FEATURES

Low Output Jitter

Soft−Stop Shutdown of MAIN and AUX

Ideal for Active Clamp/Reset Forward,

Flyback Converters

Provides Complementary Auxiliary Driver

with Programmable Deadtime (Turn-On

Delay) between AUX and MAIN Switches

Peak Current-Mode Control with

Cycle-by-Cycle Current Limiting

110-V Input Startup Regulator on UCC2891/3

TrueDrive 2-A Sink, 2-A Source Outputs

Accurate Line UV and Line OV Threshold

Programmable Slope Compensation

1.0-MHz Synchronizable Oscillator

Precise Programmable Maximum Duty Cycle

Programmable Soft Start

APPLICATIONS

150-W to 700-W SMPS

High-Efficiency, Low EMI/RFI Off-Line or

DC/DC Converters

Server, 48-V Telecom, Datacom

High Power Adapter, LCD-TV and PDP-TV

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, fixedfrequency,

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,

precise DMAX limit, and a single resistor

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.