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LT1083/LT1084/LT1085

108345fe

BLOCK DIAGRAM

APPLICATIONS INFORMATION

The LT1083 family of three-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 three-

terminal adjustable devices, offer lower dropout voltage

and more precise reference tolerance. Further, the refer-

ence stability with temperature is improved over older

types of regulators. 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

150

µF 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 coeffi-

cient. The 150

µF 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 22

µF tantalum or 150µF aluminum

covers all cases of bypassing the adjustment terminal.

Without bypassing the adjustment terminal, smaller ca-

pacitors 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

ADJUSTMENT

µF10µF Tantalum, 50µF Aluminum

None

µF22µF Tantalum, 150µF Aluminum

µF

–

THERMAL

LIMIT

VADJ

VOUT

1083/4/5 ADJ BD

VIN

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