LT1123 LINER [Linear Technology], LT1123 Datasheet - Page 3

• Manufacturer Part Number: LT1123
• Description: Low Dropout Regulator Driver
• Manufacturer: LINER [Linear Technology]

FU CTIO AL DESCRIPTIO
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
TYPICAL PERFOR
400
300
200
100
500
400
300
200
100
0
U
Feedback Pin Bias Current vs
Temperature
0
Feedback Pin Bias Current vs
Feedback Pin Voltage
0
V
FB
= 5V
25
1
FEEDBACK PIN VOLTAGE (V)
TEMPERATURE (°C)
U
T
50
J
= 25°C
2
75
T
J
3
= 125°C
100
T
J
W
= 0°C
4
LT1123 G01
LT1123 G04
A
U
125
5
CE
C
600
400
300
200
U
500
100
HARA TERISTICS
1.5
2.5
2.0
1.0
0.5
0
0
0
Drive Pin Saturation Voltage vs
Drive Current
0
Minimum Drive Pin Current vs
Temperature
V
V
DRIVE
FB
20
= 4.5V
25
= 3V
C
40
DRIVE CURRENT (mA)
TEMPERATURE (°C)
T
T
J
J
50
= 25°C
= 0°C
60
T
J
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.
= 125°C
80
75
100
100
120
LT1123 G02
LT1123 G05
125
140
5.03
5.02
4.97
5.01
5.00
4.99
4.98
200
150
100
50
0
–50
Drive Current vs Feedback Pin
Voltage
0
Output Voltage vs Temperature
V
T
DRIVE
J
–25
= 25°C
1
FEEDBACK PIN VOLTAGE (V)
= 3V
0
TEMPERATURE (°C)
2
25
T
J
= –50°C
3
50
T
LT1123
J
4
75
= 125°C
100 125
5
LT1123 G03
LT1123 G06
3
6