LT1521/LT1521-3

LT1521-3.3/LT1521-5

1

Rev. C

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TYPICAL APPLICATION

FEATURES

DESCRIPTION

300mA Low Dropout

Regulators with Micropower

Quiescent Current and Shutdown

The LT®1521/LT1521-3/LT1521-3.3/LT1521-5 are low

dropout regulators with micropower quiescent current

and shutdown. These devices are capable of supply-

ing 300mA of output current with a dropout voltage

of 0.5V. Designed for use in battery-powered systems,

the low quiescent current, 12µA operating and 6µA in

shutdown, makes them an ideal choice. The quiescent

current is well controlled; it does not rise in dropout as it

does with many other low dropout PNP regulators.

Other features of the LT1521/LT1521-3/LT1521-3.3/

LT1521-5 include the ability to operate with very small

output capacitors. They are stable with only 1.5µF on the

output while most older devices require between 10µF

and 100µF for stability. Small ceramic capacitors can be

used, enhancing manufacturability. Also, the input may

be connected to voltages lower than the output voltage,

including negative voltages, without reverse current flow

from output to input. This makes the LT1521 series ideal

for backup power situations where the output is held high

and the input is low or reversed. Under these conditions

only 5µA will flow from the output pin to ground.

APPLICATIONS

n

Dropout Voltage: 0.5V

n

Output Current: 300mA

n

Quiescent Current: 12µA

n

No Protection Diodes Needed

n

Adjustable Output from 3.8V to 20V

n

Fixed Output Voltages: 3V, 3.3V, 5V

n

Controlled Quiescent Current in Dropout

n

Shutdown IQ = 6µA

n

Reverse Battery Protection

n

No Reverse Current

n

Thermal Limiting

n

Low Current Regulator

n

Regulator for Battery-Powered Systems

n

Post Regulator for Switching Supplies

5V Battery-Powered Supply with Shutdown

Dropout Voltage

8

5

1

2

3

+

6V

1.5µF

1µF

5V

300mA

VSHDN (PIN 5) OUTPUT

<0.25

OFF

>2.80

ON

NC

ON

LT1521-5

GND

IN

SHDN

OUT

SENSE

LT1521 • TA01

OUTPUT CURRENT (mA)

0

0

0.1

0.2

0.3

0.4

0.6

50

100

150

200

LT1521 • TA02

250

300

0.5

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