SNVS114G May   1999  – February 2015 LM3940

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
  6. 6 Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 ESD Ratings
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information
    5. 6.5 Electrical Characteristics
    6. 6.6 Typical Characteristics
  7. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Output Voltage Accuracy
      2. 7.3.2 Short-Circuit Protection
      3. 7.3.3 Thermal Protection
    4. 7.4 Device Functional Modes
      1. 7.4.1 Operation with VIN = 5 V
  8. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
        1. 8.2.2.1 External Capacitors
          1. 8.2.2.1.1 Minimum Capacitance
          2. 8.2.2.1.2 ESR Limits
      3. 8.2.3 Application Curves
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
    3. 10.3 Heatsinking
      1. 10.3.1 Heatsinking TO-220 Package Parts
      2. 10.3.2 Heatsinking DDPAK/TO-263 and SOT-223 Package Parts
  11. 11Device and Documentation Support
    1. 11.1 Documentation Support
      1. 11.1.1 Related Documentation
    2. 11.2 Receiving Notification of Documentation Updates
    3. 11.3 Community Resources
    4. 11.4 Trademarks
    5. 11.5 Electrostatic Discharge Caution
    6. 11.6 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information

1 Features

  • Input Voltage Range: 4.5 V to 5.5 V
  • Output Voltage Specified over Temperature
  • Excellent Load Regulation
  • Specified 1-A Output Current
  • Requires only One External Component
  • Built-in Protection against Excess Temperature
  • Short-Circuit Protected

2 Applications

  • Laptop and Desktop Computers
  • Logic Systems

3 Description

The LM3940 is a 1-A low-dropout regulator designed to provide 3.3 V from a 5-V supply.

The LM3940 is ideally suited for systems which contain both 5-V and 3.3-V logic, with prime power provided from a 5-V bus.

Because the LM3940 is a true low dropout regulator, it can hold its 3.3-V output in regulation with input voltages as low as 4.5 V.

The TO-220 package of the LM3940 means that in most applications the full 1 A of load current can be delivered without using an additional heatsink.

The surface mount DDPAK/TO-263 package uses minimum board space, and gives excellent power dissipation capability when soldered to a copper plane on the PC board.

Device Information(1)

PART NUMBER PACKAGE BODY SIZE (NOM)
LM3940 SOT-223 (4) 6.50 mm x 3.50 mm
DDPAK/TO-263 (3) 10.18 mm x 8.41 mm
TO-220 (3) 14.986 mm x 10.16 mm
  1. For all available packages, see the orderable addendum at the end of the datasheet.

Simplified Schematic

LM3940 1208001.png
*Required if regulator is located more than 1 inch from the power supply filter capacitor or if battery power is used.
**See Application and Implementation.