LM3940IS

Part: LM3940 from Texas Instruments

Type: Low-Dropout Regulator

Key Specs:

• Input Voltage Range: 4.5 V to 5.5 V
• Output Current: 1 A
• Output Voltage: 3.3 V

Features:

• Output Voltage Specified over Temperature
• Excellent Load Regulation
• Requires only One External Component
• Built-in Protection against Excess Temperature
• Short-Circuit Protected

Applications:

• Laptop and Desktop Computers
• Logic Systems

Package:

• 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 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

• Laptop and Desktop Computers
• • Logic Systems

1

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)

Simplified Schematic

*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.

1 Features.................................................................. 1 2 Applications ........................................................... 1 3 Description ............................................................. 1 4 Revision History..................................................... 2 5 Pin Configuration and Functions......................... 3 6 Specifications......................................................... 4 6.1 Absolute Maximum Ratings ...................................... 4 6.2 ESD Ratings.............................................................. 4 6.3 Recommended Operating Conditions....................... 4 6.4 Thermal Information.................................................. 4 6.5 Electrical Characteristics........................................... 5 6.6 Typical Characteristics .............................................. 6 7 Detailed Description .............................................. 8 7.1 Overview ................................................................... 8 7.2 Functional Block Diagram ......................................... 8 7.3 Feature Description................................................... 8 7.4 Device Functional Modes.......................................... 8

2

3-Pin DDPAK/TO-263 Package Front View

Pin Functions

• NAME
• IN
• GND
• OUT

Over operating free-air temperature range, VIN = 5 V, IOUT = 1 A, COUT = 33 μF (unless otherwise noted). Limits apply for T^J = 25°C, unless otherwise specified in the Test Conditions column.(1)

(2) 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 VIN = 5 V.

over operating free-air temperature range (unless otherwise noted)(1)

(1) Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings only, which do not imply functional operation of the device at these or any other conditions beyond those indicated under Recommended Operating Conditions. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.

(2) The maximum allowable power dissipation is a function of the maximum junction temperature, T^J , the junction-to-ambient thermal resistance, RθJA, and the ambient temperature, TA. Exceeding the maximum allowable power dissipation will cause excessive die temperature, and the regulator will go into thermal shutdown. The value of RθJA (for devices in still air with no heatsink) is 23.3°C/W for the TO-220 package, 40.9°C/W for the DDPAK/TO-263 package, and 59.3°C/W for the SOT-223 package. The effective value of RθJA can be reduced by using a heatsink (see Heatsinking for specific information on heatsinking).

over operating free-air temperature range (unless otherwise noted)

(1) For more information about traditional and new thermal metrics, see the IC Package Thermal Metrics application report, SPRA953.

6.5 Electrical Characteristics

Over operating free-air temperature range, VIN = 5 V, IOUT = 1 A, COUT = 33 μF (unless otherwise noted). Limits apply for T^J = 25°C, unless otherwise specified in the Test Conditions column.(1)

(2) 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 VIN = 5 V.