UCC2897
SLUS591A − NOVEMBER 2003 − REVISED MARCH 2004
ADVANCED CURRENT MODE
ACTIVE CLAMP PWM CONTROLLER
FEATURES
D
Ideal for Active Clamp/Reset Forward,
D
D
D
D
D
D
D
D
D
D
Flyback and Synchronous Rectifier Apps
Provides Complementary Auxiliary Driver
with Programmable Deadtime (Turn-On
Delay) between AUX and MAIN Switches
Peak Current-Mode Control with 0.5-V
Cycle-by-Cycle Current Limiting
Hiccup Mode 0.75-V Current Limit
TrueDrivet 2-A Sink, 2-A Source Outputs
110-V Input Startup Device
Trimmed Internal Bandgap Reference for
Accurate Line UV and Line OV Threshold
Programmable Slope Compensation
High-Performance 1.0-MHz Synchronizable
Oscillator with Internal Timing Capacitor
Precise Programmable Maximum Duty Cycle
PB-Free Lead Finish Package
DESCRIPTION
The UCC2897 PWM controller simplifies
implementation of the various active clamp/reset
and synchronous rectifier switching power
topologies.
Based on the UCC2891 active-clamp controller
the UCC2897 is a peak current-mode, fixed-
frequency, high-performance pulse width modulator.
It includes the logic and the drive capability for the
P-channel auxiliary switch along with a simple
method of programming the critical delays for
proper active clamp operation.
Features include an internal programmable slope
compensation circuit, precise D
MAX
limit, and a
synchronizable oscillator with an internal timing
capacitor. An accurate line monitoring function
also programs the converter’s ON and OFF
transitions with regard to the bulk input voltage.
The UCC2897 adds a second level hiccup mode
current
sense
threshold,
bi-directional
synchronization and the input overvoltage
protection functionalities that are not available on
the 16-pin UCC2891. The UCC2897 is offered in
20-pin TSSOP (PW) package.
APPLICATIONS
D
High-Efficiency DC/DC Power Supplies
D
Server Power, 48-V Telecom, Datacom, and
42-V Automotive Applications
TYPICAL APPLICATION DIAGRAM
UCC2897
3
4
5
6
7
8
9
10
12
RDEL
VIN
LINEOV
RTON
LINEUV
RTOFF
VDD
VREF
PVDD
SYNC
GND
CS
OUT
AUX
14
13
11
RF
RCS
SECONDARY
SIDE E/A
UDG−03186
16
Q2
15
17
CCLAMP
Q1
SR
DRIVE
1
19
LOAD
18
BIAS
WINDING
CBULK
+VIN
RSLOPE PGND
SS/SD
FB
These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
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
2004, Texas Instruments Incorporated
www.ti.com
1
TI [ TEXAS INSTRUMENTS ]
