1FEATURES
· Frequency Foldback Reduces Operating
Frequency Under Fault Conditions
· Accurate Programmable Volt-Second Clamp
· Programmable Maximum Duty Cycle Clamp
· Oscillator Synchronization
· Overcurrent Protection
· Shutdown With Full Soft Start
· Wide Gain Bandwidth Amplifier (GBW > 2.5
MHz)
· Current Mode Operation
· Precision 5-V Reference

DESCRIPTION
The UCC3884 is a high performance current mode
PWM controller intended for single ended switch
mode power supplies. The chip implements a frequency foldback scheme that decreases the
oscillator frequency as the output voltage falls below
a programmed value. This technique decreases the
average output current sourced into a low impedance
load which can occur during an output short circuit or
overload condition. Excessive short circuit current is
more prevalent in high frequency converters where
the propagation delay and switch turn-off time forces
a minimum attainable duty cycle. An accurate
volt-second clamp limits the duty cycle during line or
load transient conditions which could otherwise
saturate the transformer. The volt-second clamp may
also be used with an external overvoltage protection
circuit to handle fault conditions such as current
sense disconnect or current transformer saturation.
The frequency foldback, volt-second clamp,
cycle-by-cycle current limit, and overcurrent shutdown
provide a rich set of protection features for use in
peak current-mode pulse width modulators.