UC3842A Просмотр технического описания (PDF) - Fairchild Semiconductor

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UC3842A

SMPS Controller

Fairchild Semiconductor 

UC3842A/UC3843A

SMPS Controller

www.fairchildsemi.com

Features

• Low Start Current 0.2mA (typ)

• Operating Range Up To 500KHz

• Cycle by Cycle Current Limiting

• Under Voltage Lock Out With Hysteresis

• Short Shutdown Delay Time: typ.100ns

• High Current Totem-pole Output

• Output Swing Limiting: 22V

Description

The UC3842A/UC3843A are fixed PWM controller for Off-

Line and DC to DC converter applications. The internal cir-

cuits include UVLO, low start up current circuit, tempera-

ture compensated reference, high gain error amplifier,

current sensing comparator, and high current totem-pole out-

put for driving a POWER MOSFET. Also UC3842A/

UC3843A provide low start up current below 0.3mA and

short shutdown delay time typ. 100ns. The UC3842A has

UVLO threshold of 16V(on) and 10V(off). The UC3843A is

8.4V(on) and 7.6V(off). The UC3842A and UC3843A can

operate within 100% duty cycle.

8-DIP

Internal Block Diagram

1

8-SOP

1

VREF 8

Internal

Bias

5V

VREF

SET/

RESET

Good LOGIC

UVLO

VFB 2

COMP 1

1/2VREF

Error Amp

+

-

1/3

1V

C.S PWM

Comp. LATCH

R

S

C.S 3

T

RT/CT 4

OSCILLATOR

7 VCC

29V

5 GND

7

PWR

VC

22V 6 OUTPUT

5

PWR

GND

©2000 Fairchild Semiconductor International

Rev. 5.0

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