Features

• 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

Typical Application

Description

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.