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ML4870CS-3

High Current Boost Regulator with Load Disconnect

Micro Linear Corporation 

July 2000

PRELIMINARY

ML4870*

High Current Boost Regulator with Load Disconnect

GENERAL DESCRIPTION

The ML4870 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 ML4870

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 addtion, low quiescent current and variable

frequency operation result in high efficiency even at light

loads. The ML4870 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

from the battery.

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 5V and 3.3V output versions

*Some Packages Are Obsolete

BLOCK DIAGRAM

VIN

2

1

VL1

START-UP

6

VL2

SYNCHRONOUS

RECTIFIER

CONTROL

SHUTDOWN

CONTROL

SHDN

4

VOUT

5

+

–

BOOST

SHDN

CONTROL

2.4V

PWR GND

8

GND

3

1

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