The LTC4253/LTC4253A negative voltage Hot Swap™controllers allow 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 LTC4253/LTC4253A latch off after a circuit fault.Adjustable undervoltage and overvoltage detectors disconnect the load whenever the input supply exceeds the desired operating range. The LTC4253/LTC4253A’s supply input is shunt-regulated, allowing safe operation with very high supply voltages. A multifunction timer delays initial startup 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 soft-start 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 LTC4253A features tight ±1% undervoltage/ overvoltage threshold accuracy. The LTC4253/LTC4253A are available in a 16-pin SSOP.NotesLTC4253LTC4253ARecommendLTC4253Bfor new designsLTC4253A-ADJRecommendLTC4253Bfor new designsLTC4253BApplications-48V Distributed Power SystemsNegative Power Supply ControlCentral Office SwitchingHigh Availability ServersDisk Arrays