Features

• High Voltage Operation up to 72V
• Synchronizable Operating Frequency and Output Switch Phase for Multiple Controller Systems
• Synchronous Switch Output
• Undervoltage Lockout Protection with 6V Hysteresis for Self-Biased Power
• Fixed Frequency Operation to 350kHz
• Local 1% Voltage Reference
• Input Overvoltage Protection
• Low Start-Up Current
• Programmable Start Inhibit for Power Supply Sequencing and Protection
• Optocoupler Support
• Soft-Start Control

Typical Application

Description

The LT3781 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 LT3781 is ideal for output derived power schemes, through the use of a large undervoltage lockout hysteresis range. The part is also equipped with an 18V V_CC shunt regulator, which prevents exceeding absolute maximum ratings while in trickle start applications.

The LT3781’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 LT3781 is available in a 20-lead SSOP package.