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THERMAL

LIMIT

GND

VOUT

LT1083/4/5 BD

VIN

–

block DiagraM

applicaTions inForMaTion

The LT1083 family of three-terminal regulators are easy

to use and have all the protection features that are ex-

pected in high performance voltage regulators. They are

short circuit protected, have safe area protection as well

as thermal shutdown to turn off the regulator should the

temperature exceed about 165°C.

These regulators offer lower dropout voltage and more

precisereferencetolerance.Further,thereferencestability

with temperature is improved over older types of regula-

tors. The only circuit difference between using the LT1083

family and older regulators is that they require 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 150µF aluminum 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

characteristics 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.

Normally, capacitor values on the order of 100µF are used

in the output of many regulators to ensure good transient

response with heavy load current changes. Output capaci-

tance can be increased without limit and larger values of

output capacitance further improve stability and transient

response of the LT1083 regulators.

Anotherpossiblestabilityproblemthatcanoccurinmono-

lithic IC regulators is current limit oscillations. These can

occur because in current limit the safe area protection

exhibits a negative impedance. The safe area protection

decreases the current limit as the input-to-output volt-

age increases.That is the equivalent of having a negative

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