CR6848 Datasheet. Www.s Manuals.com. Chip Rail

User Manual: Datasheets CR6848S, CR6848T.

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CR6848
Novel Low Cost Green-Power PWM Controller
Features
z
z
z
z
z
z
z
z

z

Low Cost, PWM&PFM&CRM
Low Start-up Current (about 10µA)
Low Operating Current (about 2mA)
Current Mode Operation
Under Voltage Lockout (UVLO)
Built-in Synchronized Slope
Compensation
Programmable PWM Frequency
Leading edge Blanking on Sense input
Constant output power limiting for

z
z
z
z

universal AC input
Cycle-by-cycle current limiting
Clamped gate output voltage 16.5V
Over voltage protect 26.7V
High-Voltage CMOS Process with ESD

z

SOT-23-6L、SOP-8 & DIP-8 Pb-Free

z

Packaging
Compatible with SG5701 & SG5848 &
LD7535 &OB22632/63

z
z

Open Frame Switching Power Supply
384X Replacement

Applications
z
z

Switching AC/DC Adaptor
Battery Charger

General Description
The CR6848 is a highly integrated low cost
current mode PWM controller, which is ideal
for small power current mode of offline
AC-DC fly-back converter applications.
Making use of external resistors, the IC
changes the operating frequency and
automatically enters the PFM/CRM under
light-load/zero-load conditions. This can
minimize standby power consumption and
achieve green-power functions. With a very
low start-up current, the CR6848 could use
a large value start-up resistor (1.5Mohm).
Built-in synchronized slope compensation
enhances the stability of the system and
avoids sub-harmonic oscillation. Dynamic
peak limiting circuit minimizes output power
change caused by delay time of the system
over a universal AC input range. Leading

Dec, 2006

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edge blanking circuit on current sense input
could remove the signal glitch due to
snubber circuit diode reverse recovery and
thus
greatly
reduces
the
external
component count and system cost in the
design. Pulse-by-pulse current limiting
ensures safe operation even during
short-circuit.
The CR6848 offers more protection like
OVP (Over Voltage Protection) and OCP
(Over current protection). The CR6848’s
output driver is clamped to maximum 16.5V
to protect the power MOSFET. Excellent
EMI performance is achieved soft switching
control at the totem pole gate driver output.
CR6848 is offered in SOT-23-6, SOP-8 and
DIP-8 packages.

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CR6848

CR68XX Series
Part
Number

PWM
Frequency

Package

CR6848

External
Adjustable

DIP-8、SOP8
SOT-23-6L

CR6850

External
Adjustable

DIP-8、SOP8
SOT-23-6L

CR6851

External
Adjustable

DIP-8、SOP8
SOT-23-6L

Description
PWM&PFM&CRM 、 Current Mode 、 Slope
Compensation Leading-edge Blanking 、 Gate
Clamped、Over-voltage Protection、Over-current
Protection、 Soft Drive.
With All Functions of CR6848 、 Gate soft
Clamped
With All Functions of CR6850、Frequency jitter、
Soft start、Sense Fault Protect、OLP、SCP、
OTP

TYPICAL APPLICATION

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CR6848

Pin Assignment

Pin Descriptions
Name
GND
FB

SEN

Description
GND Pin
Analog Input. Voltage feedback pin (same as the COMP pin in UC384X),
This pin is to program the switching frequency. By connecting a resistor
to ground to set the switching frequency.
Current sense pin, connect to sense the MOSFET current.

VDD
GATE

Supply voltage pin.
Gate output to drive the external power MOSFET.

RI

Block Diagram

Simplified Internal Circuit Architecture

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CR6848

Absolute Maximum Ratings
Symbol
VDD
IOVP
VFB
VSEN
PD

Parameter
Supply voltage Pin Voltage
VDD OVP maximal enter current
Input Voltage to FB Pin
Input Voltage to SEN Pin
Power Dissipation
ESD Capability, HBM Model
ESD Capability, Machine Model
20 second
Lead Temperature
SOT-23-6L
(Soldering)
10 second
DIP-8
Storage Temperature Range

TL

TSTG

Rating
40
20
-0.3 to 6V
-0.3 to 6V
300
2000
200

Unit
V
mA
V
V
mW
V
V

220

℃

260

℃

-55 to + 150

℃

RECOMMENDED OPERATION CONDITION
Symbol
VDD

VDD Supply Voltage

Min ~ Max

Unit

11~20

V

RI

RI PIN Resistor Value

58~120

K ohm

TOA

Operation Ambient Temperature

-20~85

℃

PO

Output Power

0~60

W

48~100

kHz

FPWM

Dec, 2006

Parameter

Frequency of PWM

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CR6848

Electrical Characteristics (Ta=25°C unless otherwise noted, VDD = 15V.)
Symbol

Parameter

Conditions

Min.

Typ.

Max.

Unit

Supply Voltage (VDD Pin)
IST

ISS

Startup Current

Operating Current

10

µA

VFB=0V

2.8

mA

VFB=3V

2.3

mA

VFB=Open

1.46

mA

VDDON

Turn-on Threshold Voltage

16.1

V

VDDOFF

Turn-off Threshold Voltage

11.1

V

VDCLAMP

VDD Clamp Voltage

IVDD=20mA

26.7

V

Voltage Feedback (FB Pin)
IFB

Short Circuit Current

VFB=0V

2.8

mA

VFB

Open Loop Voltage

VFB=Open

4.8

V

IPFM

Enter PFM, FB current

0.92

mA

ICRM

Enter CRM, FB current

1.5

mA

0.87

V

Current Sensing (SEN Pin)
VTH_L

Minimum Voltage Lever

0.83

VTH_H

Maximum Voltage Lever

1.0

TPD

Delay to Output

300

ns

RCS

Input Impedance

50

KΩ

1.05

V

Oscillator (RI Pin)
FOSC

Normal Frequency

RI=100Kohm

FPFM

PFM Frequency

RI=100Kohm

11.6

KHZ

DCMAX

Maximum Duty Cycle

RI=100Kohm

75

%

ΔFTEMP

Frequency Temp. Stability

-30-85℃

5

%

300

nS

TBLANK

53

Leading-Edge Blanking Time

58

63

KHz

GATE Drive Output (GATE Pin)
VOL

Output Low Level

VDD=15V, IO=20mA

VOH

Output High Level

VDD=15V, IO=20mA

TR

Rising Time

CL=1000pF

450

ns

TF

Falling Time

CL=1000pF

130

ns

Output Clamp Voltage

VDD=20V

16.5

V

VGCLAMP
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CR6848

TYPICAL CHARACTERISTICS

VDD startup Current VS Temperature

VDD startup Current VS Temperature

VDD (OFF) VS Temperature

VDD Operation Current VS Temperature

OVP VS Temperature

PWM frequency VS Temperature

Duty cycle VS Temperature
FOSC VS FB Current
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CR6848

FOSC VS RI pin resistor

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CR6848

OPERATION DESCRIPTION
Current Model
Compared to voltage model control,
current model control has a current
feedback loop. When the voltage of the
sense resistor peak current of the primary
winding reaches the internal setting value
VTH, comparator reverse, register reset and
power MOSFET cut-off. So that to detect
and modulate the peak current cycle by
cycle could control the output of the power
supply. The current feedback has a good
linear modulation rate and a fast input and
output dynamic impact avoid the pole that
the output filter inductance brings and the
second class system descends to first class
and so it widens the frequency range and
optimizes overload protection and short
circuit protection.

Startup Current and Under Voltage
Lockout
The startup current of CR6848 is set to be
very low so that a large value startup
resistor can therefore be used to minimize
the power loss. For AC to DC adaptor with
universal input range design, a 1.5 MΩ, 1/8
W startup resistor and a 10uF/25V VDD
hold capacitor could be used.
The turn-on and turn-off threshold of the
CR6848 is designed to 16.1V/11.1V. During
startup, the hold-up capacitor must be
charge to 16.1V through the startup resistor.
The hysteresis is implemented to prevent
the shutdown from the voltage dip during
startup.

Internal Bias and OSC Operation
A resistor connected between RI pin and
GND pin set the internal constant current
source to charge or discharge the internal
fixed cap. The charge time and discharge
time determine the internal clock speed and
the switching frequency. Increasing the
resistance will reduce the value of the input
current and reduce the switching frequency.
The relationship between RI pin and PWM
switching frequency follows the below
equation within the RI allowed range.

FOSC =

Green Power Operation
The power dissipation of switching mode
power supply is very important in zero load
or light load condition. The major dissipation
result from conduction loss、switching loss
and consume of the control circuit. However,
all of them related to the switching
frequency. There are many difference
topologies has been implemented in
different chip. The basic operation theory of
all these approaches intended to reduce the
switching frequency under light-load or
no-load condition.
CR6848`s green power function adapts
PWM、PFM and CRM combining modulation.
When RI resistor is 100k, the PWM
frequency is 58kHz in medium or heavy load
operation. Through modifying the pulse
width, CR6848 could control output voltage.
The current of FB pin increases when the
load is in light condition and the internal
mode controller enters PFM&PWM when
the feedback current is over 0.92mA. The
operation frequency of oscillator is to
descend gradually. The invariable frequency
of oscillator is 11.6kHz when the feedback
current is over 1.05mA. To decrease the
standby consumption of the power supply ,
Chip-Rail introduces the Cycle Reset Mode
technology；If the feedback current were
over 1.1mA, mode controller of CR6848
would reset internal register all the time and
cut off the gate pin, while the output voltage
is lower than the set value, it would set
register, gate pin operating again. Although
the frequency of the internal OSC is
invariable, the register would reset some
pulses so that the practical frequency is
decreased at the gate pin.

5800
(kHz )
RI ( KΩ)

For example, a 100kΩ resistor RI could
generate a 50uA constant current and a
58kHz PWM switching frequency. The
Dec, 2006

suggested operating frequency range of
CR6848 is within 48KHz to 100KHz.

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CR6848 Green-Power Function
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CR6848

Internal
Synchronized
Compensation

Slop

Although there are more advantages of the
current mode control than conventional
voltage mode control, there are still several
drawbacks of peak-sensing current-mode
converter. Especially the open loop
instability when it operates in higher than
50% of the duty-cycle. CR6848 is introduced
an internal slope compensation adding
voltage ramp to the current sense input
voltage for PWM generation to solve this
problem. It improves the close loop stability
greatly at CCM, prevents the sub-harmonic
oscillation and thus reduces the output
ripple voltage.

VSLOP = 0.33 ×

DUTY
= 0.4389 × DUTY
DUTYMAX

primary wind inductance. V IN ranges from
85VAC to 264VAC. To guarantee the output
power is a constant for universal input AC
voltage, there is a dynamic peak limit circuit
to compensate the system delay T that the
system delay brings on.

Leading-edge Blanking (LEB)
Each time the power MOSFET is switched
on, a turn-on spike will inevitably occur at
the sense pin, which would disturb the
internal signal from the sampling of the
RSENSE. There is a 300n sec leading edge
blanking time built in to avoid the effect of
the turn-on spike and the power MOSFET
cannot be switched off during this time. So
that the conventional external RC filtering on
sense input is no longer required.

Current Sensing & Dynamic peak
limiting
The current flowing by the power MOSFET
comes in to being a voltage VSENSE on the
sense pin cycle by cycle, which compares to
the internal reference voltage, controls the
reverse of the internal register, limits the
peak current IMAX of the primary of the
transformer. The energy E =

1
2
× L × I MAX
2

deposited by the transformer. So adjusting
the RSENSE can set the Max output power of
the power supple mode. The current flowing
by the power MOSFET has an extra value

∆I =

V IN
× TD due to the system delay T
LP

that the current detected from the sense pin
to power MOSFET cut off in the CR6848
(Among these, VIN is the primary winding
voltage of the transformer and LP is the

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Over Voltage Protection (OVP)
There is a 26.7V over-voltage protection
circuit in the CR6848 to improve the
credibility and extend the life of the chip. The
GATE is to shutdown immediately when the
voltage of the VDD is over 26.7V and the
voltage of VDD is to descend rapidly.

Gate Driver & Soft Clamped
CR6848’ output designs a totem pole to
drive a periphery power MOSFET. The dead
time is introduced to minimize the transfixion
current when the output is drove. The
NMOS is shut off when the other NMOS is
turned on. The clamp technology is
introduced to protect the periphery power
MOSFET from breaking down.

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CR6848

PACKAGE DEMENSIONS
DIP-8L

Dimensions

Symbol

Millimeters
Min.

Typ.

A

Max.

Min.

Typ.

5.334

A1

0.381

A2

3.175

0.210

3.302

3.429

0.125

0.130

b

1.524

0.060

0.457

0.018

9.017

E
E1

Max.

0.015

b1
D

9.271

10.160

0.355

7.620
6.223

6.350

L

2.921

eB
θ˚

0.365

0.135

0.400

0.300
6.477

0.245

0.250

3.302

3.810

0.115

0.130

0.150

8.509

9.017

9.525

0.335

0.355

0.375

0˚

7˚

15˚

0˚

7˚

15˚

e

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Inches

2.540

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0.100

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CR6848

SOT-23-6L

Symbol

Dec, 2006

Dimensions In Millimeters

Dimensions In Inches

Min

Max

Min

Max

A

0.700

1.000

0.028

0.039

A1

0.000

0.100

0.000

0.004

B

1.397

1.803

0.055

0.071

b

0.300

0.559

0.012

0.022

C

2.591

3.000

0.102

0.118

D

2.692

3.099

0.106

0.122

e

0.838

1.041

0.033

0.041

H

0.080

0.254

0.003

0.010

L

0.300

0.610

0.012

0.024

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CR6848

SOP-8L

Dimensions DISCLAIMERS
Symbol

Min.

A

1.346

A1

0.101

Millimeter
Typ.

b

0.053

0.254

0.004

E

3.810

e

1.016

0.069
0.010

0.008
4.978

1.270
0.381X45
°

Max.

0.016

0.203
4.648

F

Dec, 2006

Min.

1.752

0.406

c
D

Max.

Inch
Typ.

0.183

3.987

0.150

1.524

0.040

0.196
0.157
0.050
0.015X45
°

0.060

H

5.791

6.197

0.228

0.244

L

0.406

1.270

0.016

0.050

θ˚

0°

8°

0°

8°

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CR6848

REFERENCE CIRCUIT 1
CR6848 drives a periphery Power MOSFET.
5V/6A 30W Power Supply

Quantity

1
1
1
1
1
1
1
2
1
1
1
1
1
1
1
1

Part Number
C1
C2
C3
C4
C5
C7
C8
C6、C7
C8
BD1
D1
D2
D3
D4
T1
T2

Description

Quantity

102/1000V
103/1000V
104
33uF/400V
223/1000V
103/1000V
102/100V

1
1
1
2
1
1
1
1

1000 uF/25V
104
KBL406
FR107
1N4007
Y2010D
LED
20mH
EI-22

1
1
2
1
1
1
1

Part Number

Description

F1
L1
R1
R2、R3
R4
R5
R6

0.25A
10uH
20R
1K
100K
100K/0.5W
47R

R7
R8
R9
R11、R12
U1
U2
U3
Q1

1.5M
0R51
20R
3.3K
CR6848
PC817
TL431
2N60

Notice: Q1 is a Power MOSFET

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CR6848

REFERENCE CIRCUIT 2
CR6848 drives a periphery Power BJT（5V/3A 15W Power Supply）

Quantity

2
1
1
1
1
1
1
1
2
1
5
2
1
1
2
1
1
1

Part Number

Description

Quantity

C1、C2
C3
C4
C5
C6
C7
C8

104/400V
472
102
33uF/400V
10uF/50V
103/1000V
102/100V

C9
C10、C11
C12
D1、D2、D3、
D4、D5
D6、D7
D8
D9
D10、D11
T1
T2
F1

223/1000V
220uF/16V
1.0uF/16V
1N4007
1N4148
18V
SB560
FR107
20mH
EI-22
0.25A

Part Number

Description

1
1
1
1
2
1
1
2

R2
R3
R4
R5
R6、R7
R8
R9

100K
100K/0.5W
1K
1.5M
220R/1W
220R
20K

1
1

R12
R13

20R
1R2/1W
20K

1
1
1
1
1
1
1

R14
U1
U2
U3
U4
Q1
Q2

2K2
CR6848
PC817
TL431
LM358
13003
9013

R10、R11

Notice: Q1 is a Power BJT
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