1

LT1121/LT1121-3.3/LT1121-5

Micropower Low Dropout

Regulators with Shutdown

DESCRIPTIO

S

FEATURE

s

0.4V Dropout Voltage

s

150mA Output Current

s

30

µA Quiescent Current

s

No Protection Diodes Needed

s

Adjustable Output from 3.8V to 20V

s

3.3V and 5V Fixed Output Voltages

s

Controlled Quiescent Current in Dropout

s

Shutdown

s

16

µA Quiescent Current in Shutdown

s

Stable with 0.33

µF Output Capacitor

s

Reverse Battery Protection

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No Reverse Current with Input Low

s

Thermal Limiting

The LT1121/LT1121-3.3/LT1121-5 are micropower low

dropout regulators with shutdown. These devices are

capable of supplying 150mA of output current with a

dropout voltage of 0.4V. Designed for use in battery-

powered systems, the low quiescent current, 30

µA oper-

ating and 16

µA 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 LT1121/LT1121-3.3/LT1121-5 in-

clude the ability to operate with very small output capaci-

tors. They are stable with only 0.33

µF on the output while

most older devices require between 1

µF and 100µF for

stability. Small ceramic capacitors can be used, enhanc-

ing manufacturability. Also the input may be connected to

ground or a reverse voltage without reverse current flow

from output to input. This makes the LT1121 series ideal

for backup power situations where the output is held high

and the input is at ground or reversed. Under these

conditions only 16

µA will flow from the output pin to

ground.

S

APPLICATI

s

Low Current Regulator

s

Regulator for Battery-Powered Systems

s

Post Regulator for Switching Supplies

APPLICATI

TYPICAL

5V Battery-Powered Supply with Shutdown

OUTPUT CURRENT (mA)

0

0.3

0.4

0.5

60

100

160

0.2

0.1

0

20

40

80

120 140

LT1121 • TA02

Dropout Voltage

IN

OUT

LT1121-3.3

GND

3.3V OUT

150mA

1

µF

SOLID TANTALUM

5V

8

+

5

1

3

LT1121 • TA01

< 0.25

> 2.8

NC

OUTPUT

OFF

ON

ON

SHDN