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October 2002

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1V TO 6V INPUT GUARANTEES START-UP

UNDER LOAD

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MAXIMUM OUTPUT CURRENT OF 300mA

(778 OR 779 ADJUSTED TO 3V)

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LOAD FULLY DISCONNECTED IN

SHUTDOWN

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TYPICAL EFFICIENCY OF 82%

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INTERNAL 1A POWER SWITCH AND

SYNCHRONOUS RECTIFIER

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ADJUSTABLE CURRENT LIMIT ALLOWS

LOW-COST INDUCTORS

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SUPPLY CURRENT OF 270µA (NO LOAD)

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SHUTDOWN SUPPLY CURRENT 20µA

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PACKAGE AVAILABLE: DIP-8 AND SO-8

DESCRIPTION

The ST777/778/779 are dc-dc converters that

step-up from low voltage inputs requiring only

three external components, an inductor (typically

22µH) and two capacitors. The device include a

Sinchronous Rectifier that eliminates the need for

an external catch diode, and allows regulation

even when the input is greater than the output.

Unlike others step-up DC-DC converters the

ST777/778/779’s Sinchronous Rectifier turns off in

the shutdown mode, fully disconnecting the output

from the source. This eliminates the current drain

associated with conventional step-up converters

when off or in shutdown. Supply current is 270µA

under no load and only 20µA in stand by mode.

ST777/778/779

LOW VOLTAGE INPUT, 3-3.3V/5V/ADJUSTABLE OUTPUT

DC-DC CONVERTER WITH SYNCHRONOUS RECTIFIER

22µH

100µF

100µF

IN

OUT

PGND

SEL

AGND

1

2

3

4

5

6

7

8

SHDN

1.25V

VREF

SHUTDOWN

CONTROL

DELAY

TIMER

DELAY

TIMER

SWITCH

DRIVER

ACTIVE RECTIFIER

RECTIFIER

CONTROL

1: N

SCHEMATIC DIAGRAM

SO-8

DIP-8