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LTC1698 - Isolated Secondary Synchronous Rectifier Controller

The LTC1698 is a precision secondary-side forward converter controller that synchronously drives external N-channel MOSFETs. It is designed for use with the LT3781 primary-side synchronous forward converter controller to create a completely isolated power supply. The LT3781 synchronizes the LTC1698 through a small pulse transformer and the LTC1698 drives a feedback optocoupler to close the feedback loop. Output accuracy of ±0.8% and high efficiency over a wide range of load currents are obtained.

The LTC1698 provides accurate secondary-side current limit using an external current sense resistor. The input voltage at the MARGIN pin provides ±5% output voltage adjustment. A power good flag and overvoltage input are provided to ensure proper power supply conditions. An auxiliary 3.3V logic supply is included that supplies up to 10mA of output current.

Features High Efficiency Over Wide Load Current Range ±0.8% Output Voltage Accuracy Dual N-Channel MOSFET Synchronous Drivers Pulse Transformer Synchronization Optocoupler Feedback Driver Programmable Current Limit Protection ±5% Margin Output Voltage Adjustment Adjustable Overvoltage Fault Protection Power Good Flag Auxiliary 3.3V Logic Supply Available in 16-Lead SSOP and SO Packages Typical Application

Applications 48V Input Isolated DC/DC Converters Isolated Telecommunication Power Systems Distributed Power Step-Down Converters Industrial Control Systems Automotive and Heavy Equipment Packaging

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