LINEAR TECHNOLOGY LT1121 LT1121-3.3 LT1121-5 Owner's Manual User Guide
Summary
These micropower low dropout regulators are engineered specifically for robust battery-powered systems requiring minimal energy consumption. Offering fixed 3.3V or 5V outputs and a gentle 150mA current capability, they feature excellent efficiency due to extremely low quiescent currents (down to 16µA in shutdown) and built-in reverse battery protection. The manual provides comprehensive details on electrical characteristics, operating limits across various packages, and specialized application guidance for designers building reliable post-regulators and low-current always-on electronics.
Page 1 Text Content
LT1121/LT1121-3.3/LT1121-5 Micropower Low Dropout Regulators with Shutdown
FEATURES DESCRIPTIO
0.4V Dropout Voltage The LT®1121/LT1121-3.3/LT1121-5 are micropower low 150m A Output Current dropout regulators with shutdown. These devices are 30µA Quiescent Current capable of supplying 150m A of output current with a No Protection Diodes Needed dropout voltage of 0.4V. Designed for use in battery- Adjustable Output from 3.8V to 30V powered systems, the low quiescent current, 30µA oper- 3.3V and 5V Fixed Output Voltages ating and 16µA in shutdown, makes them an ideal choice. Controlled Quiescent Current in Dropout The quiescent current is well-controlled; it does not rise in Shutdown dropout as it does with many other low dropout PNP 16µA Quiescent Current in Shutdown regulators.
Stable with 0.33µF Output Capacitor
Other features of the LT1121/LT1121-3.3/LT1121-5 in-
Reverse Battery Protection
clude the ability to operate with very small output capaci-
No Reverse Current with Input Low
tors. They are stable with only 0.33µF on the output while
Thermal Limiting
most older devices require between 1µF and 100µF for
DR OP OU VO LT AG (V
Available in the 8-Lead SO, 8-Lead PDIP, 3-Lead
stability. Small ceramic capacitors can be used, enhancing
SOT-23 and 3-Lead TO-92 Packages
manufacturability. Also the input may be connected to ground or a reverse voltage without reverse current flow APPLICATIO S from output to input. This makes the LT1121 series ideal for backup power situations where the output is held high
Low Current Regulator and the input is at ground or reversed. Under these Regulator for Battery-Powered Systems conditions only 16µA will flow from the output pin to Post Regulator for Switching Supplies ground.
, LTC and LT are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners.
TYPICAL APPLICATIO 5V Battery-Powered Supply with Shutdown Dropout Voltage
3.3VOUT
IN OUT
5V LT1121-3.3 1µF
SOLID TANTALUM
SHDN GND
VSHDN (PIN 5) OUTPUT
<0.25 OFF >2.8 ON NC ON
LT1121 • TA01
OUTPUT CURRENT (m A)
LT1121 • TA02
1121fc
Page Summary Contents For LINEAR TECHNOLOGY LT1121 LT1121-3.3 LT1121-5 Owner's Manual User Guide
Manual Details
| Brand | Linear |
|---|---|
| Pages | 16 |
| File Size | 161.81 KB |
| Published | June 19, 2026 |
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Frequently Asked Questions
What is the typical power draw and primary current capability?
It can supply 150mA of output current while maintaining a low quiescent current of 30µA.
Does this regulator require standard large capacitors for stability?
No, it is stable even with only 0.33µF on the output capacitor, making small ceramic usage possible.
Is external protection required when using this module?
No external protection diodes are needed for use in battery-powered systems, and it includes reverse battery protection.
What happens if the input voltage is reversed or grounded?
The device can operate with a ground or reversed input voltage without passing current in reverse from output to input.