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LTC4253B - –48V Hot Swap Controller with Sequencer

The LTC®4253B negative voltage Hot Swap™ controller allows a board to be safely inserted and removed from a live backplane. Output current is controlled by three stages of current-limiting: a timed circuit breaker, active current limiting and a fast feedforward path that limits peak current under worst-case catastrophic fault conditions. The LTC4253B latches off after a circuit fault.

Adjustable undervoltage and overvoltage detectors disconnect the load whenever the input supply exceeds the desired operating range. The LTC4253B’s supply input is shunt-regulated, allowing safe operation with very high supply voltages. A multifunction timer delays initial start-up and controls the circuit breaker’s response time. The circuit breaker’s response time can be accelerated by sensing excessive MOSFET drain voltage, keeping the MOSFET within its safe operating area (SOA). An adjustable softstart circuit controls MOSFET inrush current at start-up.

Three power good outputs are sequenced by an adjustable timer and two ENABLE inputs to enable external power modules at start-up or disable them if the circuit breaker trips. The LTC4253B improves the ruggedness of the LTC4253 shunt regulator.

Features Allows Safe Board Insertion and Removal from a Live –48V Backplane Floating Topology Permits Very High Voltage Operation Adjustable Analog Current Limit with Breaker Timer Ideal for Two Battery Feeds Fast Response Time Limits Peak Fault Current Three Sequenced Power Good Outputs Improved Ruggedness Shunt Regulator Adjustable Soft-Start Current Limit Adjustable Timer with Drain Voltage Accelerated Response Latchoff After Fault Available in a 16-Pin SSOP Package Typical Application

Applications –48V Distributed Power Systems Negative Power Supply Control Central Office Switching High Availability Servers Disk Arrays Packaging

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