July 2000

ML4863

*

High Efficiency Flyback Controller

1

BLOCK DIAGRAM

GENERAL DESCRIPTION

The ML4863 is a flyback controller designed for use in

multi-cell battery powered systems such as PDAs and

notebook computers. The flyback topology is ideal for

systems where the battery voltage can be either above or

below the output voltage, and where multiple output

voltages are required.

The ML4863 uses the output voltage as the feedback

control signal to the current mode variable frequency

flyback controller. In addition, a synchronous rectifier

control output is supplied to provide the highest possible

conversion efficiency (greater than 85% efficiency over a

1mA to 1A load range).

The ML4863 has been designed to operate with a

minimum number of external components to optimize

space and cost.

*Some Packages Are Obsolete

FEATURES

s

Variable frequency current mode control and

synchronous rectification for high efficiency

s

Minimum external components

s

Guaranteed start-up and operation over a wide input

voltage range (3.15V to 15V)

s

High frequency operation (>200kHz) minimizes the

size of the magnetics

s

Flyback topology allows multiple outputs in addition to

the regulated 5V

s

Built-in overvoltage and current limit protection

SWITCHING

CONTROL

BLANKING

CROSS-CONDUCTION

PROTECTION

VFB

I

4.5V

LDO

RECTIFIER

COMPARATOR

CURRENT

COMPARATOR

Rgm

18mV

–

+

VREF

3

SHDN

5

VCC

8

GND

6

OUT 1

7

OUT 2

2

SENSE

1

VIN

VFB

VCC

4

VFB

BIAS & UVLO

+

–

COMP

–

+

COMP

18mV

VCC

VCC

A2

A1

FEATURING

Extended Commercial

Temperature

Range

-20˚C to 70˚C

for Portable

Handheld

Equipment