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LM138 Datasheet

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
3
1
TO-220
1
2
3
TO-3
Typical Application Circuit
Copyright © 2016, Texas Instruments Incorporated
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.
1
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

No Preview Available !

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
2
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Copyright © 1998–2016, Texas Instruments Incorporated
Product Folder Links: LM138 LM338


Part Number LM138
Description 5-Amp Adjustable Regulator
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