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Fabricante

LT1585A

5A Low Dropout Fast Response Positive Regulators Adjustable and Fixed

Linear Technology 

W

W

SI PLIFIED SCHE ATIC

VIN

LT1585A/LT1585A-3.3

THERMAL

LIMIT

ADJ

GND

FOR FIXED VOLTAGE DEVICE

VOUT

LT1585A • BD

APPLICATIONS INFORMATION

General

The LT1585A/LT1585A-3.3 3-terminal regulators are

easy to use and have all the protection features expected

in high performance linear regulators. The devices are

short-circuit protected, safe-area protected and provide

thermal shutdown to turn off the regulators should the

junction temperature exceed about 150°C. The regulators

include an adjustable and a fixed 3.3V version.

These ICs are pin compatible with the LT1083/LT1084/

LT1085 family of linear regulators but offer lower dropout

voltage and faster transient response. The trade-off for this

improved performance is a 7V maximum supply voltage.

Similar to the LT1083/LT1084/LT1085 family, the

LT1585A/LT1585A-3.3 regulators require an output ca-

pacitor for stability. However, the improved frequency

compensation permits the use of capacitors with much

lower ESR while still maintaining stability. This is critical in

addressing the needs of modern, low voltage, high speed

microprocessors.

Current generation microprocessors cycle load current

from almost zero to amps in tens of nanoseconds. Output

voltage tolerances are tighter and include transient re-

sponse as part of the specification. The LT1585A/

LT1585A-3.3 are specifically designed to meet the fast

current load-step requirements of these microprocessors

and save total cost by needing less output capacitance in

order to maintain regulation.

Stability

The circuit design in the LT1585A/LT1585A-3.3 requires

the use of an output capacitor as part of the frequency

compensation. For all operating conditions, the addition

of a 22µF solid tantalum or a 100µF aluminum electrolytic

on the output ensures stability. Normally, the LT1585A/

LT1585A-3.3 can use smaller value capacitors. Many

different types of capacitors are available and have widely

varying characteristics. These capacitors differ in capaci-

5

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