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5-Amp Adjustable Regulator

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LM138, LM338

SNVS771C – MAY 1998 – REVISED DECEMBER 2016

LM138 and LM338 5-Amp Adjustable Regulators

1 Features

•1 Specified 7-A Peak Output Current

• Specified 5-A Output Current

• Adjustable Output Down to 1.2 V

• Specified Thermal Regulation

• Current Limit Constant With Temperature

• P + Product Enhancement Tested

• Output is Short-Circuit Protected

2 Applications

• Adjustable Power Supplies

• Constant Current Regulators

• Battery Chargers

Pin 1. Adjustment

2. Output

3. Input

Tab/Case is Output

Available Packages

TO-220

TO-3

Typical Application Circuit

3 Description

The LM138 series of adjustable 3-terminal positive

voltage regulators is capable of supplying in excess

of 5 A over a 1.2-V to 32-V output range. They are

exceptionally easy to use and require only 2 resistors

to set the output voltage. Careful circuit design has

resulted in outstanding load and line regulation,

comparable to many commercial power supplies. The

LM138 family is supplied in a standard 3-lead

transistor package.

A unique feature of the LM138 family is time-

dependent current limiting. The current limit circuitry

allows peak currents of up to 12 A to be drawn from

the regulator for short periods of time. This allows the

LM138 to be used with heavy transient loads and

speeds start-up under full-load conditions. Under

sustained loading conditions, the current limit

decreases to a safe value protecting the regulator.

Also included on the chip are thermal overload

protection and safe area protection for the power

transistor. Overload protection remains functional

even if the adjustment (ADJ) pin is accidentally

disconnected.

Normally, no capacitors are needed unless the device

is situated more than 6 inches from the input filter

capacitors in which case an input bypass is needed.

An output capacitor can be added to improve

transient response, while bypassing the adjustment

pin increases the ripple rejection of the regulator.

Besides replacing fixed regulators or discrete

designs, the LM138 is useful in a wide variety of

other applications. Because the regulator is floating

and receives only the input-to-output differential

voltage, supplies of several hundred volts can be

regulated as long as the maximum input to output

differential is not exceeded; do not short-circuit output

to ground. The part numbers in the LM138 series

which have a K suffix are packaged in a standard

steel TO-CAN package, while those with a T suffix

are packaged in a TO-220 plastic package. The

LM138 is rated for TJ = –55°C to 150°C, and the

LM338 is rated for TJ = 0°C to 125°C.

Device Information(1)

PART NUMBER

PACKAGE

BODY SIZE (NOM)

LM138

TO-CAN (2)

25.40 mm × 38.94 mm

LM338

TO-220 (3)

TO-CAN (2)

10.16 mm × 14.986 mm

25.40 mm × 38.94 mm

(1) For all available packages, see the orderable addendum at

the end of the data sheet.

An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications,

intellectual property matters and other important disclaimers. PRODUCTION DATA.

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LM138 Datasheet Preview

LM138 Datasheet

5-Amp Adjustable Regulator

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LM138, LM338

SNVS771C – MAY 1998 – REVISED DECEMBER 2016

www.ti.com

Table of Contents

1 Features .................................................................. 1

2 Applications ........................................................... 1

3 Description ............................................................. 1

4 Revision History..................................................... 2

5 Pin Configuration and Functions ......................... 3

6 Specifications......................................................... 3

6.1 Absolute Maximum Ratings ...................................... 3

6.2 Recommended Operating Conditions....................... 3

6.3 Thermal Information .................................................. 4

6.4 Electrical Characteristics: LM138.............................. 4

6.5 Electrical Characteristics: LM338.............................. 5

6.6 Typical Characteristics .............................................. 6

7 Detailed Description .............................................. 9

7.1 Overview ................................................................... 9

7.2 Functional Block Diagram ......................................... 9

7.3 Feature Description................................................... 9

7.4 Device Functional Modes........................................ 10

8 Application and Implementation ........................ 11

8.1 Application Information............................................ 11

8.2 Typical Applications ................................................ 12

8.3 System Examples ................................................... 17

9 Power Supply Recommendations...................... 23

10 Layout................................................................... 23

10.1 Layout Guidelines ................................................. 23

10.2 Layout Example .................................................... 23

11 Device and Documentation Support ................. 24

11.1 Receiving Notification of Documentation Updates 24

11.2 Related Links ........................................................ 24

11.3 Community Resources.......................................... 24

11.4 Trademarks ........................................................... 24

11.5 Electrostatic Discharge Caution ............................ 24

11.6 Glossary ................................................................ 24

12 Mechanical, Packaging, and Orderable

Information ........................................................... 24

4 Revision History

NOTE: Page numbers for previous revisions may differ from page numbers in the current version.

Changes from Revision B (April 2013) to Revision C

Page

• Added Device Information table, Pin Configuration and Functions section, Specifications section, Recommended

Operating Conditions table, Thermal Information table, Detailed Description section, Application and Implementation

section, Power Supply Recommendations section, Layout section, Device and Documentation Support section, and

Mechanical, Packaging, and Orderable Information section .................................................................................................. 1

• Deleted RETS138K military specification reference from Absolute Maximum Ratings table................................................. 3

• Changed Junction to Ambient, RθJA, value in Thermal Information table From: 50°C/W To: 22.9°C/W (NDE) ..................... 4

• Changed Junction to Case, RθJC(top), value in Thermal Information table From: 4°C/W To: 15.7°C/W (NDE) ....................... 4

Changes from Revision A (April 2013) to Revision B

Page

• Changed layout of National Semiconductor Data Sheet to TI format .................................................................................... 1

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LM138 Datasheet

5-Amp Adjustable Regulator

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