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19-2239; Rev 2; 3/09

KIT
ATION
EVALU
E
L
B
AVAILA

500kHz, 36V Output, SOT23,
PWM Step-Up DC-DC Converters

The MAX5025–MAX5028 constant-frequency, pulsewidth modulating (PWM), low-noise boost converters
are intended for low-voltage systems that often need a
locally generated high voltage. These devices are
capable of generating low-noise, high output voltages
required for varactor diode biasing in TV tuners, set-top
boxes, and PCI cable modems. The MAX5025–
MAX5028 operate from as low as 3V and switch at
500kHz.
The constant-frequency, current-mode PWM architecture provides for low output noise that is easy to filter. A
40V lateral DMOS device is used as the internal power
switch, making the devices ideal for boost converters
up to 36V. The MAX5025/MAX5026 adjustable versions
require the use of external feedback resistors to set the
output voltage. The MAX5027/MAX5028 offer a fixed
30V output. These devices are available in a small, 6pin SOT23 package.

Applications

Features
♦ Input Voltage Range:
3V to 11V (MAX5026/MAX5028)
4.5V to 11V (MAX5025/MAX5027)
♦ Wide Output Voltage Range: VCC to 36V
♦ Output Power: 120mW (max)
♦ User-Adjustable Output Voltage with
MAX5025/MAX5026 Using External Feedback
Resistors
♦ Fixed 30V Output Voltage: MAX5027/MAX5028
♦ Internal 1.3Ω (typ), 40V Switch
♦ Constant PWM Frequency Provides Easy Filtering
in Low-Noise Applications
♦ 500kHz (typ) Switching Frequency
♦ 1μA (max) Shutdown Current
♦ Small, 6-Pin SOT23 Package

TV Tuner Power Supply
Low-Noise Varactor Diode Biasing

Ordering Information

Set-Top Box Tuner Power Supply

PART

PCI Cable Modem
Voice-Over-Cable

TEMP RANGE

PIN-PACKAGE

MAX5025EUT-T

-40°C to +85°C

6 SOT23-6

MAX5026EUT-T

-40°C to +85°C

6 SOT23-6

LCD Power Supply

MAX5027EUT-T

-40°C to +85°C

6 SOT23-6

Avalanche Photodiode Biasing

MAX5028EUT-T

-40°C to +85°C

6 SOT23-6

Typical Operating Circuit
Selector Guide appears at end of data sheet.
VCC = 4.5V TO 11V
(MAX5027)
VCC = 3V TO 11V
(MAX5028)

L1
D1
LX

VCC

TOP VIEW

MAX5027
MAX5028
SHDN
FB
C1

Pin Configuration

VOUT
30V

C2

PGND 1

PGND
GND 2

MAX5025–
MAX5028

6

LX

5

VCC

4

SHDN

GND
FB 3

SOT23-6

________________________________________________________________ Maxim Integrated Products

1

For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.

MAX5025–MAX5028

General Description

MAX5025–MAX5028

500kHz, 36V Output, SOT23,
Step-Up DC-DC Converters
ABSOLUTE MAXIMUM RATINGS
VCC to GND ............................................................-0.3V to +12V
PGND to GND .......................................................-0.1V to +0.1V
FB to GND (MAX5025/MAX5026)...............-0.3V to (VCC + 0.3V)
FB to GND (MAX5027/MAX5028)...........................-0.3V to +40V
SHDN to GND.............................................-0.3V to (VCC + 0.3V)
LX to GND ..............................................................-0.3V to +45V
Peak LX Current ................................................................600mA

Operating Temperature Range ...........................-40°C to +85°C
Continuous Power Dissipation (TA = +70°C)
6-Pin SOT23 (derate 8.7mW/°C above +70°C)..........695.7mW
Junction Temperature ......................................................+150°C
Storage Temperature Range .............................-65°C to +165°C
Lead Temperature (soldering 10s) ..................................+300°C

Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.

ELECTRICAL CHARACTERISTICS
(VCC = 5V, SHDN = VCC, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 1)
PARAMETER

SYMBOL

CONDITIONS

MIN

TYP

MAX

UNITS

SUPPLY VOLTAGE
Input Voltage Range
Undervoltage Lockout
Supply Current
Shutdown Current

VCC
VUVLO
ICC
ISHDN

MAX5026/MAX5028

3.0

11

MAX5025/MAX5027

4.5

11

Rise/fall, hysteresis = 3mV

2.25

V

2.65

2.95

V

MAX5025/MAX5026, FB = 1.4V
MAX5027/MAX5028, FB = 35V

350

1000

µA

SHDN = GND

0.01

1

µA

BOOST CONVERTER
Switching Frequency

fSW

MAX5025/MAX5027

345

500

1000

MAX5026/MAX5028, VCC = 3.3V

410

500

670

MAX5025/MAX5027,
ILOAD = 2mA, VCC = 4.5V to 11V,
VOUT = 30V

0.25

Line Regulation

%/V
MAX5026/MAX5028,
ILOAD = 0.5mA, VCC = 3V to 11V,
VOUT = 30V

0.25

MAX5025/MAX5027,
VCC = 5V, ILOAD = 0 to 4mA,
VOUT = 30V

2.0
%

Load Regulation
MAX5026/MAX5028,
VCC = 3.3V, ILOAD = 0 to 1mA,
VOUT = 30V
Thermal Shutdown
Thermal Shutdown Hysteresis

2

kHz

1.0
140

°C

2

°C

_______________________________________________________________________________________

500kHz, 36V Output, SOT23,
Step-Up DC-DC Converters
MAX5025–MAX5028

ELECTRICAL CHARACTERISTICS (continued)
(VCC = 5V, SHDN = VCC, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 1)
PARAMETER

FB Set Point

SYMBOL

VFB

FB Input Bias Current

IFB

Output Voltage
Adjustment Range

CONDITIONS

MIN

TYP

MAX

MAX5025, VCC = 4.5V to 11V

1.19

1.25

1.31

MAX5027, VCC = 4.5V to 11V

28.5

30.0

31.5

MAX5026, VCC = 3.3V to 11V

1.212

1.25

1.288

MAX5028, VCC = 3.3V to 11V

29.0

UNITS

V

30

31

MAX5025/MAX5026, FB = 1V

110

310

nA

MAX5027/MAX5028, FB = 30V

100

170

µA

36

V

VCC + 1

MAX5025/MAX5026

LX OUTPUT

LX On-Resistance

RON

ILX = 40mA

Switch Current Limit

ILIM

Note 2

MAX5026/MAX5028,
VCC = 3V

2.0

4.0

VCC = 5V

1.3

3.0

1.0

2.5

VCC = 11V

LX Leakage Current

VLX = 40V

260
MAX5025/MAX5026,
VFB = 1.4V

0.01

Ω

mA

10

µA

0.8

V

MAX5027/MAX5028,
VFB = 35V

LOGIC INPUT: SHDN
Input Low Level

VIL

Input High Level

VIH

Input Bias Current

2.4
-1

V
1

µA

Note 1: All devices are 100% production tested at TA = +25°C. All temperature limits are guaranteed by design.
Note 2: Switch current-limit accuracy is typically ±20% and is a function of the input voltage. ILIM = (VIN/5) (260mA).

_______________________________________________________________________________________

3

Typical Operating Characteristics
(VCC = 5V, VOUT = 30V, TA = +25°C, unless otherwise noted.)
EFFICIENCY vs. LOAD CURRENT
(VOUT = 12V)

40
MAX5026
VCC = 5V,
VOUT = 12V
CIRCUIT OF FIGURE 2.
R1 = 147kΩ, R2 = 16.2kΩ

30
20
10

80
70

40
MAX5026
VCC = 5V,
VOUT = 12V
CIRCUIT OF FIGURE 2.
R1 = 147kΩ, R2 = 13kΩ

30

10

60

2

4

6

8

10

MAX5026
VCC = 5V,
VOUT = 24V
CIRCUIT OF FIGURE 2.
R1 = 147kΩ, R2 = 8.07kΩ

10
0

0

2

4

6

8

0

1

2

3

4

5

LOAD CURRENT (mA)

EFFICIENCY vs. LOAD CURRENT
(VOUT = 30V)

MAX5026 MINIMUM STARTUP VOLTAGE
vs. LOAD CURRENT

MAX5026/MAX5028
SUPPLY CURRENT vs. SUPPLY VOLTAGE

MAX5026
VCC = 5V,
VOUT = 30V
CIRCUIT OF FIGURE 2.
R1 = 147kΩ, R2 = 6.34kΩ

10

2

3

2.5
2.0
1.5

400
350
300
250
200
150
100

0.5

50

0

0
0

4

MAX5025-28 toc06

450

1.0

0
1

3.0

500

SUPPLY CURRENT (μA)

30
20

3.5
STARTUP VOLTAGE (V)

40

MAX5025-28 toc05

4.0

MAX5025-28 toc04

50

1

2

3

4

CURRENT INTO VCC PIN
DEVICE NOT SWITCHING
0

3

6

9

12

LOAD CURRENT (mA)

SUPPLY VOLTAGE (V)

MAX5026
NO LOAD SUPPLY CURRENT
vs. SUPPLY VOLTAGE

SUPPLY CURRENT vs. TEMPERATURE

MAX5026
SWITCHING FREQUENCY vs. TEMPERATURE

8
6
4

VCC = 11V

750

VCC = 9V

650

VCC = 7V
550

VCC = 5V

450

VCC = 3V

350
250

2

CURRENT INTO VCC PIN
150

0
5

7
SUPPLY VOLTAGE (V)

9

11

650
VCC = 5V
VOUT = 30V
CIRCUIT OF FIGURE 2.

600
SWITCHING FREQUENCY (kHz)

10

MAX5025-28 toc08

12

850

SUPPLY CURRENT (μA)

MAX5025-28 toc07

CIRCUIT OF FIGURE 2
VOUT = 30V

550
500
450
400
350
300
250
200

-40

-20

0

20

40

TEMPERATURE (°C)

60

80

-40

-20

0

20

40

TEMPERATURE (°C)

_______________________________________________________________________________________

60

80

MAX5025-28 toc09

LOAD CURRENT (mA)

16

3

30

LOAD CURRENT (mA)

60

14

40

LOAD CURRENT (mA)

70

0

50

20

0
0

EFFICIENCY (%)

50

20

0

4

60

70

EFFICIENCY (%)

50

80

MAX5025-28 toc03

90

EFFICIENCY (%)

60

EFFICIENCY vs. LOAD CURRENT
(VOUT = 24V)
MAX5025-28 toc02

70
EFFICIENCY (%)

EFFICIENCY vs. LOAD CURRENT
(VOUT = 15V)
MAX5025-28 toc01

90
80

NO LOAD SUPPLY CURRENT (mA)

MAX5025–MAX5028

500kHz, 36V Output, SOT23,
Step-Up DC-DC Converters

500kHz, 36V Output, SOT23,
Step-Up DC-DC Converters

EXITING SHUTDOWN

ENTERING SHUTDOWN

MAX5025-28 toc10

OUTPUT
VOLTAGE
20V/div

MAX5025-28 toc11

30V
30V

5V

INDUCTOR
CURRENT
50mA/div
5V

OUTPUT
VOLTAGE
20V/div

5V

SHUTDOWN
VOLTAGE
5V/div

5V
0V

SHUTDOWN
VOLTAGE
5V/div
2ms/div

100ms/div

MAX5026, VCC = 5V, VOUT = 30V, ILOAD = 1mA.
CIRCUIT OF FIGURE 3

MAX5026, VCC = 5V, VOUT = 30V, ILOAD = 1mA.
CIRCUIT OF FIGURE 3

LIGHT-LOAD SWITCHING WAVEFORM
WITHOUT RC FILTER

LIGHT-LOAD SWITCHING WAVEFORM
WITH RC FILTER

MAX5025-28 toc12

MAX5025-28 toc13

VOUT
2mV/div
AC-COUPLED

VOUT
1mV/div
AC-COUPLED

LX PIN
20V/div

LX PIN
20V/div
0V

IL
100mA/div

0mA

0V

IL
100mA/div

1μs/div

0mA

1μs/div

MAX5026, VCC = 5V, VOUT = 30V, ILOAD = 0.1mA.
CIRCUIT OF FIGURE 2

MAX5026, VCC = 5V, VOUT = 30V, ILOAD = 0.1mA.
CIRCUIT OF FIGURE 3

MEDIUM-LOAD SWITCHING WAVEFORM
WITHOUT RC FILTER

MEDIUM-LOAD SWITCHING WAVEFORM
WITH RC FILTER
MAX5025-28 toc15

MAX5025-28 toc14

VOUT
5mV/div
AC-COUPLED

VOUT
1mV/div
AC-COUPLED

LX PIN
20V/div

LX PIN
20V/div
0V

0V

IL
200mA/div

0mA

1μs/div
MAX5026, VCC = 5V, VOUT = 30V, ILOAD = 2mA.
CIRCUIT OF FIGURE 2

IL
200mA/div

0mA

1μs/div
MAX5026, VCC = 5V, VOUT = 30V, ILOAD = 2mA.
CIRCUIT OF FIGURE 3

_______________________________________________________________________________________

5

MAX5025–MAX5028

Typical Operating Characteristics (continued)
(VCC = 5V, VOUT = 30V, TA = +25°C, unless otherwise noted.)

Typical Operating Characteristics (continued)
(VCC = 5V, VOUT = 30V, TA = +25°C, unless otherwise noted.)
HEAVY-LOAD SWITCHING WAVEFORM
WITHOUT RC FILTER

HEAVY-LOAD SWITCHING WAVEFORM
WITH RC FILTER

MAX5025-28 toc16

MAX5025-28 toc17

VOUT
5mV/div
AC-COUPLED

VOUT
1mV/div
AC-COUPLED

LX PIN
20V/div

LX PIN
20V/div
0V

IL
200mA/div

0mA

0V

IL
200mA/div

0mA

1μs/div

1μs/div

MAX5026, VCC = 5V, VOUT = 30V, ILOAD = 4mA.
CIRCUIT OF FIGURE 2

MAX5026, VCC = 5V, VOUT = 30V, ILOAD = 4mA.
CIRCUIT OF FIGURE 3

LOAD TRANSIENT RESPONSE

LINE TRANSIENT RESPONSE

MAX5025-28 toc18

MAX5025-28 toc19

OUTPUT
VOLTAGE
200mV/div
AC-COUPLED

OUTPUT
VOLTAGE
1mV/div
AC-COUPLED
0mV

LOAD
CURRENT
10mA/div

0mA

0mV
INPUT
VOLTAGE
100mV/div
AC-COUPLED
0mV

1ms/div

2ms/div

MAX5026, VCC = 5V, VOUT = 30V, ILOAD = 0 TO 4mA.
CIRCUIT OF FIGURE 2

MAX5026, VCC = 5V TO 5.2V, VOUT = 30V, ILOAD = 1mA.
CIRCUIT OF FIGURE 2

MAX5028
FB PIN VOLTAGE vs. TEMPERATURE
MAX5025-28 toc20

1.270
1.265
VCC = 11V
VCC = 5V
1.255
1.250
VCC = 3V

1.245

30.2
VCC = 11V

30.0
29.8

VCC = 5V

29.6

1.240

29.4

1.235

29.2

1.230

VCC = 3V

29.0
-40

6

30.4

FB PIN VOLTAGE (V)

1.260

MAX5025-28 toc21

MAX5026
FB PIN VOLTAGE vs. TEMPERATURE

FB PIN VOLTAGE (V)

MAX5025–MAX5028

500kHz, 36V Output, SOT23,
Step-Up DC-DC Converters

-20

0

20

40
TEMPERATURE (°C)

60

80

-40

-20

0

20

40

TEMPERATURE (°C)

_______________________________________________________________________________________

60

80

500kHz, 36V Output, SOT23,
Step-Up DC-DC Converters

SWITCH ON-RESISTANCE
vs. TEMPERATURE

LX LEAKAGE CURRENT vs. TEMPERATURE

2.5

2.0
VCC = 5V

1.5

0.040
0.035
0.030
0.025
0.020
0.015
0.010

1.0

0.005

VCC = 11V

0

0.5
0

20

40

60

0

20

40

60

TEMPERATURE (°C)

LOAD REGULATION

MAX5026
MAXIMUM LOAD CURRENT
vs. INPUT VOLTAGE

MAX5026
VCC = 5V
WITHOUT RC FILTER
(CIRCUIT OF FIGURE 2)

30
WITH RC FILTER
(CIRCUIT OF FIGURE 3)

29

-20

TEMPERATURE (°C)

32

31

-40

80

28

80

100
MAXIMUM LOAD CURRENT (mA)

-20

MAX5025-28 toc24

-40

OUTPUT VOLTAGE (V)

CURRENT INTO LX PIN
VLX = 40V

0.045

MAX5025-28 toc25

RON (Ω)

VCC = 3V

MAX5025-28 toc23

MAX5026

0.050

LX LEAKAGE CURRENT (μA)

MAX5025-28 toc22

3.0

A
B

10
C

D
E
A: VOUT = 12V
B: VOUT = 24V
C: VOUT = 30V
D: VOUT = 32V
E: VOUT = 36V

1

0.1
0

1

2

3

LOAD CURRENT (mA)

4

5

3

5

7

9

11

INPUT VOLTAGE (V)

_______________________________________________________________________________________

7

MAX5025–MAX5028

Typical Operating Characteristics (continued)
(VCC = 5V, VOUT = 30V, TA = +25°C, unless otherwise noted.)

MAX5025–MAX5028

500kHz, 36V Output, SOT23,
Step-Up DC-DC Converters
Pin Description
PIN
MAX5025/
MAX5026

MAX5027/
MAX5028

NAME

FUNCTION

1

1

PGND

Power Ground. Connect directly to local ground plane. Use a star ground configuration
for low noise.

2

2

GND

Ground. Connect directly to local ground plane.

3

—

FB

Feedback Pin. Reference voltage is approximately 1.25V. Connect resistive-divider tap
here. Minimize trace area at FB. See Setting the Output Voltage section.

—

3

FB

Feedback Pin. Connect VOUT to FB for +30V. Internal resistors divide down the output
voltage.

4

4

SHDN

5

5

VCC

6

6

LX

Shutdown Pin. Connect to VCC to enable device. Connect to GND to shut down.
Input Supply Voltage. Bypass with a 4.7µF ceramic capacitor.
Drain of Internal 40V N-Channel DMOS. Connect inductor/diode to LX. Minimize trace
area at this pin to keep EMI down.

Detailed Description
The MAX5025–MAX5028 current-mode PWM controllers operate in a wide range of DC-DC conversion
applications including boost, flyback, and isolated output configurations. These converters provide lownoise, high output voltages making them ideal for varactor diode tuning applications as well as TFT LCD
bias. Other features include shutdown, fixed 500kHz
PWM oscillator, and a wide input range: 3V to 11V for
MAX5026/MAX5028 and 4.5V to 11V for MAX5025/
MAX5027.
The MAX5025–MAX5028 operate in discontinuous
mode in order to reduce the switching noise at the output. Other continuous mode boost converters generate
a large voltage spike at the output when the LX switch
turns on because there is a conduction path between
the output, diode, and switch to ground during the time
needed for the diode to turn off.
To reduce the output noise even further, the LX switch
turns off by taking 40ns typically to transition from “ON”
to “OFF.” As a consequence, the positive slew rate of
the LX node is reduced and the current from the inductor does not “force” the output voltage as hard as
would be the case if the LX switch were to turn off more
quickly.

PWM Controller
The heart of the MAX5025–MAX5028 current-mode
PWM controllers is a BiCMOS multi-input comparator
that simultaneously processes the output-error signal
and switch current signal. The main PWM comparator
8

is direct summing, lacking a traditional error amplifier
and its associated phase shift. The direct summing
configuration approaches ideal cycle-by-cycle control
over the output voltage since there is no conventional
error amp in the feedback path.
The device operates in PWM mode using a fixed-frequency, current-mode operation. The current-mode
feedback loop regulates peak inductor current as a
function of the output error signal.

SHDN Input
The SHDN pin provides shutdown control. Connect
SHDN to V CC for normal operation. To disable the
device, connect SHDN to GND.

Design Procedure
The MAX5025–MAX5028 can operate in a number of
DC-DC converter configurations including step-up, single-ended primary inductance converter (SEPIC), and
flyback. The following design discussions are limited to
step-up, with a complete circuit shown in the
Application Circuits section.

Setting the Output Voltage
The output voltage of the MAX5027/MAX5028 is fixed
at 30V. The output voltage of the MAX5025/MAX5026 is
set by two external resistors (R1 and R2, Figure 2 and
Figure 3). First select the value of R2 in the 5kΩ to
50kΩ range. R1 is then given by:

_______________________________________________________________________________________

500kHz, 36V Output, SOT23,
Step-Up DC-DC Converters
ULVO

3

FB

-A

OSCILLATOR

MAIN PWM
COMPARATOR

SHDN

4

LX

6

PGND

1

CONTROL
LOGIC

+A

REF

THERMAL
SHUTDOWN

+C
2

GND

5

VCC

-C

CURRENTLIMIT
COMPARATOR

N

L =
MAX5025
MAX5026

Figure 1. Functional Diagram

Use the following formula to calculate the upper bound
of the inductor value at different output voltages and
output currents. This is the maximum inductance value
for discontinuous mode operation.
LUPPER =

⎛V
⎞
R1 = R2 ⎜ OUT - 1⎟
⎝ VREF ⎠
where VREF is 1.25V

Determining Peak Inductor Current
If the boost converter remains in the discontinuous
mode of operation, then the approximate peak inductor
current, ILPEAK, is represented by the formula below:
ILPEAK =

2 TS ( VOUT − VIN ) IOUT
ηL

where TS is the period, VOUT is the output voltage, VIN
is the input voltage, IOUT is the output current, and η is
the efficiency of the boost converter.

(47μH) (VOUT − VIN )
(25V)

2
VIN
(VOUT − VIN ) TSη
2
2 IOUT VOUT

Calculate the lower bound, LLOWER, for the acceptable
inductance value using the following formula, which will
allow the maximum output current to be delivered without reaching the peak current limit:
LLOWER =

2 TS ( VOUT − VIN ) IOUT
⎛V
⎞
η ⎜ IN (260mA)⎟
⎝ 5
⎠

2

Notice that the switch current limit, (VIN/5)(260mA), is a
function of the input voltage, VIN. The current rating of
the inductor should be greater than the switch current
limit.

Table 1. Inductor Vendors
VENDOR

PHONE

FAX

PART NUMBER OF 47µH INDUCTOR

Coilcraft

847-639-6400

847-639-1469

DT1608C-473

Sumida

847-545-6700

847-545-6720

CDRH4D28-470

Toko

847-297-0070

847-699-7864

A915BY-470M

_______________________________________________________________________________________

9

MAX5025–MAX5028

Determining the Inductor Value
47µH is the recommended inductor value when the output voltage is 30V and the input voltage is 5V. In general, the inductor should have a current rating greater
than the current-limit value. For example, the inductor’s
current rating should be greater than 150mA to support
a 4mA output current. Equivalent series resistance
(ESR) should be below 1Ω for reasonable efficiency.
Due to the MAX5025–MAX5028’s high switching frequency, inductors with a ferrite core or equivalent are
recommended. Powdered iron cores are not recommended due to their high losses at frequencies over
500kHz. Table 1 shows a list of vendors and 47µH
inductor parts.
For 4mA output current and output voltages other than
30V, the inductor can be simply scaled in value
according to the following formula:

MAX5025–MAX5028

500kHz, 36V Output, SOT23,
Step-Up DC-DC Converters
Capacitor Selection

For a design in which VIN = 5V, VOUT = 30V, IOUT =
4mA, η = 0.5, and TS = 2µs,
LUPPER = 87µH

Output Filter Capacitor
The output filter capacitor should be 1µF or greater. To
achieve low output ripple, a capacitor with low ESR, low
ESL, and high capacitance value should be selected.
For very low output ripple applications, the output of the
boost converter can be followed by an RC filter to further reduce the ripple. Figure 3 shows a 100Ω, 1µF filter used to reduce the switching output ripple to
1mVp-p.
X7R ceramic capacitors are better for this boost application because of their low ESR and tighter tolerance
over temperature than the Y5V ceramic capacitors.
Table 3 below lists manufacturers of recommended
capacitors.

and
LLOWER = 12µH.
For a worst-case scenario in which VIN = 4.75V, VOUT
= 29V, IOUT = 4.4mA, η = 0.5, and TS = 1.25µs,
LUPPER = 46µH
and
LLOWER = 9µH.
The choice of 47µH as the recommended inductance
value is reasonable given the worst-case scenario
above. In general, the higher the inductance, the lower
the switching noise. Load regulation is also better with
higher inductance.

Input Capacitor
Bypass VCC with a 4.7µF ceramic capacitor as close to
the IC as is practical.

Diode Selection
The MAX5025–MAX5028’s high switching frequency
demands a high-speed rectifier. Schottky diodes are
recommended for most applications because of their
fast recovery time and low forward-voltage drop.
Ensure that the diode’s peak current rating is greater
than or equal to the peak inductor current. Also, the
diode reverse breakdown voltage must be greater than
VOUT. Table 2 lists diode vendors.

Applications Information
Layout Considerations
The MAX5025–MAX5028 switch at high speed, mandating careful attention to layout for optimum performance. Protect sensitive analog grounds by using a
star ground configuration. Minimize ground noise by
connecting GND, PGND, the input bypass-capacitor
ground lead, and the output-filter ground lead to a single point (star ground configuration). Also, minimize

Table 2. Schottky Diode Vendors
VENDOR

PHONE

FAX

PART NUMBERS

Comchip

510-657-8671

510-657-8921

CDBS1045

Panasonic

408-942-2912

408-946-9063

MA2Z785

ST-Microelectronics

602-485-6100

602-486-6102

TMMBAT48

Vishay-Telefunken

402-563-6866

402-563-6296

BAS382

Zetex

631-360-2222

631-360-8222

ZHCS500

Table 3. Capacitor Table
COMPANY

PHONE

FAX

Murata

814-237-1431

814-238-0490

Taiyo Yuden

408-573-4150

408-573-4159

TDK

10

847-803-6100

847-803-6296

PART NUMBERS
GRM42-2X7R105K050AD (1µF capacitor)
GRM32-1210R71C475R (4.7µF capacitor)
UMK325BJ105KH (1µF capacitor)
EMK316BJ475ML (4.7µF capacitor)
C3225X7R1H155K (1.5µF capacitor)
C3225X7R1H105K (1µF capacitor)

______________________________________________________________________________________

500kHz, 36V Output, SOT23,
Step-Up DC-DC Converters
Figures 2 and 3 show the MAX5025/MAX5026 operating in a 30V boost application. Figure 3 has an RC filter
to reduce noise at the output. These circuits provide
output currents greater than 4mA with an input voltage
of 5V or greater. They are designed by following the
Design Procedure section. Operating characteristics of
these circuits are shown in the Typical Operating
Characteristics section.

Inductor Layout
The shielded drum type inductors have a small air gap
around the top and bottom periphery. The incident fringing magnetic field from this air gap to the copper plane
on the PC board tends to reduce efficiency. This is a
result of the induced eddy currents on the copper plane.
To minimize this effect, avoid laying out any copper
planes under the mounting area of these inductors.

VCC = 4.5V TO 11V
(MAX5025)
VCC = 3V TO 11V
(MAX5026)

VCC

C1
4.7μF

L1 TOKO 47μH INDUCTOR
47μH A915BY-470M
ZETEX SCHOTTKY DIODE
D1 ZHCS500
VOUT
LX
+30V
R1
147kΩ

MAX5025
MAX5026
SHDN
FB

C2
1μF
R2
6.34kΩ

PGND GND

Figure 2. Adjustable 30V Output Circuit

VCC = 4.5V TO 11V
(MAX5025)
VCC = 3V TO 11V
(MAX5026)

VCC

C1
4.7μF

L1 TOKO 47μH INDUCTOR
47μH A915BY-470M
ZETEX SCHOTTKY DIODE R3
100Ω
D1 ZHCS500
LX

MAX5025
MAX5026
SHDN
FB
PGND GND

VOUT
+30V

R1
147kΩ
C2
1μF

C3
1μF

R2
6.34kΩ

Figure 3. Adjustable 30V Output Circuit with RC Filter

______________________________________________________________________________________

11

MAX5025–MAX5028

30V Boost Application Circuit

trace lengths to reduce stray capacitance, trace resistance, and radiated noise. The trace between the output voltage-divider (MAX5025/MAX5026) and the FB
pin must be kept short, as well as the trace between
GND and PGND.

MAX5025–MAX5028

500kHz, 36V Output, SOT23,
Step-Up DC-DC Converters
Selector Guide
PART

OUTPUT

FREQUENCY
TOLERANCE

FB SET POINT
TOLERANCE

INPUT VOLTAGE

MAX5025

Adjustable

-31% to +100%

±5%

4.5V to 11V

MAX5026

Adjustable

-18% to +34%

±3%

3V to 11V

MAX5027

Fixed 30V

-31% to +100%

±5%

4.5V to 11V

MAX5028

Fixed 30V

-18% to +34%

±3%

3V to 11V

Package Information

____________________Chip Information
TRANSISTOR COUNT: 365
PROCESS: BiCMOS

12

For the latest package outline information and land patterns, go
to www.maxim-ic.com/packages.
PACKAGE TYPE

PACKAGE CODE

DOCUMENT NO.

6 SOT23

S8-2

21-0058

______________________________________________________________________________________

500kHz, 36V Output, SOT23,
Step-Up DC-DC Converters
REVISION
NUMBER

REVISION
DATE

DESCRIPTION

PAGES
CHANGED

0

10/01

Initial release

—

1

12/01

Released the MAX5027

1

2

3/09

Revised the Absolute Maximum Ratings section.

2

Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.

Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 13
© 2009 Maxim Integrated Products

Maxim is a registered trademark of Maxim Integrated Products, Inc.

MAX5025–MAX5028

Revision History

www.s-manuals.com



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