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.