The ADM1275 is a hot-swap controller that allows a circuit board to be removed from or inserted into a live backplane. It also features current and voltage readback via an integrated 12-bit analog-todigital converter （ADC）， accessed using a PMBus? interface. The load current is measured using an internal current sense amplifier that measures the voltage across a sense resistor in the power path via the SENSE+ and SENSE? pins. A default limit of 20 mV is set， but this limit can be adjusted， if required， using a resistor divider network from the internal reference voltage to the ISET pin. The ADM1275 limits the current through the sense resistor by controlling the gate voltage of an external N-channel FET in the power path， via the GATE pin. The sense voltage—and， therefore， the load current—is maintained below the preset maximum. The ADM1275 protects the external FET by limiting the time that the FET remains on while the current is at its maximum value. This current limit time is set by the choice of capacitor connected to the TIMER pin. In addition， a foldback resistor network can be used to actively lower the current limit as the voltage across the FET is increased. This helps to maintain constant power in the FET and allows the safe operating area （SOA） to be adhered to in an effective manner.