The LTC4240 is a Hot SwapTM controller that allows a board to be safely inserted and removed from a live CompactPCI bus slot. The LTC4240 has a built-in 2-wire I2C compatible interface to allow software control and monitoring of device function and power supply status. Two external N-channel transistors control the 3.3V and 5V supplies, while two internal switches control the 12V and 12V supplies. Electronic circuit breakers protect all four supplies against overcurrent faults. The PWRGD output indicates when all of the supply voltages are within tolerance. The OFF/ON pin is used to cycle the board power or reset the circuit breaker. The I2C interface allows the user to turn the device off or on, set RESETOUT, turn on the status LED driver and ignore 12V, 12V faults. It also allows the user to read the status of the FAULT, RESETIN, RESETOUT, PWRGD, PRSNT1# and PRSNT2# pins. Under a fault condition, the I2C interface can also be used to determine which of the four supplies generated the fault. The LTC4240 is available in a 28-pin narrow SSOP package.