1

LT1123

Low Dropout

Regulator Driver

DESCRIPTIO

S

FEATURE

The LT1123 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 700

µA. The

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

s

Extremely Low Dropout

s

Low Cost

s

Fixed 5V Output, Trimmed to

±1%

s

700

µA Quiescent Current

s

3-Pin TO-92 Package

s

1mV Line Regulation

s

5mV Load Regulation

s

Thermal Limit

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4A Output Current Guaranteed

APPLICATI

TYPICAL

5V Low Dropout Regulator

Dropout Voltage

+

620

Ω

10µF*

SEALED

LEAD ACID

5.4 – 7.2V

* REQUIRED IF DEVICE IS

MORE THAN 6" FROM MAIN

FILTER CAPACITOR

OUTPUT = 5V/4A

10µF

†

LT1123 TA01

+

20

Ω

(LARGER VALUES INCREASE

STABILITY)

MOTOROLA

MJE1123

DRIVE

LT1123

GND

FB

OUTPUT CURRENT (A)

0

0.3

0.4

0.5

4

LT1123 TA02

0.2

0.1

0

1

2

3

5