UCC2891DRG4 Datasheet, PDF (1/41 Pages) Texas Instruments – 
CURRENT-MODE ACTIVE CLAMP PWM CONTROLLER

UCC2891, UCC2892
UCC2893, UCC2894
ą
SLUS542F − OCTOBER 2003 − REVISED JULY 2009
CURRENTĆMODE
ACTIVE CLAMP PWM CONTROLLER
FEATURES
DESCRIPTION
D Low Output Jitter
D Soft−Stop Shutdown of MAIN and AUX
D Ideal for Active Clamp/Reset Forward,
Flyback Converters
D Provides Complementary Auxiliary Driver
with Programmable Deadtime (Turn-On
Delay) between AUX and MAIN Switches
D Peak Current-Mode Control with
Cycle-by-Cycle Current Limiting
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.
D 110-V Input Startup Regulator on UCC2891/3
D TrueDrivet 2-A Sink, 2-A Source Outputs
The UCC2891/3 includes a 110-V start-up
regulator for initial start-up and to provide
D Accurate Line UV and Line OV Threshold
keep-alive power during stand-by.
D Programmable Slope Compensation
Additional features include an internal
D 1.0-MHz Synchronizable Oscillator
D Precise Programmable Maximum Duty Cycle
D Programmable Soft Start
programmable slope compensation circuit,
precise D_MAX limit, and a single resistor
programmable synchronizable oscillator. An
accurate line monitoring function also programs
the converter’s ON and OFF transitions with
APPLICATIONS
D 150-W to 700-W SMPS
D High-Efficiency, Low EMI/RFI Off-Line or
DC/DC Converters
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.
D Server, 48-V Telecom, Datacom
D High Power Adapter, LCD-TV and PDP-TV
RDEL
R _ON
ROFF
C _VREF
UCC2891
1 RDEL
VIN 16
2 RTON LINE UV 15
3 RTOFF VDD 14
4 VREF
OUT 13
5 SYNC
AUX 12
BIAS
WINDING
+VIN
C _BULK
C _BIAS
ROUT
Q1
C _CLAMP
D1
C _AUX
Q2
D2
Q4
D3
Q3
SR
DRIVE
Lo
D4 Co
LOAD
6 GND
PGND 11
CF
7 CS
SS/SD 10
8 RSLOPE
RSLOPE
FB 9
C _SS
D _AUX
RF
R _CS
SECONDARY
SIDE E/A
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.
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.
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Copyright  2003 − 2009, Texas Instruments Incorporated
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