July 2000

ML4865

High Voltage High Current Boost Regulator

1

GENERAL DESCRIPTION

The ML4865 is a high voltage, 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 ML4865 is capable of start-up with

input voltages as low as 1.8V and generates a 12V output

with output voltage accuracy of ±4%.

Unlike most boost regulators, the ML4865 isolates the

load from the battery when the SHDN pin is high. 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 ML4865 requires only one inductor and two

capacitors to build a very small regulator circuit capable

of achieving conversion efficiencies approaching 90%.

BLOCK DIAGRAM

FEATURES

s Guaranteed full load start-up and operation at 1.8V

input

s Continuous conduction mode for high output current

s Very low quiescent current

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 Fixed 12V output can be adjusted to lower output

voltages

VL2

8

VOUT

1

SENSE

6

+

–

SHUTDOWN

CONTROL

7

SHDN

VIN

3

2.42V

START-UP

2

GND

VL1

4

SYNCHRONOUS

RECTIFIER

CONTROL

BOOST

CONTROL

SHDN

+

–

+

–

5

PWR GND

FEEDBACK

CONTROL