LT1121/LT1121-3.3/LT1121-5
Micropower Low Dropout
Regulators with Shutdown
FEATURES
DESCRIPTION
0.4V Dropout Voltage
n 150mA Output Current
n 30µA Quiescent Current
n No Protection Diodes Needed
n Adjustable Output from 3.75V to 30V
n 3.3V and 5V Fixed Output Voltages
n Controlled Quiescent Current in Dropout
n Shutdown
n 16µA Quiescent Current in Shutdown
n Stable with 0.33µF Output Capacitor
n Reverse Battery Protection
n No Reverse Current with Input Low
n Thermal Limiting
n Available in the 8-Lead SO, 8-Lead PDIP, 3-Lead
SOT-23 and 3-Lead TO-92 Packages
The LT®1121/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 operating 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.
n
APPLICATIONS
Low Current Regulator
Regulator for Battery-Powered Systems
n Post Regulator for Switching Supplies
n
n
Other features of the LT1121/LT1121-3.3/LT1121-5 include
the ability to operate with very small output capacitors.
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, enhancing 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.
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. All other trademarks are the property of their respective owners.
TYPICAL APPLICATION
5V Battery-Powered Supply with Shutdown
Dropout Voltage
0.5
IN
OUT
1
LT1121-3.3
5V
5
+
SHDN
GND
3
VSHDN (PIN 5) OUTPUT
<0.25
OFF
>2.8
ON
NC
ON
3.3VOUT
150mA
1μF
SOLID TANTALUM
0.4
DROPOUT VOLTAGE (V)
8
0.3
0.2
0.1
LT1121 • TA01
0
0
20
40 60 80 100 120 140 160
OUTPUT CURRENT (mA)
LT1121 • TA02
1121fg
1
