GENERAL DESCRIPTION

The ML4825 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 to work in either voltage or current mode and provides for input voltage feed forward.

A 1V threshold current limit comparator provides cycle by-cycle current limit while exceeding a 1.4V threshold initiates a soft-start cycle. The soft start pin doubles as a maximum duty cycle clamp. An under-voltage lockout circuit with 800mV of hysteresis assures low startup current and drives the outputs low.

This controller is similar in architecture and performance to the UC1825 controller, however the ML4825 includes many features not found on the 1825. These features are set in Italics.

FEATURES

■ Practical operation at switching frequencies to 1.0MHz

■ High current (2A peak) dual totem pole outputs

■ Wide bandwidth error amplifier

■ Fully latched logic with double pulse suppression

■ Pulse-by-pulse current limiting

■ Soft start and maximum duty cycle control

■ Under voltage lockout with hysteresis

■ Precision trimmed 5.1V bandgap reference

■ Pin compatible improved replacement for UC1825

■ Fast shut down path from current limit to outputs

■ Outputs preset to known condition after under voltage lockout

■ Soft start latch ensures full soft start cycle

■ Outputs pull low for undervotage lockout