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LT1528

3A Low Dropout Regulator for Microprocessor Applications

Linear Technology 

LT1528

3A Low Dropout Regulator

for Microprocessor Applications

FEATURES

n Dropout Voltage: 0.6V at IOUT = 3A

n Fast Transient Response

n Output Current: 3A

n Quiescent Current: 400μA

n No Protection Diodes Needed

n Fixed Output Voltage: 3.3V

n Controlled Quiescent Current in Dropout

n Shutdown IQ = 125μA

n Stable with 3.3μF Output Capacitor

n Reverse Battery Protection

n No Reverse Output Current

n Thermal Limiting

APPLICATIONS

n Microprocessor Applications

n Post Regulator for Switching Supplies

n 5V to 3.3V Logic Regulator

DESCRIPTION

The LT ®1528 is a 3A low dropout regulator optimized to

handle the large load current transients associated with

the current generation of microprocessors. This device has

the fastest transient response of currently available PNP

regulators and is very tolerant of variations in capacitor

ESR. Dropout voltage is 75mV at 10mA, rising to 300mV

at 1A and 600mV at 3A. The device has a quiescent cur-

rent of 400μA. Quiescent current is well controlled; it does

not increase significantly as the device enters dropout.

The regulator can operate with output capacitors as small

as 3.3μF, although larger capacitors will be needed to

achieve the performance required in most microprocessor

applications. The LT1528 is available with a fixed output

voltage of 3.3V. An external SENSE pin allows adjustment

to output voltages greater than 3.3V, using a simple resis-

tive divider. This allows the device to be adjusted over a

wide range of output voltages, including the 3.3V to 4.2V

range required by a variety of processors from Intel, IBM,

AMD, and Cyrix.

The LT1528 has both reverse input and reverse output

protection and includes a shutdown feature. Quiescent

current drops to 125μA in shutdown. The LT1528 is avail-

able in 5-lead TO-220 and 5-lead DD-PAK packages.

L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other

trademarks are the property of their respective owners.

TYPICAL APPLICATION

Microprocessor Supply with Shutdown

5 IN

OUT 1

VIN =5V

LT1528

4 SHDN

SENSE 2

GND

3

VOUT

15Ω 68Ω + 4 × 47μF*

SOLID TANTALUM

J1 J2

J3

330Ω

VSHDN (PIN 4)

<0.25

>2.80

NC

OUTPUT

OFF

ON

ON

SHORTING

J1

J2

J3

VOUT

3.30

3.45

4.00

*CHOOSE CAPACITORS

TO MEET PROCESSOR

REQUIREMENTS

1528 TA01

Dropout Voltage

0.6

0.5

0.4

0.3

0.2

0.1

0

0 0.5 1.0 1.5 2.0 2.5 3.0

OUTPUT CURRENT (mA)

1528 TA02

1528fb

1

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