1

May 1997

ML4825

*

High Frequency Power Supply Controller

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.

*Some Packages Are Obsolete or End Of Life

+

+

–

OUT A

E/A OUT

INV

SS

1.4V

1V

9

µA

V+

1V

R

POWER GND

P

4V

R

TF.F.

OSC

S

UNDER

VOLTAGE

LOCKOUT

INTERNAL

BIAS

Q

ENABLE

9V

Q

Q

C

Q

S

RAMP

CLOCK OUT

OUT B

PWR GND

SIGNAL GND

NI

5

6

7

4

13

11

14

10

15

12

3

2

1

9

8

+

–

+

–

–

+

–

+

–

+

+

–

16

COMP

ERROR

AMP

1.25V

FEATURES

s

Practical operation at switching frequencies to 1.0MHz

s

High current (2A peak) dual totem pole outputs

s

Wide bandwidth error amplifier

s

Fully latched logic with double pulse suppression

s

Pulse-by-pulse current limiting

s

Soft start and maximum duty cycle control

s

Under voltage lockout with hysteresis

s

Precision trimmed 5.1V bandgap reference

s

Pin compatible improved replacement for UC1825

s

Fast shut down path from current limit to outputs

s

Outputs preset to known condition after under voltage

lockout

s

Soft start latch ensures full soft start cycle

s

Outputs pull low for undervotage lockout