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

Datasheet	Packaging	Samples & Pricing	Reliability	Application Notes	Knowledge Base

Features

•	Output voltage specified over temperature
•	Excellent load regulation
•	Guaranteed 1A output current
•	Requires only one external component
•	Built-in protection against excess temperature
•	Short circuit protected

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.

Applications

•	Laptop/Desktop Computers
•	Logic Systems

Typical Application

click for larger image

Parametric Table expand

Parametric Table collapse

Output Current 1000 mA

Output Min 3.3 Volt

Input Max Voltage 7.5 Volt

Dropout Voltage 0.31 Volt

Adjustable Output No

Quiescent Current 0.11 mA

Output Current 1000 mA

Output Min 3.3 Volt

Input Max Voltage 7.5 Volt

Dropout Voltage 0.31 Volt

Adjustable Output No

Quiescent Current 0.11 mA

On/Off Pin No

Error Flag No

RegType LDO

Temperature Min -40 deg C

Temperature Max 125 deg C

Output Voltage 3.3 Volt

Output Max 3.3 Volt

View Using Catalog

Typical Performance

click for larger image

Also Recommended

LM2677	Higher Efficiency & Better Transient Response
LM2678	Higher Efficiency & Better Transient Response
LP38690	Lower Supplu Current , Stable With Ceramic Capacitor
LP38692	Lower Quiescent Current, Stable With Ceramic Output Capacitors & Enable Pin
LP3872	Improved Output Current, Fast Response, Lower Supply Current

Additional Resources

Application Notes (see below)

Connection Diagram

click for larger image

Datasheet

RoHS Compliance Information	Size in Kbytes	Date
LM3940 1A Low Dropout Regulator for 5V to 3.3V Conversion	328 Kbytes	19-Jul-07	Download
LM3940 1A Low Dropout Regulator for 5V to 3.3V Conversion (Japanese)	361 Kbytes

If you have trouble printing or viewing PDF file(s), see Printing Problems.

Package Availability, Models, Samples & Pricing

Part Number

Package

Factory Lead Time

Models

Samples &
Electronic
Orders

Budgetary Pricing

Std
Pack
Size

Package
Marking
Format

Type

Pins

Spec.

MSL
Rating

Peak
Reflow

RoHS
Report

CAD
Symbols

Weeks

Qty

$US each

LM3940LD-3.3

LLP

STD

NOPB

235

260

RoHS

Download

Lifetime buy

N/A

1K+

$0.78

reel
of
1000

NS
UZXYTT
L00013B

8 weeks

1000

LM3940LDX-3.3

LLP

STD

235

RoHS

Download

Lifetime buy

N/A

1K+

$0.78

reel
of
4500

NS
UZXYTT
L00013B

12 weeks

7500

LM3940IMP-3.3

SOT-223

STD

NOPB

260

RoHS

Download

Full production

N/A

1K+

$0.70

reel
of
1000

XYTT
L52B

8 weeks

2000

LM3940IMPX-3.3

SOT-223

STD

NOPB

260

RoHS

Download

Full production

N/A

1K+

$0.70

reel
of
2000

XYTT
L52B

8 weeks

2500

LM3940IT-3.3

TO-220

STD

NOPB

RoHS

Download

Full production

N/A

1K+

$0.83

rail
of
45

NSUZXYTTE#
LM3940IT
-3.3 P+

8 weeks

1000

LM3940IS-3.3

TO-263

STD

NOPB

235

245

RoHS

Download

Full production

N/A

1K+

$0.86

rail
of
45

NSUZXYTTE#
LM3940IS
-3.3 P+

8 weeks

2000

LM3940ISX-3.3

TO-263

STD

NOPB

235

245

RoHS

Download

Full production

N/A

1K+

$0.86

reel
of
500

NSUZXYTTE#
LM3940IS
-3.3 P+

8 weeks

2500

Obsolete Versions

Obsolete Part	Alternate Part or Supplier	Source	Last Time Buy Date
LM3940J-3.3-MPR	NONE	NONE	01 Dec 2004
LM3940J-3.3-QML	NONE	NONE	02 Jun 2004
LM3940J-3.3-SCD	NONE	NONE	01 Dec 2004
LM3940LD-3.3	NONE	NATIONAL SEMICONDUCTOR	01 Dec 2009
LM3940LDX-3.3	NONE	NATIONAL SEMICONDUCTOR	01 Dec 2009
LM3940WG3.3-MPR	NONE	NONE	01 Dec 2004
LM3940WG3.3-QML	NONE	NONE	02 Jun 2004
LM3940WG3.3-SCD	NONE	NONE	01 Dec 2004

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.

Reliability Metrics

Part Number	Process	EFR Reject	EFR Sample Size	PPM	LTA Rejects	LTA Device Hours	FITS	MTTF (Hours)
LM3940IMP-3.3	SLM	0	42786	0	0	3352500	2	951281028
LM3940IMPX-3.3	SLM	0	42786	0	0	3352500	2	951281028
LM3940IS-3.3	SLM	0	42786	0	0	3352500	2	951281028
LM3940ISX-3.3	SLM	0	42786	0	0	3352500	2	951281028
LM3940IT-3.3	SLM	0	42786	0	0	3352500	2	951281028
LM3940LD-3.3	SLM	0	42786	0	0	3352500	2	951281028
LM3940LDX-3.3	SLM	0	42786	0	0	3352500	2	951281028

Note: The Early Failure Rates (EFR) were calculated as point estimate PPM based on rejects and sample size for EFR. The Long Term Failure Rates were calculated at 60% confidence using the Arrhenius equation at 0.7eV activation energy and derating the assumed stress temperature of 150°C to an application temperature of 55°C.

For more information on Reliability Metrics, please click here.

Application Notes

Title	Size in Kbytes	Date
AN-1061: Application Note 1061 Power Conversion in Line-Powered Equipment	162 Kbytes	1-Oct-02	Download
AN-1061 (Japanese): Application Note 1061 Power Conversion in Line-Powered Equipment	215 Kbytes

If you have trouble printing or viewing PDF file(s), see Printing Problems.

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[Information as of 3-Jul-2009]