LM78S40

Universal Switching Regulator Subsystem

General Description

The LM78S40 is a monolithic regulator subsystem consisting

of all the active building blocks necessary for switching regu-

lator systems. The device consists of a temperature com-

pensated voltage reference, a duty-cycle controllable oscilla-

tor with an active current limit circuit, an error amplifier, high

current, high voltage output switch, a power diode and an

uncommitted operational amplifier. The device can drive ex-

ternal NPN or PNP transistors when currents in excess of

1.5A or voltages in excess of 40V are required. The device

can be used for step-down, step-up or inverting switching

regulators as well as for series pass regulators. It features

wide supply voltage range, low standby power dissipation,

high efficiency and low drift. It is useful for any stand-alone,

low part count switching system and works extremely well in

battery operated systems.

Features

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Step-up, step-down or inverting switching regulators

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Output adjustable from 1.25V to 40V

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Peak currents to 1.5A without external transistors

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Operation from 2.5V to 40V input

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Low standby current drain

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80 dB line and load regulation

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High gain, high current, independent op amp

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Pulse width modulation with no double pulsing

Block and Connection Diagrams

DS010057-2

16-Lead DIP

DS010057-1

Top View

April 1998

© 1998 National Semiconductor Corporation

DS010057

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