LT3681 - 36V, 2A, 2.8MHz Step-Down Switching Regulator with Integrated Power Schottky Diode


  • Wide Input Voltage Range: 3.6V to 34V Operating, 36V Maximum
  • 2A Maximum Output Current
  • Low Ripple Burst Mode Operation
     50µA IQ at 12VIN to 3.3VOUT
     Output Ripple < 15mVP-P
  • Adjustable Switching Frequency: 300kHz to 2.8MHz
  • Low Shutdown Current: IQ < 1µA
  • Integrated Boost Diode
  • Integrated Power Schottky Diode
  • Power Good Flag
  • Saturating Switch Design: 0.18Ω On-Resistance
  • 1.265V Feedback Reference Voltage
  • Output Voltage: 1.265V to 20V
  • Soft-Start Capability
  • Small 14-Pin Thermally Enhanced (4mm x 3mm) DFN Package

Typical Application

LT3681 Typical Application
LT3681 Typical Application


The LT3681 is an adjustable frequency (300kHz to 2.8MHz) monolithic buck switching regulator that accepts input voltages up to 34V (36V maximum). A high efficiency 0.18O switch is included on the die along with a boost Schottky diode and the necessary oscillator, control, and logic circuitry. An undedicated power Schottky diode is integrated into the LT3681 to minimize the solution size. 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. In addition, the LT3681 can further enhance low output current efficiency by drawing bias current from the output when VOUT is above 3V. Shutdown reduces input supply current to less than 1µA while a resistor and capacitor on the RUN/SS pin provide a controlled output voltage ramp (soft-start). A power good flag signals when VOUT reaches 90% of the programmed output voltage. The LT3681 is available in 14-Pin 4mm x 3mm DFN package with exposed pads 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
LT3681EDE#PBF 4x3 DFN-14 DE14MA E 05-08-1731 Yes
LT3681EDE#TRPBF 4x3 DFN-14 DE14MA E 05-08-1731 Yes

LT3681 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
LT3681EDE#PBF 4x3 DFN-14 E $5.21 $3.65 Yes
LT3681EDE#TRPBF 4x3 DFN-14 E $3.71 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
DC1122A LT3681EDE Demo Board | Integrated Boost/Catch Diodes, 4.5V ≤ VIN ≤ 34V, Vout = 3.3V @ 2A $150.00
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Click here to view our complete list of demo boards


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Design Tools


LTspice® software is a powerful, fast and free simulation tool, schematic capture and waveform viewer with enhancements and models for improving the simulation of switching regulators. Click here to download LTspice

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