UCC2960, UCC3960

PRIMARY SIDE STARTUP CONTROLLER

SLUS430A – APRIL 1999 – REVISED DECEMBER 2000

1

POST OFFICE BOX 655303

Control

a Pulse-Edge-Transformer

Duty-Cycle Clamping

Frequency

Source)

typical operating circuit

description

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.

Copyright

© 2000, Texas Instruments Incorporated

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.

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.

2

1

3

8

7

4

5

6

FEED

BACK

SOFT

START

FREQ

SET

GND

CS

OUT

REF

VDD

RT

SS

FB

VIN

UCC3960

Figure 1

UDG–99010

X