LT1123
Low Dropout
Regulator Driver
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FEATURES
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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.
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
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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.
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TYPICAL APPLICATIO
5V Low Dropout Regulator
Dropout Voltage
0.5
+
MOTOROLA
MJE1123
10µF*
20Ω
DRIVE
*REQUIRED IF DEVICE IS
MORE THAN 6" FROM MAIN
FILTER CAPACITOR
†
REQUIRED FOR STABILITY
(LARGER VALUES INCREASE
STABILITY)
OUTPUT = 5V/4A
LT1123 FB
+
GND
10µF†
0.4
DROPOUT VOLTAGE (V)
SEALED
LEAD ACID
5.4 TO 7.2V
620Ω
0.3
0.2
0.1
LT1123 TA01
0
0
1
3
4
2
OUTPUT CURRENT (A)
5
LT1123 TA02
1123fb
1