UCC3960

ą 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...