GENERAL DESCRIPTION

The ML4871 is a continuous conduction boost regulator

designed for DC to DC conversion in multiple cell battery

powered 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 ML4871

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

and is available in 5V and 3.3V output versions with an

output voltage accuracy of ±3%.

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 battery current and variable

frequency operation result in high efficiency even at light

loads. The ML4871 requires only one inductor and two

capacitors to build a very small regulator circuit capable

of achieving conversion efficiencies approaching 90%.

The circuit also contains a RESET output which goes low

when the DETECT input drops below 1.25V.

BLOCK DIAGRAM

July 2000

ML4871

High Current Boost Regulator

1

FEATURES

s

Guaranteed full load start-up and operation

at 1.8V Input

s

Continuous conduction mode for high output current

s

Very low supply current (20µA output referenced) for

Micropower operation

s

Pulse Frequency Modulation and Internal Synchronous

Rectification for high efficiency

s

Maximum switching frequency > 200kHz

s

Minimum external components

s

Low ON resistance internal switching FETs

s

5V and 3.3V output versions

VL2

5

VOUT

6

+

–

VIN

2

1.25V

START-UP

3

GND

VL1

1

DETECT

4

SYNCHRONOUS

RECTIFIER

CONTROL

BOOST

CONTROL

+

–

+

–

8

PWR GND

RESET

VREF

+

–

COMP

7

FEATURING

Extended Commercial

Temperature

Range

-20˚C to 70˚C

for Portable

Handheld

Equipment