NSC LM3940WG3.3-QML Datasheet

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

n Laptop/Desktop Computers
n Logic Systems

Typical Application

DS012080-1

*

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

**

See Application Hints.

May 1999

LM3940 1A Low Dropout Regulator for 5V to 3.3V Conversion

© 1999 National Semiconductor Corporation DS012080 www.national.com

Connection Diagram/Ordering Information

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3-Lead TO-220 Package

(Front View)

Order Part Number LM3940IT-3.3

NSC Drawing Number TO3B

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3-Lead TO-263 Package

(Front View)

Order Part Number LM3940IS-3.3

NSC Drawing Number TS3B

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3-Lead SOT-223

(Front View)

Order Part Number LM3940IMP-3.3

Package Marked L52B

NSC Drawing Number MA04A

DS012080-27

16-Lead Ceramic Dual-in-Line Package

(Top View)

Order Part Number LM3940J-3.3-QML

5962-9688401QEA

NSC Drawing Number J16A

DS012080-28

16-Lead Ceramic Surface-Mount Package

(Top View)

Order Part Number LM3940WG-3.3-QML

5962-9688401QXA

NSC Drawing Number WG16A

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Absolute Maximum Ratings (Note 1)

If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.

Storage Temperature Range −65˚C to +150˚C

Operating Junction Temperature Range −40˚C to +125˚C
Lead Temperature (Soldering, 5 seconds) 260˚C
Power Dissipation (Note 2) Internally Limited
Input Supply Voltage 7.5V
ESD Rating (Note 3) 2 kV

Electrical Characteristics

Limits in standard typeface are for T

J

=

25˚C, and limits in boldface type apply over the full operating temperature range. Un-

less otherwise specified: V

IN

=

5V, I

L

=

1A, C

OUT

=

33 µF.

Symbol Parameter Conditions Typical LM3940 (Note 4) Units

min max

V

O

Output Voltage 5 mA ≤ IL≤ 1A 3.3 3.20 3.40 V

3.13 3.47

Line Regulation I

L

=

5mA

20

40 mV

4.5V ≤ V

O

≤ 5.5V

Load Regulation 50 mA ≤ IL≤ 1A

35

50

80

Z

O

Output Impedance IL(DC)=100 mA

I

L

(AC)=20 mA (rms) 35 mΩ

f=120 Hz

I

Q

Quiescent Current 4.5V ≤ VIN≤ 5.5V 10 15 mA

I

L

=

5mA 20

V

IN

=

5V 110 200

I

L

=

1A 250

e

n

Output Noise Voltage BW=10 Hz–100 kHz 150 µV (rms)

I

L

=

5mA

V

O−VIN

Dropout Voltage I

L

=

1A 0.5 0.8 V

(Note 5) 1.0

I

L

=

100 mA 110 150 mV

200

I

L

(SC) Short Circuit Current R

L

=

0 1.7 1.2 A

Note 1: Absolute maximum ratings indicate limits beyond which damage to the component may occur. Electrical specifications do not apply when operating the de­vice outside of its rated operating conditions.

Note 2: The maximum allowable power dissipation is a function of the maximum junction temperature, T

J

, the junction-to-ambient thermal resistance, θ

J−A

, and the

ambient temperature,T

A

. Exceeding themaximumallowablepower dissipation will cause excessive die temperature, and the regulator will go into thermal shutdown.

The value of θ

J−A

(for devices in still air with no heatsink) is 60˚C/W for the TO-220 package, 80˚C/W for the TO-263 package, and 174˚C/W for the SOT-223 package.

The effective value of θ

J−A

can be reduced by using a heatsink (see Application Hints for specific information on heatsinking).

Note 3: ESD rating is based on the human body model: 100 pF discharged through 1.5 kΩ.
Note 4: All limits guaranteed for T

J

=

25˚C are 100%tested and are used to calculate Outgoing Quality Levels. All limits at temperature extremes are guaranteed

via correlation using standard Statistical Quality Control (SQC) methods.
Note 5: Dropout voltage is defined as the input-output differential voltage where the regulator output drops to a value that is 100 mV below the value that is measured

at V

IN

=

5V.

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Typical Performance Characteristics

Dropout Voltage

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Dropout Voltage
vs Temperature

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Output Voltage
vs Temperature

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Quiescent Current
vs Temperature

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Quiescent Current vs V

IN

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Quiescent Current vs Load

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Line Transient Response

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Load Transient Response

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Ripple Rejection

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Low Voltage Behavior

DS012080-22

Output Impedance

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Peak Output Current

DS012080-24

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