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LT1085IM-TR

7.5A, 5A, 3A Low Dropout Positive Adjustable Regulators

Linear Technology 

BLOCK DIAGRAM

LT1083/LT1084/LT1085

VIN

THERMAL

LIMIT

VADJ

VOUT

1083/4/5 ADJ BD

APPLICATIONS INFORMATION

The LT1083 family of 3-terminal adjustable regulators is

easy to use and has all the protection features that are

expected in high performance voltage regulators. They are

short-circuit protected, and have safe area protection as

well as thermal shutdown to turn off the regulator should

the junction temperature exceed about 165°C.

These regulators are pin compatible with older 3-terminal

adjustable devices, offer lower dropout voltage and more

precise reference tolerance. Further, the reference stability

with temperature is improved over older types of regula-

tors. The only circuit difference between using the LT1083

family and older regulators is that this new family requires

an output capacitor for stability.

Stability

The circuit design used in the LT1083 family requires the

use of an output capacitor as part of the device frequency

compensation. For all operating conditions, the addition of

a 150μF aluminium electrolytic or a 22μF solid tantalum

on the output will ensure stability. Normally, capacitors

much smaller than this can be used with the LT1083. Many

different types of capacitors with widely varying charac-

teristics are available. These capacitors differ in capacitor

tolerance (sometimes ranging up to ±100%), equivalent

series resistance, and capacitance temperature coefficient.

The 150μF or 22μF values given will ensure stability.

When the adjustment terminal is bypassed to improve the

ripple rejection, the requirement for an output capacitor

increases. The value of 22μF tantalum or 150μF aluminum

covers all cases of bypassing the adjustment terminal.

Without bypassing the adjustment terminal, smaller

capacitors can be used with equally good results and the

table below shows approximately what size capacitors are

needed to ensure stability.

Recommended Capacitor Values

INPUT

OUTPUT

10μF

10μF Tantalum, 50μF Aluminum

10μF

22μF Tantalum, 150μF Aluminum

ADJUSTMENT

None

20μF

108345fg

9

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