+

Over Temp &

Over Current

Protection

Input

Adj.

Output

1.25 V

LM317

SLVS044W – SEPTEMBER 1997 – REVISED OCTOBER 2014

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8 Detailed Description

8.1 Overview

The LM317 device is an adjustable three-terminal positive-voltage regulator capable of supplying more than 1.5

A over an output-voltage range of 1.25 V to 37 V. It requires only two external resistors to set the output voltage.

The device features a typical line regulation of 0.01% and typical load regulation of 0.1%. It includes current

limiting, thermal overload protection, and safe operating area protection. Overload protection remains functional

even if the ADJUST terminal is disconnected.

The LM317 device is versatile in its 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 LM317

device can function as a precision current regulator. 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.

8.2 Functional Block Diagram

8.3 Feature Description

8.3.1 NPN Darlington Output Drive

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

8.3.2 Overload Block

Over-current and over-temperature shutdown protects the device against overload or damage from operating in

excessive heat.

8.3.3 Programmable Feedback

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

voltage.

8

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