GENERAL DESCRIPTION

The ML4823 High Frequency PWM Controller is an IC controller optimized for use in Switch Mode Power Supply designs running at frequencies to 1MHz. Propagation delays are minimal through the comparators and logic for reliable high frequency operation while slew rate and bandwidth are maximized on the error amplifier. This controller is designed for single-ended applications using voltage or current mode and provides for input voltage feed forward.

A 1V threshold current limit comparator provides cycle by-cycle current limit and exceeding a 1.4V threshold initiates a soft-start cycle. The soft start pin doubles as a maximum duty cycle clamp. All logic is fully latched to provide jitter-free operation and prevent multiple pulsing. An under-voltage lockout circuit with 800mV of hysteresis assures low startup current and drives the outputs low during fault conditions.

This controller is an improved second source for the UC3823 controller; however, the ML4823 includes features not found on the 3823. These features are set in italics.

FEATURES

■ Practical operation at switching frequencies to 1.0MHz

■ High current (2A peak) totem pole output

■ Wide bandwidth error amplifier

■ Fully latched logic with double pulse suppression

■ Pulse-by-pulse current limiting

■ Soft start and max. duty cycle control

■ Under voltage lockout with hysteresis

■ 5.1V trimmed bandgap reference

■ Low start-up current (1.1mA)

■ Pin compatible improved replacement for UC3823

■ Fast shut down path from current limit to output

■ Soft start latch ensures full soft start cycle

■ Outputs pull low for undervoltage lockout