July 2000

PRELIMINARY

ML4769

*

2 Cell, Adjustable Output Boost Regulator

with Load Disconnect

1

GENERAL DESCRIPTION

The ML4769 is a continuous conduction boost regulator

designed for DC to DC conversion in multiple cell battery

power systems. Continuous conduction allows the

regulator to maximize output current for a given inductor.

The maximum switching frequency can exceed 200kHz,

allowing the use of small, low cost inductors. The ML4769

is capable of start-up with input voltages as low as 1.8V.

The output voltage can be set anywhere between 3.0V

and 5.5V by an external resistor divider connected to the

SENSE pin.

An integrated synchronous rectifier eliminates the need

for an external Schottky diode and provides a lower

forward voltage drop, resulting in higher conversion

efficiency. In addition, low quiescent current and variable

frequency operation result in high efficiency even at light

loads. The ML4769 requires only a few external

components to build a very small regulator capable of

achieving conversion efficiencies approaching 85%.

The SHDN input allows the user to stop the regulator from

switching, and provides complete isolation of the load

* Some Packages Are Obsolete

from the battery.

BLOCK DIAGRAM

FEATURES

s

Guaranteed full load start-up and operation at

1.8V input

s

Continuous conduction mode for high output current

s

Pulse Frequency Modulation and internal synchronous

rectification for high efficiency

s

Isolates the load from the input during shutdown

s

Minimum external components

s

Low ON resistance internal switching FETs

s

Low supply current

s

Adjustable output voltage (3V to 5.5V)

VL2

5

VOUT

4

SENSE

6

+

–

SHUTDOWN

CONTROL

7

SHDN

VIN

2

2.57V

START-UP

3

GND

VL1

1

SYNCHRONOUS

RECTIFIER

CONTROL

BOOST

CONTROL

SHDN

+

–

+

–

8

PWR GND