1. Products
  2. Power Management
  3. Switching Regulators
  4. Flyback, Forward, and Isolated Controller
  5. LT1681


Features and Benefits

  • High Voltage: Operation Up to 72V
  • Synchronizable Operating Frequency and Output Switch Phase for Multiple Controller Systems
  • Fixed Frequency Operation to 350kHz
  • Adaptive and Adjustable Blanking
  • Synchronous Rectifier Driver
  • Local 1% Voltage Reference
  • Undervoltage Lockout Protection with Hysteresis
  • Input Overvoltage Protection
  • Programmable Start Inhibit
  • Transformer Primary Saturation Protection
  • Optocoupler Feedback Support
  • Soft-Start Control

Product Details

The LT1681 controller simplifies the design of high power synchronous dual transistor forward DC/DC converters. The part employs fixed frequency current mode control and supports both isolated and nonisolated topologies. The IC drives external N-channel power MOSFETs and operates with input voltages up to 72V.

The LT1681’s operating frequency is programmable and can be synchronized up to 350kHz. Switch phase is also controlled during synchronized operation to accommodate multiple converter systems. Internal logic guarantees 50% maximum duty cycle operation to prevent transformer saturation.

The LT1681 incorporates a soft-start feature that provides a controlled increase in supplied current during start-up and after an undervoltage lockout or overvoltage/overcurrent event.

The part is available in a 20-lead wide SO package to support high voltage pin-to-pin clearance.


  • Isolated Telecommunication Systems
  • Personal Computers and Peripherals
  • Lead Acid Battery Backup Systems
  • Automotive and Heavy Equipment

Product Lifecycle icon-recommended Production

At least one model within this product family is in production and available for purchase. The product is appropriate for new designs but newer alternatives may exist.

Tools & Simulations


LTspice® is a powerful, fast and free simulation software, schematic capture and waveform viewer with enhancements and models for improving the simulation of analog circuits.


Models for the following parts are available in LTspice:


Design Resources

ADI has always placed the highest emphasis on delivering products that meet the maximum levels of quality and reliability. We achieve this by incorporating quality and reliability checks in every scope of product and process design, and in the manufacturing process as well.  "Zero defects" for shipped products is always our goal.View our quality and reliability program and certifications for more information.

Part Number Material Declaration Reliability Data Pin/Package Drawing CAD Symbols, Footprints & 3D Models
LT1681ESW#PBF Material Declaration Reliability Data 20-Lead SOIC (Wide 0.3 Inch)
LT1681ESW#TRPBF Material Declaration Reliability Data 20-Lead SOIC (Wide 0.3 Inch)
LT1681ISW#PBF Material Declaration Reliability Data 20-Lead SOIC (Wide 0.3 Inch)
LT1681ISW#TRPBF Material Declaration Reliability Data 20-Lead SOIC (Wide 0.3 Inch)
Wafer Fabrication Data R352 Reliability Data

PCN-PDN Information

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Sample & Buy

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Buy Now Pricing

(**) Displayed Buy Now Price and Price Range is based on small quantity orders.


List Pricing

(*)The 1Ku 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 Analog Devices, Inc. authorized distributor. Pricing displayed for Evaluation Boards and Kits is based on 1-piece pricing.


Lead Times

Please see the latest communication from our CCO regarding lead times.



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