LT3668 - 40V 400mA Step-Down Switching Regulator with Dual Fault Protected Tracking LDOs


  • Dual Low Dropout Linear Tracking Regulators
    200mA Outputs with Programmable Current Limits
    1.6V to 45V Input Range
    Fault Protected to ±45V
  • Triple Output Supply from a Single Input Requires Only One Inductor
  • IQ = 50μA at 12VIN to 6V and 5V with No Load
  • Buck Regulator:
    Low Ripple (<15mVP-P) Burst Mode Operation®
    400mA Output with Internal Power Switch
    4.3V to 40V Input Operation Range (60V Max)
  • Adjustable 250kHz to 2.2MHz Switching Frequency
  • Power Good Indicator
  • Available in a Thermally-Enhanced 16-Lead MSOP Package

Typical Application

LT3668 Typical Application
LT3668 Typical Application


The LT®3668 is a monolithic triple power supply composed of a 400mA buck switching regulator and two 200mA low dropout linear tracking regulators (LDOs).This provides a complete and robust power solution for applications that require the power supply of a sensor to tightly track the power supply of a measurement ASIC.

Each tracking LDO supplies 200mA of output current with a typical dropout voltage of 340mV, and each LDO has an accurate resistor programmable current limit.

Internal protection circuitry includes reverse-battery protection, current limiting, thermal limiting and reverse current protection.

The buck regulator includes a high efficiency switch, a boost diode, and the necessary oscillator, control and logic circuitry. Current mode topology is used for fast transient response and good loop stability. Low ripple Burst Mode operation maintains high efficiency at low output currents while keeping output ripple below 15mV in a typical application.

The LT3668 is available in a thermally-enhanced 16-lead MSOP package with exposed pad for low thermal resistance.


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
LT3668EMSE#PBF MS-16E MSE E 05-08-1667 Yes
LT3668EMSE#TRPBF MS-16E MSE E 05-08-1667 Yes
LT3668HMSE#PBF MS-16E MSE H 05-08-1667 Yes
LT3668HMSE#TRPBF MS-16E MSE H 05-08-1667 Yes
LT3668IMSE#PBF MS-16E MSE I 05-08-1667 Yes
LT3668IMSE#TRPBF MS-16E MSE I 05-08-1667 Yes

LT3668 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
LT3668EMSE#PBF MS-16E E $3.64 $2.55 Yes
LT3668EMSE#TRPBF MS-16E E $2.61 Yes
LT3668HMSE#PBF MS-16E H $4.37 $3.06 Yes
LT3668HMSE#TRPBF MS-16E H $3.12 Yes
LT3668IMSE#PBF MS-16E I $4.02 $2.81 Yes
LT3668IMSE#TRPBF MS-16E I $2.87 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.

Part Number Description Price Documentation
DC2243A LT3668EMSE Demo Board | Buck Plus Dual Post-Regulator LDOs, 7V ≤ VIN ≤ 40V; VOUT1 = 6V @ 0.4A, VOUT2 = 5V @ 0.2A, VOUT3 = 5V @ 0.2A Contact Factory
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Click here to view our complete list of demo boards


  • Fault-Protected Sensor Supply
  • Automotive and Industrial Supplies
  • Power for Portable Instrumentation

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Design Tools


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