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LT1123CST

Low Dropout Regulator Driver

Linear Technology 

FEATURES

■ Extremely Low Dropout

■ Low Cost

■ Fixed 5V Output, Trimmed to ±1%

■ 700µA Quiescent Current

■ 1mV Line Regulation

■ 5mV Load Regulation

■ Thermal Limit

■ 4A Output Current Guaranteed

■ Available in a 3-Pin TO-92 Package

LT1123

Low Dropout

Regulator Driver

DESCRIPTIO

The LT®1123 is a 3-pin bipolar device designed to be used

in conjunction with a discrete PNP power transistor to

form an inexpensive low dropout regulator. The LT1123

consists of a trimmed bandgap reference, error amplifier,

and a driver circuit capable of sinking up to 125mA from

the base of the external PNP pass transistor. The LT1123

is designed to provide a fixed output voltage of 5V.

The drive pin of the device can pull down to 2V at 125mA

(1.4V at 10mA). This allows a resistor to be used to reduce

the base drive available to the PNP and minimize the

power dissipation in the LT1123. The drive current of the

LT1123 is folded back as the feedback pin approaches

ground to further limit the available drive current under

short-circuit conditions.

Total quiescent current for the LT1123 is only 700µA. The

device is available in a low cost TO-92 package.

, LTC and LT are registered trademarks of Linear Technology Corporation.

All other trademarks are the property of their respective owners.

TYPICAL APPLICATIO

5V Low Dropout Regulator

SEALED

LEAD ACID

5.4 TO 7.2V

+

10µF*

620Ω

20Ω

MOTOROLA

MJE1123

*REQUIRED IF DEVICE IS

MORE THAN 6" FROM MAIN

FILTER CAPACITOR

†REQUIRED FOR STABILITY

(LARGER VALUES INCREASE

STABILITY)

DRIVE

LT1123 FB

GND

OUTPUT = 5V/4A

+

10µF†

LT1123 TA01

0.5

0.4

0.3

0.2

0.1

0

0

Dropout Voltage

1

2

3

4

5

OUTPUT CURRENT (A)

LT1123 TA02

1123fb

1

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