UCC2891, UCC2892

UCC2893, UCC2894

SLUS542A − OCTOBER 2003 − REVISED JULY 2004

CURRENT MODE

ACTIVE CLAMP PWM CONTROLLER

1

www.ti.com

FEATURES

Flyback Converters

with Programmable Deadtime (Turn-On

Delay) between AUX and MAIN Switches

Cycle-by-Cycle Current Limiting

APPLICATIONS

DC/DC Converters

DESCRIPTION

The UCC2891/2/3/4 family of PWM controllers is

designed to simplify implementation of the various

active clamp/reset switching power topologies.

The UCC289x is a peak current-mode, fixed-

frequency, high-performance pulse width modulator.

It includes the logic and the drive capability for the

auxiliary

switch

with

a

simple

method

of

programming the critical delays for proper active

clamp operation.

The UCC2891/3 includes a 110-V start-up

regulator for initial start-up and to provide

keep-alive power during stand-by.

Additional

features

include

an

internal

programmable

slope

compensation

circuit,

programmable

synchronizable

oscillator.

An

accurate line monitoring function also programs

the converter’s ON and OFF transitions with

regard to the bulk input voltage. Along with the

UCC2897, this UCC289x family allows the power

supply designer to eliminate many of the external

components, reducing the size and complexity of

the design.

CBULK

RCS

UDG−02162

CCLAMP

RF

5

13

12

16

15

1

2

3

RDEL

RTON

RTOFF

SYNC

LINEUV

OUT

AUX

PGND

4

VREF

11

VIN

UCC2891

6

GND

7CS

8

RSLOPE

14

VDD

SS/SD

10

FB

9

SECONDARY

SIDE E/A

Q1

Q2

LOAD

SR

DRIVE

BIAS

WINDING

+VIN

PRODUCTION DATA information is current as of publication date.

Products conform to specifications per the terms of Texas Instruments

standard warranty. Production processing does not necessarily include

testing of all parameters.

Copyright

 2003, Texas Instruments Incorporated

Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of

Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.