low voltage

V1H - logic input high voltage
VLSI Vpp -

VSW -

very large-scale integration
peripheral and programming voltage
switch transistor forward voltage (typ O.2V)

____________________________________________________________

87

AppendixC
Surface-Mount Component Suppliers
Component

~e

Inductors
Low-value resistors
Tantalum capacitors
Ceramic capacitors
Rectifiers and MOSFETS
MOSFETS
Tantalum capacitors
Inductors
Inductors
Transistors
Transistors and MOSFETS
Inductors
Inductors
Inductors
Inductor Cores
Tantalum Capacitors (TPS)
Electrolytic Capacitors (OS-CON)

Company
Coiltronics
IRC
Matsuo
Murata-Erie
N.I.E.C.
Siliconix
Sprague
Sumida

TDK
Zetex
Motorola
SAEPOWER
Gowanda
Inductor Supply
Magnetics, Inc.
AVX
Sanyo

_________ Construction Notes
Many of the switch-mode supplies given in this book
operate with high frequencies and have large peak
current levels. Careful component selection and board
construction is mandatory for high-frequency SMPSs.
Use etched PC boards with a continuous ground plane
where practical; failing that, use a copper-clad board
with traces cut by exacto-knife or razor blade; failing that,
use a breadboard with soldered-in point-to-point wiring.
Breadboard materials with pre-etched DIP solder pads
are excellent for prototyping, even for surface-mount
components (you can use the DIP pads as lands for the
surface-mount components). Plug-in plastic protoboards
and wire-wrap techniques are absolutely unacceptable. .
In high-power circuits, trace out the high current paths on
the schematic and keep these paths short when doing
the wiring. This is especially true for the ground; keeping
~~)(I~

Factory FAX
[country code1
[1] 407 241-9339

[1] 213722-9028
[81] 6-331-1386
[1] 404736-3030
[81] 3-3494-7414
[1] 408727-5414
[1] 508 339-5063
[81] 3-3607-5428

[81] 3-3278-5358
[44] 61 6275467
[1] 408 986-8529

[1] 716532-2702
[1] 714 978-2411
[1] 412282-6955
[1] 8036263123
[81] 0720 701174

USA Phone
(407) 241-7876
(213) 772-2000

(714) 969-2491
(404) 736-1300
(805) 867-2555"
(408) 988-8000
(508) 339-8900
(708) 956-0666
(708) 803-6100
(516) 543-7100
(602) 244-6900
(408) 987-2700

(716) 532-2234
(800) 854-1881

(412) 282-8282
(803) 448-9411

(619) 661-6835

the high-current ground paths short wins 90% of the
layout battle.
Except for micropower circuits, inductors and capacitors
must be high-quality types intended for switchingregulator applications. See the table above. Usually, the
stuff found at the local electronics junk store is garbage
(iron-core chokes, standard aluminum electrolytic
capacitors, etc). Plan for at least 2-3 week lead times to
acquire the samples you need to do a good design.
For high-power applications, good capacitors are critical,
Four reliable vendors are:
• Sprague - 5950 series SMT Tantalum
• Sanyo - OS-CON type electrolytic
• AVX - TPS series SMT Tantalum
• Nichicon - PL series aluminum electrolytic

_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __

89

AppendixD
Power-Supply Product Selection Guide

.MAX•.M _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

91

______________________________ PowerManagementSuppHes
Part
Number

Input Voltage
Range

Linear
Output
Voltage

Quiescent Supply
DC-DC Output
Voltages

Auxiliary
Outputs

Over Temp.
(IJA)

EV Kit

Temp.
Ranges

Package
Options'

M

M

M

M

5.05 to II

2at+~ V

-5 to -26 adi. LCD
driver

N/A

200 per enabled
output line

C,E,M

DIP,SO

5.05 to II

3 at +5V

-5 to -26 adi.

DIP,SO

5.05 to II

4 at +5V

-5 to -26 adj.

200 per enabled
output line
200 per enabled
output line

C,E,M

MAX716

-5 adj.,
+ 12 or +15 adj.
-5 adj.,
+12 or +15 adj.

C,E,M

DIP,SO,
SSOP

MAX717-721

0.9 to 5.5
(battery),7 to IS
(Plug-in adapter)

N/A

+3.3 (MAX717),
+5 or +12 (all)
+3.3 or +5 (MAX7ISn20),
+3.0 or +5 (MAX719n2l)

MAX7221723

N/A

+3.3 or +5 (MAX722)
+3 or +5 (MAX723)

MAX7S1

0.S5to 5.5
(battery),7 to IS
(p\1Jg,in adapter)
5 to IS

3.3 at 10mA
5.0 at 25mA

3.3, 14, battery charger

MAX782

5.5 to 30

3.3 at 5mA
5.0 at 25mA

3.3,5.0,14

MAX783

5.5 to 30

3.3 at5mA
5.0 at25mA

3.3,5.0,14

MAX7S6

5.5 to 30

3.3 at 5mA
5.0 at 25mA

3.3,5.0

60,
40 shutdown

Neg. LCD
60,
(0 to -40) (all)
40 shutdown
_____
Battery charger, 100 shutdown,
current source,
750 standby,
dual VPP outputs -2mA operating
Dual Vpp outputs 70 standby,
750 per output
enabled
Dual Vpp outputs 70 standby
750 per output
enabled
N/A

Price t
1000-up

Current Max

40 shutdown
70 standby
750 per output
enabled

Yes

Yes
C,E
(MAX717MAX719)

SO

Yes

C,E

SO

Yes

C,E

SSOP

Yes

C,E

SSOP

C,E

SSOP

C,E

SSOP

Yes

Package Options: DIP =Dual-In-Line Package, SO =Small Outline, SSOP =Shrink Small-Outline Package
t Prices provided are for design guidance only and are FOB USA International prices will differ due to local duties, taxes, and exchange rates.
ttFutore product - contact factory for pricing and availability.

Features

($)

Independent shutdowns, backupbattery switchover, RESET and powerfail warning outputs
PC layout and parts list available

3.40

Independent shutdowns, backupbattery switchover, RESET and powerfail warning outputs
Built-in switchover from main battery
to plug-in adapter power, low-voltage
warning, AC detect, clock & RAM
keep-alive mini-switcher from backup
battery
Built-in switchover from main batttery
to plug-in adapter power, low-voltage
warning
High-power controller to 50W or more,
dual PCMCIA Vpp outputs, analog mux,
SPI interface
High-power dual controller to 50W or
more, dual PCMCIA Vpp outputs,
three precision voltage monitors,
High-power dual controller to 50W
or more, dual PCMCIA Vpp outputs,
three precision voltage monitors,
optimized for 6-cell operation
High-power dual controller to 50W or
more, two precision voltage monitors

5.75
5.95

4.95

4.63

tt
5.95

5.95

4.15

____________________________________ MOSFETDrivers
Part
Number

Output
Resistance
(0),
max(typ)

RlselFall
TA=+25'C
(ns max)

RiselFall
Over Temp.
(ns max)

Peak Output
Current (A)

Supply
Voltage
(V)

Package
Options'

Temp;
Ranges"

MAX4420/4429
MAX4426/4427/4428

2.5(1.5)
10(4)

30130(2500pF)
30130(1000pF)

6O/6O(2500pF)
40/40( lOOOpF)

6
1.5

4.5 to 18
4.5 to 18

DIP,SO
DIP,SO

C,E,M
C,E,M

MAX6261627/628

15(4)

30/30(1000pF)

4O/4O(1000pF)

2

4.5 to 18

DIP,SO

C,E,M

TSC426/427/428

15(6)

30130(1000pF)

60/4O(1000pF)

1.5

4.5 to 18

DIP,SO

C,E,M

MXT429
ICL7667

2.5(1.5)
12(4)

35135(2500pF)
30/30(1000pF)

70nO(2500pF)
40/4O(1000pF)

6

7.0 to 18
4.5 to 15

DIP,SO
DIP,SO

C,E,M
C,E,M

1.5

Pricet
1000-up
Features

($)

Single noninverung/inverting
Dual invening/dual noninverung/
dual mixed
Dual invening/dual noninverung/
dual mixed
Dual inverung/dual noninverung/
dual mixed
Single inverung
Dual inverting

1.71
1.61
1.49
1.06
1.67
1.12

__________________________ High-Side MOSFET Drivers
Part
Number
MAX620
MAX621
MAX625

Supply
Voltage
Range
(V)

Quiescent
Supply Current
(mA),
max(lyp)

Switching
Frequency
(kHz)

Package
Options'

Temp.
Ranges"

4.5 to 16.5
4.5 to 16.5
4.5 to 16.5

0.5(0.070)
0.5(0.070)
0.5(0.070)

70
70
70

DIP,SO
DIP
DIP

C,E
C,E
C,E

Pricet
1000-up
Features

($)

Quad high-side driver, V CC+11V output
Quad high-side driver, V CC+11V output, internal capacitors
Quad high-side switch, 4 internal 0.20 N-channel MOSFETs,
internal capacitors

3.85
5.82
9.98

Package Options: DIP = Dual-In-Line Package, SO = Small Outline, TO-_ = Can
Temperatore Ranges: C = O'C to +70'C, E= ·4O'C to +85'C, M= -55'C to +125'C
Prices provided are for design guidance and are FOB USA. International prices will differ due to local duties, taxes, and exchange rates.

DC/DC Converters
Input
Voltage
Part
Number

Range

Quiescent
Supply Current
(mAl,
max(typ)

Output
Voltage

(V)
(V)
STEP-UPISTEP-DOWN SWITCHING REGULATORS
1 to 5.5
51(3.3 or 3)1adj.
0.310(0.220)
MAX87718781879

STEP-UP SWITCHING REGULATORS
Adj.
MAX4l93
2.4 to 16.5
MAX630
2 to 16.5
Adj.
5,adj.
MAX631
1.5 to 5.6
1.5 to 12.6
12,adj.
MAX632
15,adj.
MAX633
1.5 to 15.6
5,adj.
MAX641
1.5 to 5.6
MAX642
1.5 to 12.6
12,adj.
15,adj.
MAX643
1.5 to 15.6
MAX654
1.15 to 5.6
5
MAX655
1.5 to 5.6
5
1.15 to 5.6
5
MAX656
MAX657
1.15 to 3.6
3
1.5 to 5.6
5
MAX658
MAX731
1.8 to 5.25
5
4to9.3
12
MAX732

Pricet
111OO-up

Output
{mAtyp)

Control
Scheme

Package
0l!!!0ns·

EVKit

Ranges"

Features

{$)

240

PFM

DIP.SO

Yes

C,E,M

Gives regulated output wben input
above and below the ou!J!!!!j no transformer

tt

300mW
300mW
40
25
20
300
550
325
40
60
250
60
110
200

DIP,SO
DIP,SO
DIP,SO
DIP,SO
DIP,SO
DIP,SO
DIP,SO
DIP,SO
DIP,SO
DIP,SO
DIP,SO
DIP,SO
DIP,SO
DIP,SO
DIP,SO

Improved RC4193 2nd source
Improved RC4193 2nd source
Only 2 external components
Only 2 external components
Only 2 external components
PFM controller
PFM controller
PFM controller
Optimized for 1 cell input
Optimized for 2 cell input
Drives external MOSFEf
Optimized for 1 cell input
Drives external MOSFEf

Yes
Yes

C,E,M
C,E,M
C,E,M
C,E,M
C,E,M
C,E,M
C,E,M
C,E,M
C,E,M
C,E,M
C,E,M
C,E,M
C,E,M
C,E,M
C,E,M

1.74
2.88
2.56
2.56
2.56
2.87
2.87
2.87
3.35
3.35
3.35
3.35
3.35
3.20
2.66

0.200(0.090)
0.125(0.070)
0.4(0.135)
2.0(0.5)
2.5(0.75)
0.4(0.135)
2.0(0.5)
2.5(0.75)
(0.08)
(0.04)
(0.08)
(0.08)
(0.04)
4(2)
3(1.7)

200

PFM
PFM
PFM
PFM
PFM
PFM
PFM
PFM
PFM
PFM
PFM
PFM
PFM
PWM
PWM

Temp.

Yes
Yes
Yes

MAX733
MAX734
MAX741U

4to 11
1.9 to 12
1.8 to 15.5

15
12
5,12,15, adj.

3(1.7)
2.5(1.1)
3.5(1.6)

125
120
5W

PWM
PWM
PWM

DIP,SO
DIP,SO
DIP,SSOP

Yes
Yes
Yes

C,E,M
C,E,M
C,E,M

MAX751
MAX752
MAX7561757

1.2 to 5.25
1.8 to 16
1.1 to 5.S

5
Adj.
(3.3 or 5)/adj.

3.5(2)
4(2)
0.060

175
2.4W
300

PWM
PWM
PFM

DIP,SO
DIP,SO
DIP,SO

Yes
Yes
Yes

C,E,M
C,E,M
C,E

MAX761n62

2 to 16.5

0.1

120

PFM

DIP,SO

Yes

C,E,M

0.1

IA

PFM

DIP,SO

Yes

C,E,M

0.1

IA

PFM

DIP,SO

Hash memory programmer,
±4%, output voltage tolerance
Hash memory programmer
PWM step-up controller, 3VIN to
5VOUT at lA, 85% efficient
Best combination of low iQ & high
86% efficiency
12V flash programmer,
high efficiency over wide lOUT range
Controllers, high efficiency
over wide loUT range
Controller, high-voltage output,
high efficiency over wide lOUT range
On-chip active diode, true turn off in shutdown

MAX77on71n72

2 to 16.5

MAX773

3 to 16.5

12115 or adj.
to 16.5
5/12115 or
adj. to 28
Adj. to 48

MAX777n7sn79

lto6

51(3 or 3.3)1adj.

0.310(0.220)

300

PFM

DIP,SO

Yes

C,E,M

MAX856/857

1.1 to 5.5

(3.3 or 5)/adj.

0.060

150

PFM

DIP,SO

Yes

C,E

Best combination of low iQ & high
85% efficiency
Only 3 external components
>90% efficiencies over wide range
(lIoA to 225mA)
>90% efficiency over wide range, drives
external P-channel FET

C,E,M

3.23
2.23
3.64
2.35
3.20
1.95

tt
tt
tt
tt
tt

STEP-DOWN SWITCHING REGULATORS
MAX638
MAX63916401653

2.6 to 16.5
4 to 11.5

5,adj.
5/3.3/3 or adj.

0.6(0.135)
0.02(0.0\)

75
225

PFM
PFM

DIP,SO
DIP,SO

Yes

C,E,M
C,E,M

MAX64916511652

4 to 16.5

5/3.3/3 or adj.

0.100

lA

PFM

DIP,SO

Yes

C,E,M

=
=

tt

=

=

Package Options: DIP Dual-In-Line Package, SO Small Outline, SSOP Shrink Small-Outline Package
Temperature Ranges: C O°C to + 70°C, E -40°C to +85°C, M -55°C to +125°C
Prices provided are for design guidance and are FOB USA. International prices will differ due to local duties, taxes, and exchanges rates.
Future product - contact factory for pricing and aVailability.

=

=

2.56
2.96

tt

_ _ _ _ _ _ _ _ _ _ _ _ _ DCIDC Converters (continued)
(V)
_~)
DUAL'()UTPUT SWITCIDNG REGULATORS
±12,±15
MAX742
4.2 to 10
MAX743
4.2 to 6
±12,±15

Quiescent
Supply Current
(mA),
max(typ)

Output
(mA typ)

Control
Scheme

Package
Options·

EV Kit

Temp.
Ranges··

15(8)
30(20)

±15W
±1.5W

PWM
PWM

DIP,SO
DIP,SO

Yes

C,E,M
C,E,M

MAX753

4.5 to 6

3

to20W

PFM

DIP,SO

C,E

MAX754

4.5 to 6

3

to20W

PFM

DIP,SO

C,E

Part
Number

Part
Number

Inpul'
Voltage
Range

Input
Voltage
Range

00._

Output
Voltage

CCFTadj.,
-LCD adj.
CCFTadj.,
+LCDadj.

Quiescent
Supply Current
(mA),
rnax(typ)

Output
Voltage

..00

Output
(mA typ)

Package
Options·

20
100
100
±10

DIP,SO
DIP,SO
DIP,SO
DIP,SO
DIP
DIP,SO,TO-99
DIP,SO,TO-99
DIP,SO,TO-99

CHARGE-PUMP CONVEltTERS-UNREGULATED
MAXI044
1.5 to 10
-VIN' +2 x VIN
1.5 to 5.5
'VIN, +2 x VIN
MAX660
MAX665
1.5 to 8
-VIN, +2 x VIN
MAX680
2to6
±2xVIN
MAX681
2 to 6
±2 xVIN
ICL7660
1.5 to 10
-VIN, +2 x VIN
ICL7662
4.5 to 20
-VIN' +2 x VIN
Si7661
4.5 to 20
-VIN, + 2 x VIN

0.200(0.03)
1.0(0.6)
1.0(0.6)
2(1)
2(1)
0.175(0.110)
0.6(0.25)
2(0.3)

CHARGE·PUMP CONVERTERS·REGULATED
MAX619
2 to 3.6
5
MAX622
3.5 to 16.5
VIN+ 11V

0.15
0.5(0.07)

5oo!1A

DIP,SO
DIP,SO

MAX623

3.5 to 115.5

VIN+11V

0.5(0.07)

5oo!1A

DIP

MAX662

4.5 to 5.5

12

1(0.32)

30mA, guaranteed DIP,SO
over temp.

Input
Voltage
Range

Output
Voltage

Output
(mA typ
or min)

±1O
10
10
10

15mA

EV Kit

Yes

(V)

(V)

MODULES
MAX1732

4.5 to 6

12

1.7(0.07)

120

14 DIP

C

MAX1738

6.6 to 16

5

1.7(0.06)

500

14 DIP

C

MAX1743

4.5 to 5.5

±120r±15

20(2.2)

125 or 100

24 DIP

C

=

t
tt

=

=

C,E,M
C,E
C,E

Yes

Package
Options·

=

Temp.
Ranges·'

Package Options: DIP Dual-In-Line Package, SO Small Outline, SSOP Shrink Small-Outline Package, TO-_
Can
Temperature Ranges: C = DoC to +70°C, I = -25°C to+85°C, E= _40°C to +85°C, M = -55°C to+125°C
Prices provided are for design guidance and are FOB USA. International prices will differ due to local duties, taxes, and exchanges rates.
Future product - contact factory for pricing and availability.

Features

($)

Drives external MOSFETs
Internal power MOSFETs, production kit
available
CCFf backlight and -LCD outputs,
digital adjust
CCFf backlight and +LCD outputs,
digital adjust

3.91
4.49

Temp.
Ranges"
C,E,M
C,E,M
C,E,M
C,E,M
C,E
C,E,M
C,I
C,I

Quiescent
Supply Current
(rnA),
max(typ)

Part
Number

Pricet
1000-up

C

4.45
4.45

Pricet
1000-up

_ID

Features
60kHz osc. boost mode
8-pinSOIC

1.19
2.95
3.96
1.87

Dual output
No external components (internal caps)

4.64
1.09
1.86
1.86

tt

No inductors
3 external capacitors, high-side
switching MAX662
No external capacitors, high-side
switching
Flash memory programmer,
no inductors, lowest-cost

1.86
2.85
2.09

Price t
1000-up

Package Size
0.27" x 0.77" x 0.29"
(6.86 mm x 19.57mmx 7.37mm)
0.27" x 0.77" x 0.29"
(6.86 mm x 19.57mm x 7.37mm)
0.57" x 1.27" x 0.345"
(l4.42mm x 32.32mm x 8.75mm)

en

18.29
17.07

23.78

_ _ _ _ _ _ _ _ _ _ _ _ _ DCIDC Converters (continued)
Input
Voltage
Range

Output
Voltage

Part
Number

~

MAX724n24H
MAX726n26H
MAX727n27H
MAX728n28H
MAX729n29H
MAX730mOA
MAX738m8A
MAX741D

3.5 to 40/60
3.5 to 40/60
3.5 to 40/60
3.5 to 40/60
3.5 to 40/60
5.2 to 11
6 to 16
2.7 to 15.5

MAX744A
4.75 to 16
5
MAX746
4 to 15
5/adj.
MAX747
4 to 15
5/adj.
MAX748A
4.75 to 16
3.3
MAX750n50A
4 to 11
Adj.
MAX758n85A
4 to 16
Adj.
MAX763A
4 to 11
3.3
MAX787 n87H
3.5 to 40/60
5
3.3
MAX788n88H
3.5 to 40/60
MAX789n89H
3.5 to 40/60
3
LTl07411074HV
3.5 to 40/60
Adj.(2.5 to 40)
LTl07611076HV
3.5 to 40/60
Adj.L2.5 to 40)
INVERTING SWITCHING REGULATORS
MAX4391
4 to 16.5
up to -20
MAX634
2.3 to 16.5
up to -20
MAX635
2.3 to 16.5
-5, adj.
MAX636
2.3 to 16.5
-12, adj.
MAX637
2.3 to 16.5
-15, adj.
MAX650
-54 to -42
5
MAX735
4 to 6.2
-5
MAX736
4 to 8.6
-12
MAX737
4 to 5.5
-15
MAX739
4 to 15
-5
MAX741N
2.7 to 15.5
-5,-12,-15, adj.
MAX749
2 to 6
Adj.
MAX755
2.7 to 9
Adj.
MAX759
4 to 15
Adj.
MAX764n65n66
3 to 16.5
-51-121-15 or
adj. to 21VA
-51-121-15 or
3 to 16.5
MAX774n75n76
adj. to 21VA

t
tt

Quiescent
Supply Current
(rnA),

M~ax(typ}_

Output
(rnA typ)

Control
Scheme

Package
Options'

Adj.(2.5 to 40)
Adj.(2.5 to 40)
5
3.3
3
5
5
5, adj.

20(8.5)
20(8.5)
20(8.5)
20(8.5)
12(8.5)
3(1.7)
3(1.7)
4.0(2.8)

5A
2A
2A
2A
2A
300
750
3A

PWM
PWM
PWM
PWM
PWM
PWM
PWM
PWM

TO-220,TO-3
TO-220,TO-3
TO-220,TO-3
TO-220,TO-3
TO-220,T0-3
DIP,SO
Yes
DIP,SO
Yes
DIP,SSOP Yes

C,E,M
C,E,M
C,E,M
C,E,M
C,E,M
C,E,M
C,E,M
C,E,M

2.5 (1.2)
1
1
3(1.7)
3(1.7)
3(1.7)
3(1.7)
U(8.5)
12(8.5)
12(8.5)
20(8.5)

750
2.5A
2.5A
500
1.5W
3.75W
250
5A
5A
5A
5A

PWM
PWM
PWM
PWM
PWM
PWM
PWM
PWM
PWM
PWM
PWM
PWM

DIP,SO
Yes
DIP,SO
Yes
DIP,SO
Yes
DIP,SO
Yes
DIP,SO
Yes
DIP,SO
Yes
DIP,SO
Yes
TO-220,TO-3
TO-220,TO-3
TO-220,TO-3
TO-220,TO-3
TO-220,TO-3

~~____

~A_

0.25(0.09)
0.15(0.07)
0.15(0.08)
0.15(0.08)
0.15(0.07)
10(0.5)
3(1.6)
3(1.6)
4.5(2.5)
3(1.6)
4.0(2.2)
0.06
3.5(1.8)
4(2.1)
0.1

400mW
400mW
50
40
25
250
275
125
100
500
5W
5W
I.4W
1.5W
200

PFM
PFM
PFM
PFM
PFM
PFM
PWM
PWM
PWM
PWM
PWM
PFM
PWM
PWM
PFM

DIP,SO
DIP,SO
DIP,SO
DIP,SO
DIP,SO
DIP,SO
DIP,SO
DIP,SO
DIP,SO
DIP,SO
DIP,SSOP
DIP,SO
DIP,SO
DIP,SO
DIP,SO

0.1

lA

PFM

DIP,SO

EV Kit

Temp.
Ranges"

Pricet
1000-up
Features

($)

4.69
3.00
3.00
3.00
3.00
3.09
3.23
3.64

C,E,M
C,E,M
C,E,M
C,E,M
C,E,M
C,E,M
C,E,M
C,E,M
C,E,M
C,E,M
C,E,M
C,E,M

High power, few external components
High power, few external components
High power, few external components
High power, few external components
High power, few external components
90% efficiencies, MAX730A improves lOUT & dropout
>85% efficiencies, MAX738A improves lOUT & dropout
PWM step-down controller, 6.5VIN
to 5V OUT at 3A, 90% efficient
Optimized for cellular communications
90% efficiencies, drives external N-channel FET
90% efficiencies, drives external P-channel FET
>85% efficiencies
90% efficiencies, MAX750A improves lOUT & dropout
>85% efficiencies, MAX758A improves lOUT & dropout
80% efficiencies
High power, few external components
High power, few external components
High power, few external components
High power, few external components
High power, few external components

Yes
Yes

C,E,M
C,E,M
C,E,M
C,E,M
C,E,M
C,E,M
C,E,M
C,E,M
C,E,M
C,E,M
C,E,M
C,E,M
C,E,M
C,E,M
C,E,M

Improved RC4391 2nd source
Improved RC4391 2nd source
Only 3 external components
Only 3 external components
Only 3 external components
Telecom applications
>80% efficiencies
>80% efficiencies
>80% efficiencies
>80% efficiencies
PWM inverting controller, high efficiency
Digital adjust for - LCD
>80% efficiencies
LCD driver, >80% efficiencies
High efficiency over wide lOUT range

2.09
2.61
2.56
2.56
2.56
3.50
2.55
2.95
2.95
2.95
3.64
2.49
2.55
2.95

Yes

C,E,M

Controllers, high efficiency over wide

tt

Yes
Yes
Yes
Yes

Package Options: DIP = Dual-In-Line Package, SO = Small Outline, SSOP = Shrink Smail-Outline Package, TO-_ = Can
Temperature Ranges: C = O'C to +70'C, E= -40'C to +85'C, M= -55'C to +125'C
Prices provided are for design guidance and are FOB USA. International prices will differ due to local duties, taxes, and exchanges rates.
Future product - contact factory for pricing and availability.

loUT range

tt
tt

tt
tt
2.92
3.23

tt
4.69
4.69
4.69
4.83
3.03

tt

________________ Linear Voltage Regulators
M

Quiescent
Current
(IlA).
max(typ)

('Yo)

N/A
N/A
N/A

150(70)
150(70)
150(70)

MAX663
2 to 16.5
Fixed 5 or adj.(1.3 to 15)
MAX666
2 to 16.5
Fixed 5 or adj.(1.3 to 15)
MAX667
3.5 to 16.5
Fixed 5 or adj.(1.3 to 15)
MAX682-685
2.7 to 12
Adj.l5/3.313
ICL7663
1.5 to 16
Adj.(1.3 to 15)
ICL7663A
2.0 to 16
Adj.(1.3 to 15)
ICL7663B
1.5 to 16
Adj.(1.3 to 15~
DC LINEAR REGULATORS-NEGATIVE OUTPUT

0.9 at40mA
0.9 at40mA
0.15 at200mA
0.1 at200mA
0.9at4OmA
0.9 at40mA
0.9 at40mA

12(6)
12(6)
25(20)
15(5)
10(3.5)
10(3.5)

MAX664
ICL7664
ICL7664A

0.35 at40mA
0.4 at30mA
0.4 at30mA

Part
Number

Input
Voltage
Range

M

Output
Voltage

rtL____ ___

AC-DC REGULATORS
1201240VAC
Fixed 5 or adj.(1.3 to 9)
MAX610
MAX611
120l24OVAC
Fixed 5
MAX612
1201240VAC
Fixed 5 oradj.(1.3 to 15)
DC UNEAR REGULATORS-POSITIVE OUTPUT

t!

-2 to -16.5
-2to-16
-2to-16

Fixed -5 or -1.3 to -15
-1.3 to-IS
-1.3 to -15

Dropout
Voltage

Output
Voltage
Accuracy
Shutdown

Package
Options'

Temp.
Ranges"

Pricet
1000-up
($)

±4
±4
±4

No
No
No

DIP
DIP
DIP

C
C
C

1.30
1.30
1.30

±5

Yes
Yes
Yes
Yes
Yes
Yes
Yes

DIP,SO
DIP,SO
DIP,SO
DIP,SO
DIP,SO,TO-99
DIP,SO,TO-99
DIP,SO,T0-99

C,E,M
C,E,M
C,E,M
C,E,M
C,E,I,M
C,E,I,M
C,E,I,M

1.91
2.22
2.35

1O(3.5~

±5
±4
±4
±8
±1
±8

12(6)
10(3.5)
10(3.5)

±5
±8
±l

Yes
Yes
Yes

DIP,SO
DIP,SO,TO-99
DIP,SO,TO-99

C,E,M
C,I,M
C,I,M

2.33
1.27
1.56

Package Options: DIP = Dual-In-Line Package, SO = Small Outline, TO- _= Can
Temperature Ranges: C = O°C to +70°C, I = _25°C to +85°C, E = _40°C to +85°C, M = -55°C to + 125°C
Prices provided are for design guidance and are FOB USA. International prices will differ due to local duties, taxes, and exchange rates.
Future product - contact factory for pricing and availability.

tt
1.81
1.99
1.81

_______________________________ Dmpmy Power Supplies
Input Voltage
Range

DC-DC Output
Voltages

Part
Number

('tL

M

MAX149
MAX153

2 to6
6 to 24

Negative LCD
CCFf drive, configurable;
Negative LCD, configurable
CCFr drive, configurable;
Positive LCD, configurable
Negative LCD, adiustable

MAX154

6 to 24

MAX759

4to 15

Qulscent Supply
Current
(jtA typ)

EV Kit

60
100

Yes

100
1.2mA

Yes

Pricet
1000-up

Package
Options·

Features

($)

DIP/sO
DIP/sO

Digital LCD adjustment
Digital CCFr and LCD adjustment

2.49
4.45

DIP/sO

Digital CCFr and LCD adjustment

4.45

DIP/sO

Internal MOSFET

2.95

_______________________ PCMCIA / Flash Memory Supplies
Part
Number
MAX662
MAX717-721

MAX132
MAX134
MAX161

MAX180
MAX1732

Pricet

Input Voltage
Range
M

12V Output
Current
(mA)

EV Kit

Package
Options·

4.5 to 5.5
0.9 to 5.5
(battery),7 to 18
(plug-in adapter)
4.0 to 9.3
1.9 to 11
2 to 165

30
120

Yes
Yes

DIP/SO
SO

200
120
120

Yes
Yes
Yes

DIP/sO
DIP/sO
DIP/sO

3.3/5/12
4to6

Two Vpp outputs, 60mA each
120

1~up

DIP/sO
DIP

Features

($)

No inductors, low cost
Built-in switchover from main battery to plug-in
adapter power, low-voltage warDing, AC detect, clock
& RAM keep-alive mini-switcher from backup battery
4% output tolerance
Small8-pin package, adjustable soft-start
12V flash programmer,
high efficiency over wide lOUT range
Industry-standard interface, Vpp outputs,VCC control
Module, no external-components

2.09

4.95

2.66
2.23

tt
2.25
18.29

~__----------------------------------BatteryChargers
Charge
Termination

Part
Number

No. of Cells
Charged

Fast-Charge

Trickle-Charge
Rates

Method

MAX112

1 to 16 NiMH

CI3 to4C

Cl16, adj.

!J.V/I1t;=(J,
Temp., Tuner

MAX113

1 to 16 NiMH
orNiCd

Cl3to4C

Cl16, adj.

!J.V!!J.t900/0 Efficiency
80% to 95% Efficiency for Loads from 5mA to Full-Load
The MAX782, MAX783 , and MAX786 controller ICs incorporate a 3.3V supply, a 5V supply, and
two precision comparators for voltage monitoring-all in a single shrink small-outline package (SSOP).
The MAX782/MAX783 also include dual PCMCIA analog-control outputs and a third comparator. All
devices accept inputs from NiCd or NiMH battery stacks of 6 to 14 cells (5.5V to 30V).
The MAX782/MAX783/MAX786 use synchronous rectification with low-cost, N-channel MOSFET
switches to achieve 90% efficiency over a wide range of loads. Even at 5mA, efficiency is 80%. Only
70llA quiescent current is needed in standby mode, extending battery life in both suspend and run
modes. Each output is configurable for loads from 5W to 50W, and each can be shut down independently.
Fixed-frequency PWM control allows easy
filtering for wireless systems and helps preSYSTEM BLOCK DIAGRAM
vent interference in pen-based computers.
INPUT
5.5T030Y
Filtering requires only 30llF of output capaciMAXIM
MAXl82
tance per ampere of load-far less than that
MAXl83
required by conventional PWM controllers.
MAX186
The MAX782/MAX783 support dual
(6 TO 12 CELL
.,.*,
PCMCIA slots with integral VPP outputs and
three high-side drivers for Vee control. VPP
control is compatible with industry-standard
OV/5V/12V'
digital PCMCIA controllers. VPP outputs are
3.3VENABLE
programmable to 12V, 5V, OV, or bigh-Z. The
(60mA)
5VENABLE
MAX783 is optimized for six-cell operation.
OV V/12V'
OSCILLATOR
SYNC
The MAX786 is configured for applications
(60mA)
vpp CONTROL
that do not require PCMCIA compatibility.
Complete, surface-mount evaluation kits are
'MAX782 AND MAX783 DNl Y
available for the MAX782 and MAX786.

ft

II

The MAX7821MAX7831MAX786 deliver 3.3V and 5V outputs, power dual
PCMCIA card slots, and operate from S.SV to 30V inputs.

3.3V- or 5V-Output Step-Downs Are
91°A» Efficient for Load Currents
Ranging from lmA to 225mA
Compact Switcher Draws Only lOJ..lA Quiescent Current
The MAX639 /MAX640 /MAX6S3 switching
regulators extend battery life by providing
> 90% EFFICIENCY FOR 1mA TO 22SmA LOADS
ultra high-efficiency step-down regulation,
especially in applications with dynamic loadEFFICIENCY vs. OUTPUT CURRENT
100 r-----,------,,------,-----,
current requirements. Efficiency with SVout~
puts is greater than 90% for output currents
~ 95~--~~~===+.=7.~~~--~
from lmA to 22SmA-a dynamic range exceed~
I
~ 90~_T~~~----~~~~~~~-~
ing two orders of magnitude! The regulators'
It
a:
unique "constant peak current" design draws
~ 85bL~~~~----~------~------~
only I O~A of quiescent current and allows the
80L-~_~~_ _~_ _ _~~~~UT~=_5V_~
use of external components that are smaller
1001lA
lmA
lOrnA
lA
100mA
than those in typical switch-mode converters.
OUTPUT CURRENT
These step-down converters save space,
requirirlg only four external components and
fitting in 0.Sin2 . The MAX639 has a preset SV The MAX639 exhibits> 90% efficiency over loads that vary by two
±4% output. The MAX640 and MAX6S3 have orders of magnitude.
preset 3.3V and 3.0V outputs, respectively. Outputs can also be adjusted from 1.3V to VIN'
Maximum input voltage is 11.SV. Complete surface-mount or through-hole evaluation kits are available.

3.3V DC-DC Converters Deliver 2.5A
with 85°A» to 95°A» Efficiency
Build a Complete 2.5A Converter in < O.9in2
The MAX746 and MAX747 are fixed-frequency
PWM controllers for low-noise step-down applica3.3V at 2.SA OUTPUT WITH >85% EFFICIENCY
tions requiring up to 2.SA of output current. They
INPUT - - , - - - - - - - - ,
have 8S% to 9S% efficiency over a wide load range
4.75V
(SOmA to 2.SA), thanks to a dual-mode control
T015V
scheme that minimizes Switching losses by reducing Switching frequency at light loads. The devices
ONiOff
maximize battery life whether your system is running at full power or is in standby mode.
Quiescent supply current is lmA, or only 20~A in
shutdown (both max over temperature). The controllers include a precision low-battery detector,
soft-start, and cycle-by-cycle current limiting.
The MAX746 is configured to drive an external,
N-channel power MOSFET on the high side, whereas Save battery life and board space with the MAX7461MAX747.
the MAX747 is configured to drive P-channel power They fit into < 0.9in2 and have 85% to 95% efficiency.
MOSFETs. The MAX746 comes in 16-pin DIP and
narrow SO packages; the MAX747 comes in 14-pin DIP and narrow SO packages. And to save valuable
time, a surface-mount evaluation kit is available.

Step-Down Switching Regulators
Have 5A or 2A Internal Switch
Save Space: Few External Components Needed
The MAX724 and MAX787/MAX788/MAX789 5A, switch-mode, step-down DC-DC regulators feature
a wide 8V to 40V input range (to 60V for the high-voltage "H" versions). The MAX726-MAX729 output 2A
All of these devices require few external components, since the power switch, oscillator, and control circuitry are on chip.
Though optimized for step-down applications,
these versatile regulators can also be
configured as inverters, negative boost converters,
or flyback converters, with input voltages as low as
5V. Fixed outputs are 5V (MAX727/MAX787),
3.3V (MAX728/MAX788), and 3V (MAX729/
MAX789); the MAX724 and MAX726 are adjustable
from 2.5V to 40V (to 60V for the "H" version). All
devices have a preset 100kHz internal oscillator,
which can also be adjusted to 200kHz in the
MAX724 and MAX726. Cycle-by-cycle current limiting protects against overcurrent faults and shortcircuit output faults. Quiescent current is 8.5mA.
These easy-to-use pulse-width-modulating
2A STEp· DOWN CONVERTER
(PWM) switching regulators are available in 5-pin
TO-220, 7-pin TO-220, and 4-pin TO-3 packages.
The MAX727 outputs 2A at a fixed 5V output, while requiring only 6
external components.

Step Down to 5V or 3.3V Outputs
with 90% Efficiency & Low Noise
Small PWM DC-DCs Deliver Guaranteed 750mA, Require No Design
The MAX730/MAX738 fixed 5V-output,
MAX763A/MAX748A fixed 3.3V-output, and MAX750/
MAX758 adjustable-output (from 1.25V up to VIN) stepdown converters extend battery life and save space in
portable applications. They provide high-efficiency
(85% to 95%) step-down regulation and fit into less
than O.5in 2 of board space. Quiescent current is
1.7mA in normal operation and 6JlA in lOgic-controlled
shutdown. Preselected component values (including
only one l00JlH inductor value for all applications) and
evaluation kits greatly simplify design work and component gathering.
The MAX730, MAX763A, and MAX750 are guaranThis MAX730 step-down circuit can deliver up to 1A at 5V and
teed
over temperature to deliver 300mA at 3.3V or 5V
fits In 0.5In 2•
for inputs up to llV. The MAX738 , MAX748A, and
MAX758 deliver 750mA at 3.3V or 5V, guaranteed for
inputs up to 16V. All devices are capable of supplying up to lA The output of the MAX750 and the
MAX758 is set using a resistor dMder.
High-frequency 160kHz pulse-width-modulation (PWM) current-mode control provides easy-to-filter,
fixed-frequency output ripple, allowing use in cellular phone applications.

Dual-Output Palmtop Power SuppHes
Step Up from 1.8V Batteries
Power IlP and Program Flash Memories with 87% Efficiency
The MAX717-MAX721 dual-output switching regulators provide an unbeatable combination of high
efficiency (870Al), low supply current (60I1A quiescent, 20l1A in shutdown), and small size (I6-pin narrow
SO package). They fit perfectly in palmtop and other battery-powered microprocessor applications, and
start up from inputs as low as l.8V, guaranteed
over temp. And they continue to operate for inputs
DUAL-oUTPUT REGULATOR
down to 0.9V. Integrated features include low outPOWERS liP & PROGRAMS FLASH MEMORY
put voltage warning, automatic switchover between
OUTPUTS
battexy power and wall-adapter power, logic-signalINPUTS
ing when wall adapter is in use, and a mini backup
switcher powered by the backup battexy to keep
alive memoxy and clock. Outputs are logic controlled. An evaluation kit for the MAX718 is available.
Part

Main
Output
(V)

MAX717
MAX718
MAX719
MAX720
MAX721

Backup
WalIAdapter KeepOutput Detect
Alive
SiIDlal Switcher
Aux.

3.3
3.3 or 5
3.0 or 5
3.3 or 5

FlASH

YES

YES

FlASH
FlASH

NO
NO

YES

FlASH

YES

3.0 or 5

FLASH

YES

Total
Shutdown

YES

NO
NO

BACKUP BAffiRY

NO
NO
NO
YES

The MAX718 generates both 3.3VI5V AND 5VI12V output. from battery inputa down to O.9V, and it atarts up from Inpula a.low a.
1.8V, guaranteed.

YES

Single IC Powers JlP and
Negative-Voltage LCD from 1.8V
The MAX722 and MAx723 feature the same small
size, high efficiency, and low supply current as the
MAX717-MAX72l. They step up from l.8V batteries to
power 3V and 5V microprocessors, and also invert down
to -40V for LCDs. Their high Switching frequency (up to
500kHz) allows the use of tiny surface-mount magnetics
(2211H, <5mm diameter). Supply current is a low 6OI1A
due to CMOS construction and a unique constant-offtime pulse-frequency-modulation (PFM) control scheme.
Efficiency is 87% (10% better than low-voltage bipolar
regulators). An evaluation kit is available for the
MAX722.

Part

Main
Output

MAX722
MAX723

3.3 or 5
3.0 or 5

(V)

WalI- Backup
Adapter KeepOutput Detect Alive
Signal Switcher
Aux.

LCD
LCD

NO
NO

NO
NO

DUAL-OUTPUT REGULATOR
POWERS liP & NEGATIVE LCD

Total
Shutdown
YES
YES

MAX722 and MAX723 Integrated features include low-voltage warning and automatic switching between battery
power and wall-adapter power.

Program 12V Flash Memories
Without Inductors!
World's Lowest Cost and Smallest Solution Fits in Only O.2in2
FLASH MEMORY PROGRAMMER
O.11JF

INPUT
4.75 TO 5.25V

::r:+4.7~F

I--_ _-~WUT
30mA

ON/OFF _ - - - - I
O.22~F

O.221JF

The MAX662 is the world's first charge-pump
flash memory programming supply. It uses only
low-cost capacitors to provide a regulated 12V ±S%
output. Output current is guaranteed to be 30mA
over the commercial temperature range (O°C to
+70°C) for inputs from 4.7SV to S.SV.
While operating. quiescent supply current is
320j.l.A. In shutdown mode. the output drops to
SV and the quiescent current drops to 7 OJ.l. A.
Programming control is directly enabled via the
lOgic-controlled shutdown pin.
This compact and low-cost solution requires
only a handful of capacitors that total about 3S¢
and. along with the MAX662. fit into about 0.2in2
of board space. The MAX662 evaluation kit is
available to speed design cycles.

This entire MAX662 circuit, Including external components, cost less
than $2.10 (10,000 pc. pricing) and fits In less than 0.2In2.

Guaranteed 120mA, 12V-Output
Flash Memory Supply Fits in O.3in 2
8-Pin SOIC is 880/0 Efficient, Steps Up from 4.75V
The MAX734 delivers 120mA at 12V ±S%.
guaranteed over temperature. from inputs as
FLASH MEMORY PROGRAMMER
low as 4.7SV. It saves space and battery life
GUARANTEES 12V AT 120mA OUTPUT
in palmtop and notebook computers and
other systems using flash memory.
INPUT
2V_ _-T-_ _tT-l
4.75VTO=--1eAlso. the MAX734 can be configured in a
OUTPUT
bootstrapped application that delivers 12V at
12V ±5% r - - - - . ,
120mA
120mA from inputs down to 1.9V. Typical
---+--~----oJ Vpp
effiCiency for that application is SO%.
Available in S-pin SO and DIP packages.
FlASH
MEMORY
it uses only a diode. an ISj.l.H inductor, and
two 33j.1.F capacitors. The entire circuit is
completely surface-mountable and fits into
less than 0.3in2 .
Battery-saving features include 88% efficiency. 1.2mA quiescent supply current.
70j.l.A shutdown supply current. and controllable The MAX734 Is an s·pln so that steps up from a 4.75V input to a 12V
soft-start to reduce surge currents at start-up. output at 120mA and fits into < 0.3 in2.
Shutdown and programming control can be easily and directly interfaced with a microprocessor
using the lOgic-controlled shutdown pin.
The MAX734 is an S-pin SO version of the popular MAX732 flash memory programming supply.
The MAX732 comes in a 16-pin wide SO package and delivers a guaranteed ISOmA from a 4.SV
input. Evaluation kits for both the MAX734 and the MAX732 are available.

Palmtop, Cell Phone, Disk Drive
Power Supply Starts Up from 1.8V
Surface-Mount Ie Draws Only 1.6mA, Delivers 5Vat IA
The MAX741U's unique pairing oflow start-up voltage
(as low as 1.8V) and low 1.6mA quiescent current (50IlA in
shutdown) makes it the best choice for battery-operated and
portable power-supply designs that require high currents
from low input voltages. Efficiency is typically above 85%.
Its pulse-width-modulated (PWM) control scheme keeps
output ripple at an easy-to-filter fixed frequency, making the
MAX741U particularly well suited for cellular phone and
radio designs. Other applications include stepping up to 5V
at lA to power disk drives in 3V-only systems, and delivering 5V at 500mA from 3V battexy inputs in palmtop computers.
The device integrates many useful pin-programmable
features, such as an external oscillator sync pin, which
allows the output ripple frequency to be adjusted outside
the transmission band for cellular phone applications.
Other features include preset 5V, 12V, 15V, or adjustable
±4% outputs.
The MAX741 U evaluation kit demonstrates a typical
2.7V input/5V at lA output step-up application and shows
off the tiny 20-pin SSOP package.

POWER 5VI1A TRANSMITTERS IN
3V PHONES WITH 80% EFFICIENCY

2J~PTW5=Vt----.--------,
2o,.H

OUTPUT
5V@lA

0.10

r

The MAX741 U steps up to 5V at lA from inputs as low as
2.7V. It features 1.6mA quiescent current and a tiny 20-pin
SSOP package. (This simplified drawing shows only major
components.)

Linear Regulator Powers 200mA
Load with 150mV Dropout
& 5mA Supply Current
Best Combination of Low Supply Current and Low Dropout
QUIESCENT CURRENT vs. LOAD CURRENT
~

20

ig;

15

a

!Z

I

~

5

a

0

~

I

LINEAR
10 ~~POLAR
EGULATOR ~

0.1

..,.,

./

MAX667

10
100
LOAD CURRENT (mA)

DROPOUT VOLTAGE vs. LOAD CURRENT
>' 400

I

.§.

~ 300

;0

g

200 -{lPOLAR LINEAR

~

100

~

I
MAX667

EGULATOR~

0

0.1

../
..-"
10

....

100

The MAX667 outperforms typical bipolar linear regulators with its unique combination of low supply current and low Input/output ·.oltage differential.

The MAX667 low-dropout linear regulator offers an
unbeatable combination of low dropout voltage and low quiescent current for prolonging useful battery life in portable
applications. In addition, it also has O.2IlA shutdown supply current for saving the battexy when the system is not in
use. It delivers 200mA at 5V with an input as low as
5.15V-a useful capability in 5V systems powered by 5-cell
NiCd or 3-cell lead-acid batteries. Short-circuit protection
prevents output currents greater than 450mA.
In normal mode, the MAX667's no-load supply current
is 201lA. For 200mA loads, the device consumes just 5mA.
The output is preset to 5V ±4%. guaranteed over temperature, but it can be adjusted from 1.3V to 16V with two resistors. The MAX667 requires only a 10IlF output capacitor.
The regulator features an on-chip low-battery input/output
comparator and a "dropout" indicator that signals when the
PNP pass transistor is about to saturate.

Flash Programming & DC-DC
Converter Modules Use 6x Less
Space than Comparable Modules
No External Components or Design Work Needed
The MAX1732 flash memory programming supply and
MAX1738 step-down DC-DC converter fit in miniature 14-pin DIP
STEP DOWN
modules measuring just 0.27" long x 0.77" wide x 0.29" high
TO+5V
(6.86mm x 19.57mm x 7. 37mm). using only 0.25in2 (1.6cm2) of
board space. No external components or design work are
required. since all components are contained in a single module.
The MAX1732 programs 12V. 120mA flash memories: 120mA
output current and ±4% output voltage regulation are guaranteed
over temperature for inputs from 4.5V to 6V. The MAX1738 per14-Pin DIP Only 0.29" High
forms 5V. 500mA step-down conversions. and accuracy is guaran0.27" x 0.77" x 0.29"
(6.86mm x 19.57mm x 7.37mm)
teed over all specified conditions of line. load. and temperature.
Typical efficiencies exceed 85%· (MAX1732) or 86% (MAX1738).
No-load supply current is 1. 7mA for both devices. and reduces to
just 70~A (MAX1732) or 6O~A (MAX1738) in lOgic-controlled shutdown mode.
The MAX1743 is a complete DC-DC module that converts a
+5V input to a dual ±12V or ±15V output: It supplies 125mA at
±12V. or l00mA at ±15V. Positive and negative outputs are independently regulated to within ±4% over all specified conditions of
line. load. and temperature. This 24-pin DIP module measures 0.57" long x 1.27" wide x 0.345" high.
Typical efficiencies are 82%. On-board cycle-by-cycle current sensing. soft-start. and undervoltage
lockout ensure reliable operation.

Appendix G
Future Products

.AIIAXUM _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

111

* FUTURE PRODUCTS*

lOOmA Step-Up Converters Have
850/0 Efficiency, 150J.1A IQ'
and 20J.1A Shutdown
The MAX856 and MAX857 step-up DC-DC converters feature low quiescent currents and high efficiencies. From 2V inputs, the MAX856 delivers 100mA at 5V or 150mA at 3.3V. The output voltage is
pin-selectable. The MAX857 has an adjustable output from 2.7V to 5.5V. The MAX856/MAX857 are
designed for applications requiring small size and long battery life. These pulse-skipping converters
have a 400mA switch current limit, which permits the use of very inexpensive and extremely small surface-mount inductors. Minimum start-up voltage is guaranteed to be 1.8V, and the devices will remain
operating with inputs down to 1.1V. Both devices are available in 8-pin DIP and SO packages. A complete, surface-mount evaluation kit is available. (Release Date: September 1993)

Step-Up, Step-Down & Inverting
Battery-Powered DC-DC Converters
Have High Efficiency, Low IQ' 8-Pins
Maxim's new family of step-up, step-down, and inverting DC-DC converters lengthen battery life.
These compact and easy-to-use converters feature quiescent currents under 100J.lA, shutdown currents under 5J.lA, and efficiencies of 800Al to 95%. Efficiency stays constant, even over loads ranging
from lmA to lA, thanks to a unique current-limited pulse-skipping control scheme. Minimal component count and 300kHz switching frequencies keep external circuitry small, saving space. All devices
are available with internal power switches or as controllers using external power switches. Outputs
are preset or adjustable. Preassembled surface-mount evaluation kits and free samples will be available to speed designs. Refer to the product tables at the end of the Design Guide for specific information. (Release Date: October 1993)
MAX639*/MAX640/MAX653
MAX649/MAX651/MAX652
MAX756/MAX757
MAX761/MAX762
MAX770-MAX773
MAX764/MAX765/MAX766
MAX774/MAX775/MAX776

• AvaUable rww

5V/3.3V/3V, Step-Down DC-DC Converters
5V/3.3V/3V, Step-Down DC-DC Controllers
(p-Channel External Switch)
3.3Vor 5V/ Adjustable, Step-Up DC-DC Converters
12V/15V, Step-Up DC-DC Converters
5V/ 12V/ 15V/ Adjustable, Step-Up DC-DC Controllers
(N-Channel External Switch)
-5V/-12V/-15V, Inverting DC-DC Converters
-5V/-12V/-15V, Inverting DC-DC Controllers
(p-Channel External Switch)

* FUTURE PRODUCTS *
IV-Input DC-DC Converters
Step Up to 5V or 3.3V at IOOmA
The new MAX777, MAX778 , and MAX779 DC-DC converters step up IV to 6V inputs to outputs
of 3V, 3.3V, or 5V (or are adjustable from 2.7V to 6Vl. They require only two external components (a
lOOJ.1F output capacitor and a 22J.1H inductor) to deliver over IOOmA from IV inputs. From 2V inputs,
they deliver up to 240mA, guaranteed over temp. An on-chip synchronous rectifier takes the place of
the external catch diode, and permits true shutdown by placing a high resistance in the DC path from
the input to the output.
Battery life is lengthened due to 85% typical efficiencies and a 31OJ.1A (max over temp.) quiescent
supply current, which is further reduced to 30J.1A in shutdown. A complete, preassembled surfacemount evaluation kit is available. (Release Date: September 1993)

DC-DC Converter Gives Constant
3.3V or 5V Output from I V to 6V
Input, without a Transformer
The new MAX877, MAX878 , and MAX879 step-up/step-down DC-DC converters provide a regulated output from input voltages above, below, and equal to the output. They come in 8-pin DIP and
SO packages, and require only an input capacitor, output capacitor, and 22J.1H inductor. They have a
IV to 6V input range and deliver up to 300mA. An on-chip synchronous rectifier takes the place of
the external catch diode, and permits true shutdown by placing a high resistance in the DC path from
the input to the output.
Battery life is lengthened due to 85% typical efficiencies and a 31OJ.1A (max over temp.) qUiescent
supply current, which is further reduced to 30J.1A in shutdown. Typical applications include 3.3V or
3V outputs from one lithium battery or two or three NiCd batteries, and delivering 5V from four alkaline cells. The MAX877 has a 5V output, the MAX878 has a pin-selectable 3V or 3.3V output, and the
MAX879 has an adjustable 2.7V to 6V output. An evaluation kit is available. (Release Date: October
1993)

* FUTURE PRODUCTS *
200mA Linear Regulators Have UltraLow 5J..LA Quiescent Current and Low,
lOOmV Dropout Voltage
at 200mA Outputs
The new MAX682-MAX685 family of linear regulators features a P-channel MOSFET pass transistor. which reduces quiescent supply currents to just 51lA And. because there are no base currents
like those found in conventional PNP bipolar linear regulators. the supply current stays low. independent of output current. In shutdown. the supply current drops even more-to less than lilA (max over
temp.). The low dropout voltage further ensures maximum battery life.
.
The input supply range is 2.7V to 12V. Output accuracies are ±4% over line. load. and temperature. The MAX682 has an adjustable output from 2.7V to VIN and an LBI/LBO low-battery detector.
The MAX683. MAX684. and MAX685 have 5V. 3.3V. and 3V outputs. respectively. They have two
LBI/LBO low-battery detectors. All devices come in 8-pin DIP and SO packages. and require only
O.331lF of output capaCitance. (Release Date: September 1993)

Charge Pump Delivers 5V from 2V
Needs No Inductors
The new MAX619 charge-pump voltage converter delivers 15mA (guaranteed over temp.) at 5V
from one lithium battery cell or two NiCd or alkaline battery cells (2V to 3.6V). without uSing inductors.
It comes in 8-pin DIP and SO packages. and uses only two in~enSive O.221lF capacitors and a 10IlF
output capacitor. The device fits in less than O.33in2 (2.1cm ). and is ideal for generating 5V logic
supplies and analog biases in portable. battery-powered instruments.
Quiescent current is only 150llA (max over temp.) when operating. and less than IOIlA in shutdown.
The output is regulated to 5V ±4% over line. load. and temperature. (Release Date: January 1994)
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