Chip-Rail CR6848S, CR6848T Schematics

Novel Low Cost Green-Power PWM Controller

Features

z Low Cost, PWM&PFM&CRM
z Low Start-up Current (about 10µA)
z Low Operating Current (about 2mA)
z Current Mode Operation
z Under Voltage Lockout (UVLO)
z Built-in Synchronized Slope

Compensation

z Programmable PWM Frequency

z Leading edge Blanking on Sense input

z Constant output power limiting for

Applications

z Switching AC/DC Adaptor
z 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

CR6848

universal AC input

z Cycle-by-cycle current limiting
z Clamped gate output voltage 16.5V
z Over voltage protect 26.7V
z High-Voltage CMOS Process with ESD
z SOT-23-6L、SOP-8 & DIP-8 Pb-Free

Packaging

z Compatible with SG5701 & SG5848 &

LD7535 &OB22632/63

z Open Frame Switching Power Supply
z 384X Replacement

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.

Dec, 2006 V1.5 1/14

Chengdu Chip-Rail Tech.Co.Ltd. http://www.chiprail.com

CR6848

CR68XX Series

Part

Number

CR6848

CR6850

CR6851

PWM

Frequency

External
Adjustable

External
Adjustable

External
Adjustable

DIP-8、SOP8
SOT-23-6L

DIP-8、SOP8
SOT-23-6L

DIP-8、SOP8
SOT-23-6L

TYPICAL APPLICATION

Package 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

Dec, 2006 V1.5 2/14

Chengdu Chip-Rail Tech.Co.Ltd. http://www.chiprail.com

CR6848

Pin Assignment

Pin Descriptions

Name Description

GND GND Pin

FB

RI

SEN

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 Gate output to drive the external power MOSFET.

Supply voltage pin.

Block Diagram

Simplified Internal Circuit Architecture

Dec, 2006 V1.5 3/14

Chengdu Chip-Rail Tech.Co.Ltd. http://www.chiprail.com

CR6848

Absolute Maximum Ratings

Symbol Parameter Rating Unit

V

DD

I

OVP

V

FB

V

SEN

P

D

T

L

T

STG

Supply voltage Pin Voltage 40 V

VDD OVP maximal enter current 20 mA

Input Voltage to FB Pin -0.3 to 6V V

Input Voltage to SEN Pin -0.3 to 6V V

Power Dissipation 300 mW

ESD Capability, HBM Model 2000 V

ESD Capability, Machine Model 200 V

Lead Temperature
(Soldering)

Storage Temperature Range -55 to + 150

20 second
SOT-23-6L

10 second
DIP-8

220

260

RECOMMENDED OPERATION CONDITION

Symbol Parameter Min ~ Max Unit

℃

℃
℃

VDD VDD Supply Voltage 11~20 V

RI RI PIN Resistor Value 58~120 K ohm

TOA Operation Ambient Temperature -20~85

℃

PO Output Power 0~60 W

F

PWM

Frequency of PWM 48~100 kHz

Dec, 2006 V1.5 4/14

Chengdu Chip-Rail Tech.Co.Ltd. http://www.chiprail.com

CR6848

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

Symbol Parameter Conditions Min. Typ. Max. Unit
Supply Voltage (VDD Pin)

I

ST

Startup Current 10

µA

VFB=0V 2.8 mA

I

VDD

VDD

VD

SS

CLAMP

Operating Current

Turn-on Threshold Voltage 16.1 V

ON

Turn-off Threshold Voltage 11.1 V

OFF

VDD Clamp Voltage I

VFB=3V 2.3 mA

=Open 1.46 mA

V

FB

=20mA 26.7 V

VDD

Voltage Feedback (FB Pin)

IFB Short Circuit Current VFB=0V 2.8 mA

VFB Open Loop Voltage VFB=Open 4.8 V

I

Enter PFM, FB current 0.92 mA

PFM

I

CRM

Enter CRM, FB current 1.5 mA

Current Sensing (SEN Pin)

V

V

TH_L

TH_H

Minimum Voltage Lever 0.83 0.87 V

Maximum Voltage Lever 1.0 1.05 V

TPD Delay to Output 300 ns

RCS Input Impedance

50 KΩ

Oscillator (RI Pin)

F

Normal Frequency RI=100Kohm 53 58 63 KHz

OSC

F

PFM Frequency RI=100Kohm 11.6 KHZ

PFM

DC

Maximum Duty Cycle RI=100Kohm 75 %

MAX

ΔF

T

Frequency Temp. Stability

TEMP

Leading-Edge Blanking Time 300 nS

BLANK

-30-85

℃

5 %

GATE Drive Output (GATE Pin)

VG

V

OL

V

OH

T

T

CLAMP

Output Low Level VDD=15V, IO=20mA 1 V

Output High Level VDD=15V, IO=20mA 8 V

Rising Time

R

Falling Time CL=1000pF 130 ns

F

CL=1000pF 450 ns

Output Clamp Voltage VDD=20V 16.5 V

Dec, 2006 V1.5 5/14

Chengdu Chip-Rail Tech.Co.Ltd.
http://www.chiprail.com