LT1123 - Low Dropout Regulator Driver


  • Extremely Low Dropout
  • Low Cost
  • Fixed 5V Output, Trimmed to ±1%
  • 700µA Quiescent Current
  • 3-Pin TO-92 Package
  • 1mV Line Regulation
  • 5mV Load Regulation
  • Thermal Limit
  • 4A Output Current Guaranteed

Typical Application

LT1123 Typical Application
LT1123 Typical Application


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.


CAD Symbols and Footprints: The downloadable Zip file below contains the schematic symbol and PCB footprints.

For complete and up to date package information and drawings, please refer to our packaging page

Part Number Package Code Temp Package
LT1123CST#PBF SOT-223 ST C 05-08-1630 Yes
LT1123CST#TRPBF SOT-223 ST C 05-08-1630 Yes
LT1123CZ#PBF TO-92 Z C 05-08-1410 Yes
LT1123CZ#TRPBF TO-92 Z C 05-08-1410 Yes

LT1123 Package Drawing
LT1123 Package Drawing

Order Info

  • Part numbers ending in PBF are lead free. Solder plated terminal finish (SnPb) versions are non-standard and special terms and conditions and pricing applies if available. Please contact LTC marketing for information.
  • Part numbers containing TR or TRM are shipped in tape and reel or 500 unit mini tape and reel, respectively
  • Please refer to our general ordering information or the product datasheet for more details

Package Variations and Pricing

Part Number Package Temp Price
LT1123CST#PBF SOT-223 C $2.08 $1.65 Yes
LT1123CST#TRPBF SOT-223 C $1.71 Yes
LT1123CZ#PBF TO-92 C $1.58 $1.25 Yes
LT1123CZ#TRPBF TO-92 C $1.31 Yes
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* The USA list pricing shown is for BUDGETARY USE ONLY, shown in United States dollars (FOB USA per unit for the stated volume), and is subject to change. International prices may differ due to local duties, taxes, fees and exchange rates. For volume-specific price or delivery quotes, please contact your local Linear Technology sales office or authorized distributor.

Demo Boards

Linear Technology offers many demo boards free of charge to qualified customers. Contact your local sales office or distributor to inquire about a demo board. Certain demo boards are also available for sale via credit card on this website. Demo boards are for evaluation purposes only. It remains the customer’s responsibility to verify proper and reliable operation in the actual end application.

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Design Tools

Linear Technology provides a variety of custom design simulation tools and device models to allow even novice designers to quickly and easily evaluate circuits using high performance switching regulators, amplifiers, data converters, filters and more. Please visit our Design Tools page to view and download:

  • LTspice - A powerful SPICE simulator, schematic capture and waveform viewer with enhancements and models for easing the simulation of switching regulators
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