July 2000

PRELIMINARY

ML4770

*

2 Cell, Adjustable Output, High Current

Boost Regulator with Load Disconnect

1

GENERAL DESCRIPTION

The ML4770 is a continuous conduction mode 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 ML4770 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 ML4770 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

* Some Packages Are Obsolete

switching, and provides complete isolation of the load

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