May 1997

ML4828

*

BiCMOS Phase Modulation/Soft Switching Controller

1

GENERAL DESCRIPTION

The ML4828 is a complete BiCMOS phase modulation

control IC suitable for full bridge soft switching converters.

Unlike conventional PWM circuits, the phase modulation

technique allows for zero voltage switching (ZVS)

transitions and square wave drive across the transformer.

The IC modulates the phases of the two sides of the bridge

to control output power.

The ML4828 can be operated in either voltage or current

mode. Both cycle-by-cycle current limit, integrating fault

detection, and soft start reset are provided. The under-

voltage lockout circuit features a 1.5V hysteresis with a

low starting current to allow off-line start up with a bleed

resistor. A shutdown function powers down the IC, putting

it into a low quiescent state.

The circuit can be operated at frequencies up to 1MHz.

The ML4828 contains four high current CMOS outputs

which feature high slew rate with low cross conduction.

*Some Packages Are End Of Life

BLOCK DIAGRAM

FEATURES

s

5V BiCMOS for low power and high frequency

(1MHz) operation

s

Full bridge phase modulation zero voltage switching

circuit with independent programmable delay times

s

Current or voltage mode operation capability

s

Cycle-by-cycle current limiting with integrating fault

detection and restart delay

s

Can be externally synchronized

s

Four 3

Ω CMOS output drivers

s

Under-voltage lockout circuit with 1.5V hysteresis

8

–

+

DELAY B

DRIVER

DRIVER

DRIVER

+

–

2.5V REF

11

16 A2

15 B1

13 B2

–

+

ISS

IRST

FAULT

LOGIC

Q

Q

S

R

2

17

GND

1

5

EAO

RAMP

SS

RST

SDN

DRIVER

DELAY A

A1

18

ΦMOD

12

20

S

Q

R

Q

7

1.25V

2.5V

19

UVLO

10

9

EA+

EA–

–

+

OSC

T

Q

Q

6

4

3

14

ERROR

AMP

1V