Datasheet

OUT REF ADJ

R 2

V = V 1+ + I R 2

R 2

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ç ÷

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LM138

LM338

www.ti.com

SNVS771C –MAY 1998–REVISED DECEMBER 2016

Product Folder Links: LM138 LM338

8 Application and Implementation

NOTE

Information in the following applications sections is not part of the TI component

specification, and TI does not warrant its accuracy or completeness. TI’s customers are

responsible for determining suitability of components for their purposes. Customers should

validate and test their design implementation to confirm system functionality.

8.1 Application Information

In operation, the LM138 develops a nominal 1.25-V reference voltage (V

REF

) between the output and adjustment

terminal. The reference voltage is impressed across program resistor R

and, since the voltage is constant, a

constant current I

then flows through the output set resistor R

, giving an output voltage calculated with

Equation 1.

(1)

Figure 15. Typical Application Circuit

Because the 50-µA current from the adjustment terminal represents an error term, the LM138 was designed to

minimize I

ADJ

and make it very constant with line and load changes. To do this, all quiescent operating current is

returned to the output establishing a minimum load current requirement. If there is insufficient load on the output,

the output rises.