LT1587-1.5 Просмотр технического описания (PDF) - Linear Technology

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LT1587-1.5

Fixed 1.5V, 3A Low Dropout Fast Response GTL+ Regulator

Linear Technology 

LT1587-1.5

W

W

SI PLIFIED SCHE ATIC

VIN

THERMAL

LIMIT

GND

VOUT

LT1587 • BD

APPLICATIONS INFORMATION

General

The LT1587-1.5 3-terminal regulator is easy to use and

has all the protection features expected in a high perfor-

mance linear regulator. The device is short-circuit pro-

tected, safe-area protected and provides thermal shut-

down to turn off the regulator if the junction temperature

exceeds about 150°C.

The IC is pin compatible with the LT1083/LT1084/LT1085

family of linear regulators but offers lower dropout voltage

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

proved performance is a 7V maximum supply voltage.

Similar to the LT1083/LT1084/LT1085 family, the LT1587-

1.5 regulator requires 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 and their associated

circuitry cycle load current from almost zero to several

amps in tens of nanoseconds. Output voltage tolerances

are tighter and include transient response as part of the

specification. The LT1587-1.5 is specifically designed to

meet the fast current load step requirements of these

applications and saves total cost by needing less output

capacitance in order to maintain regulation.

Stability

The circuit design in the LT1587-1.5 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 LT1587-1.5 can use smaller

value capacitors. Many different types of capacitors are

available and have widely varying characteristics. These

capacitors differ in capacitor tolerance (sometimes rang-

ing up to ±100%), equivalent series resistance, equivalent

series inductance and capacitance temperature coefficient.

The LT1587-1.5 frequency compensation optimizes fre-

quency response with low ESR capacitors. In general, use

capacitors with an ESR of less than 1Ω.

Normally, capacitor values on the order of several hundred

microfarads are used on the output of the regulators to

ensure good transient response with heavy load current

changes. Output capacitance can increase without limit

and larger values of output capacitance further improve the

stability and transient response of the LT1587-1.5.

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