7

LT1584/LT1585/LT1587

General

The LT1584/LT1585/LT1587 family of three-terminal

regulators is easy to use and has all the protection features

expected in high performance linear regulators. The de-

vices 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

LT1584/LT1585/LT1587 family includes adjustable and

fixed voltage versions.

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 LT1584/

LT1585/LT1587 regulators require an output capacitor 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 LT1584/LT1585/

LT1587 family is specifically designed to meet the fast

current load-step requirements of these microprocessors

and saves total cost by needing less output capacitance in

order to maintain regulation.

Stability

The circuit design in the LT1584/LT1585/LT1587 family

requires the use of an output capacitor as part of the

frequency compensation. For all operating conditions, the

addition of a 22

µF solid tantalum or a 100µF aluminum

electrolytic on the output ensures stability. Normally, the

LT1584/LT1585/LT1587 can use smaller value capacitors.

Many different types of capacitors are available and have

widely varying characteristics. These capacitors differ in

capacitor tolerance (sometimes ranging up to

±100%),

equivalent series resistance, equivalent series inductance,

and capacitance temperature coefficient. The LT1584/

LT1585/LT1587 frequency compensation optimizes fre-

quency response with low ESR capacitors. In general, use

capacitors with an ESR of less than 1

Ω.

On the adjustable LT1584/LT1585/LT1587, bypassing the

adjust terminal improves ripple rejection and transient

response. Bypassing the adjust pin increases the required

output capacitor value. The value of 22

µF tantalum or

THERMAL

LIMIT

GND

FOR FIXED VOLTAGE DEVICE

LT1584 • BD

ADJ

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SI PLIFIED SCHE ATIC