UCC2960 Datasheet, PDF (1/12 Pages) Texas Instruments – PRIMARY-SLIDE STARTUP CONTROLLER

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D Operates With Secondary-Side PWM
Control
D Receives Isolated PWM Command Through
a Pulse-Edge-Transformer
D Initial Free-Running Soft-Start Up with
Duty-Cycle Clamping
D Up to 400-kHz Synchronizable Switching
Frequency
D High-Current FET Drive (1.5-A Sink, 0.75-A
Source)
D Overcurrent Protection
D Undervoltage Lockout with 2-V Hysteresis
D Low-Current Startup
UCC2960, UCC3960
PRIMARYĆSIDE STARTUP CONTROLLER
SLUS430A – APRIL 1999 – REVISED DECEMBER 2000
typical operating circuit
X
VIN
UCC3960
2 FB
FEED
BACK
1 SS
VDD 8
REF 4
SOFT
START
OUT 7
3 RT
FREQ
SET
CS 5
GND 6
UDG–99010
description
Figure 1
The UCC3960 primary-side startup controller is a unique solution that provides all the primary-side functions
required for a single-ended, isolated offline, switch-mode power converter that uses secondary-side PWM
control. It is usable with a wide range of secondary circuits and is especially well suitable for systems where
sophisticated handling of overload conditions is required.
Secondary-side control assumes that output voltage and current measurements are interfaced directly to an
output ground-referenced PWM stage that develops the power switch command for the supply. This digital
PWM command can then be transmitted to the primary-side power switch through a simple and low-cost
isolating pulse transformer. With secondary-side control, it is much easier to monitor and control the system load
with tightly coupled analog control loops. Load-oriented features such as output current sharing and
synchronous rectification are implemented more easily.
The UCC3960 provides all the circuitry required on the primary side of a secondary–side controlled power
supply. It features a free running 60-kHz to 360-kHz oscillator that is synchronizable to the secondary-side PWM
signal and also has the ability to accept start/stop PWM commands from the isolating pulse edge transformer.
The use of an extremely small and low-cost pulse transformer allows for higher converter bandwidth. This also
eliminates the loop-gain variations due to initial accuracy and aging of an opto-coupler feedback element or the
size penalty of a gate transformer. It also includes an undervoltage lockout circuit with 2-V hysteresis, a low
current startup with active low during UVLO, a soft-start capability, a 5-V reference and a high current power
output.
In a non-typical use, the UCC3960 can accommodate an analog feedback signal through an opto-isolator where
it can operate in voltage-mode control mode with primary-side peak current limiting.
The UCC3960 and the UCC2960 are available in the 8-pin SOIC (D) and PDIP (P) packages. A 14-pin package
version is available as UCC2961 and UCC3961 that includes additional protection features such as multimode
overcurrent protection, volt-second clamp, programmable overvoltage and undervoltage sense lines, and the
self-bias regulator.
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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