May 1997

ML4823

*

High Frequency Power Supply Controller

FEATURES

s

Practical operation at switching frequencies to 1.0MHz

s

High current (2A peak) totem pole output

s

Wide bandwidth error amplifier

s

Fully latched logic with double pulse suppression

s

Pulse-by-pulse current limiting

s

Soft start and max. duty cycle control

s

Under voltage lockout with hysteresis

s

5.1V trimmed bandgap reference

s

Low start-up current (1.1mA)

s

Pin compatible improved replacement for UC3823

s

Fast shut down path from current limit to output

s

Soft start latch ensures full soft start cycle

s

Outputs pull low for undervoltage lockout

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

*Some Packages Are Obsolete

italics.

5

6

OSC

4

7

3

RAMP

E/A OUT

COMP

+

–

+

1.25V

S

R

Q

13

14

12

ERROR

AMP

+

–

2

1

NI

INV

OUTPUT

POWER GND

CLOCK OUT

8

SOFT START

V+

+

–

1V

11

9

+

–

1.4V

–

+

S

R

Q

4V

5.1V

+

–

16

+

–

ENABLE

15

UNDER

VOLTAGE

LOCKOUT

9V

10

SIGNAL GND

INTERNAL

BIAS

1