LT1123 Datasheet, PDF (1/12 Pages) Linear Technology – Low Dropout Regulator Driver

FEATURES
s _{Extremely Low Dropout}
s _{Low Cost}
s _{Fixed 5V Output, Trimmed to ±1%}
s _{700µA Quiescent Current}
s _{3-Pin TO-92 Package}
s _{1mV Line Regulation}
s _{5mV Load Regulation}
s _{Thermal Limit}
s _{4A Output Current Guaranteed}
LT1123
Low Dropout
Regulator Driver
DESCRIPTIO
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 700µA. The
device is available in a low cost TO-92 package.
TYPICAL APPLICATI
5V Low Dropout Regulator
SEALED
LEAD ACID
5.4 – 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
Dropout Voltage
0.5
0.4
0.3
0.2
0.1
0
0
1
2
3
4
5
OUTPUT CURRENT (A)
LT1123 TA02
1