Datasheet

1
LT1121/LT1121-3.3/LT1121-5
Micropower Low Dropout
Regulators with Shutdown
D
U
ESCRIPTIO
S
F
EA
T
U
RE
■
0.4V Dropout Voltage
■
150mA Output Current
■
30µA Quiescent Current
■
No Protection Diodes Needed
■
Adjustable Output from 3.8V to 20V
■
3.3V and 5V Fixed Output Voltages
■
Controlled Quiescent Current in Dropout
■
Shutdown
■
16µA Quiescent Current in Shutdown
■
Stable with 0.33µF Output Capacitor
■
Reverse Battery Protection
■
No Reverse Current with Input Low
■
Thermal Limiting
The LT1121/LT1121-3.3/LT1121-5 are micropower low
dropout regulators with shutdown. These devices are
capable of supplying 150mA of output current with a
dropout voltage of 0.4V. Designed for use in battery-
powered systems, the low quiescent current, 30µA oper-
ating and 16µA in shutdown, makes them an ideal choice.
The quiescent current is well-controlled; it does not rise in
dropout as it does with many other low dropout PNP
regulators.
Other features of the LT1121/LT1121-3.3/LT1121-5 in-
clude the ability to operate with very small output capaci-
tors. They are stable with only 0.33µF on the output while
most older devices require between 1µF and 100µF for
stability. Small ceramic capacitors can be used, enhanc-
ing manufacturability. Also the input may be connected to
ground or a reverse voltage without reverse current flow
from output to input. This makes the LT1121 series ideal
for backup power situations where the output is held high
and the input is at ground or reversed. Under these
conditions only 16µA will flow from the output pin to
ground.
U
S
A
O
PP
L
IC
AT
I
■
Low Current Regulator
■
Regulator for Battery-Powered Systems
■
Post Regulator for Switching Supplies
U
A
O
PP
L
IC
AT
ITY
P
I
CA
L
5V Battery-Powered Supply with Shutdown
OUTPUT CURRENT (mA)
0
DROPOUT VOLTAGE (V)
0.3
0.4
0.5
60 100 160
0.2
0.1
0
20 40
80
120 140
LT1121 • TA02
Dropout Voltage
IN
OUT
LT1121-3.3
GND
3.3V OUT
150mA
1µF
SOLID TANTALUM
5V
8
+
5
1
3
LT1121 • TA01
V
SHDN
(PIN 5)
< 0.25
> 2.8
 NC
OUTPUT
OFF
ON
ON
SHDN