3

LT1123

TEMPERATURE (°C)

0

100

200

300

400

25

50

75

100

LT1123 G01

125

Feedback Pin Bias Current vs

Temperature

FEEDBACK PIN VOLTAGE (V)

0

300

400

500

4

LT1123 G04

200

100

0

1

2

3

5

TEMPERATURE (°C)

–50

5.01

5.02

5.03

25

75

LT1123 G06

5.00

4.99

–25

0

50

100

125

4.98

4.97

Output Voltage vs Temperature

TEMPERATURE (°C)

0

0

200

400

600

25

50

75

100

LT1123 G02

125

100

300

500

Minimum Drive Pin Current vs

Temperature

DRIVE CURRENT (mA)

0

0

1.0

2.5

40

80

100

LT1123 G05

0.5

2.0

1.5

20

60

120

140

Drive Pin Saturation Voltage vs

Drive Current

CC

HARA TERISTICS

A

TYPICALPERFOR

CE

The LT1123 is a three pin device designed to be used in

conjunction with a discrete PNP transistor to form an

inexpensive ultra-low dropout regulator. The device incor-

porates a trimmed 5V bandgap reference, error amplifier,

a current-limited Darlington driver, and an internal ther-

mal limit circuit. The internal circuitry connected to the

drive pin is designed to function at the saturation voltage

of the Darlington driver. This allows a resistor to be

inserted in series with the drive pin. This resistor is used

to limit the base drive to the PNP and also to limit the power

dissipation in the LT1123. The value of this resistor will be

defined by the operating requirements of the regulator

circuit. The LT1123 is designed to sink a minimum of

125mA of base current. This is sufficient base drive to

form a regulator circuit which can supply output currents

up to 4A at a dropout voltage of less than 0.75V.

FU CTIO AL DESCRIPTIO

FEEDBACK PIN VOLTAGE (V)

0

0

50

100

150

12

3

4

LT1123 G03

56

200

Drive Current vs Feedback Pin

Voltage

Feedback Pin Bias Current vs

Feedback Pin Voltage