Datasheet

LM138

LM338

www.ti.com

SNVS771C –MAY 1998–REVISED DECEMBER 2016

Product Folder Links: LM138 LM338

7 Detailed Description

7.1 Overview

The LM138 and LM338 devices are adjustable, three-terminal, positive-voltage regulators capable of supplying

more than 5 A over an output-voltage range of 1.2 V to 32 V. It requires only two external resistors to set the

output voltage. These devices feature a typical line regulation of 0.005% and typical load regulation of 0.1%. It

includes time-dependent current limiting, thermal overload protection, and safe operating area protection.

Overload protection remains functional even if the ADJUST terminal is disconnected.

The LM138 and LM338 devices are versatile in their applications, including uses in programmable output

regulation and local on-card regulation. Or, by connecting a fixed resistor between the ADJUST and OUTPUT

terminals, the LM138 and LM338 devices can function as a precision current regulators. An optional output

capacitor can be added to improve transient response. The ADJUST terminal can be bypassed to achieve very

high ripple-rejection ratios, which are difficult to achieve with standard three-terminal regulators.

7.2 Functional Block Diagram

7.3 Feature Description

7.3.1 NPN Darlington Output Drive

NPN Darlington output topology provides naturally low output impedance and an output capacitor is optional. To

support maximum current and lowest temperature, 3-V headroom is recommended (V

– V

7.3.2 Overload Block

Overcurrent and overtemperature shutdown protects the device against overload or damage from operating in

excessive heat.

7.3.3 Programmable Feedback

Op amp with 1.25-V offset input at the ADJUST terminal provides easy output voltage or current (not both)

programming. For current regulation applications, a single resistor whose resistance value is 1.25 V/IO and

power rating is greater than 1.25 V

/R must be used. For voltage regulation applications, two resistors set the

output voltage.