LM3940

1A Low Dropout Regulator for 5V to 3.3V Conversion

General Description

The LM3940 is a 1A low dropout regulator designed to

provide 3.3V from a 5V supply.

The LM3940 is ideally suited for systems which contain both

5V and 3.3V logic, with prime power provided from a 5V bus.

Because the LM3940 is a true low dropout regulator, it can

hold its 3.3V output in regulation with input voltages as low

as 4.5V.

The T0-220 package of the LM3940 means that in most

applications the full 1A of load current can be delivered

without using an additional heatsink.

The surface mount TO-263 package uses minimum board

space, and gives excellent power dissipation capability when

soldered to a copper plane on the PC board.

Features

n

Output voltage specified over temperature

n

Excellent load regulation

n

Guaranteed 1A output current

n

Requires only one external component

n

Built-in protection against excess temperature

n

Short circuit protected

Applications

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Laptop/Desktop Computers

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Logic Systems

Typical Application

01208001

*Required if regulator is located more than 1" from the power supply filter capacitor or if battery power is used.

**See Application Hints.

Connection Diagram/Ordering Information

01208002

3-Lead TO-220 Package

(Front View)

Order Part Number LM3940IT-3.3

NSC Drawing Number TO3B

01208003

3-Lead TO-263 Package

(Front View)

Order Part Number LM3940IS-3.3

NSC Drawing Number TS3B

01208010

3-Lead SOT-223

(Front View)

Order Part Number LM3940IMP-3.3

Package Marked L52B

NSC Drawing Number MP04A

January 2003

© 2003 National Semiconductor Corporation

DS012080

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