The ADM1075 is a full feature， negative voltage， hot swap control-ler with constant power foldback and high accuracy digital current and voltage measurement that allows boards to be safely inserted and removed from a live ?48 V backplane. The part provides precise and robust current limiting and protection against both transient and nontransient short circuits and overvoltage and undervoltage conditions. The ADM1075 typically operates from a negative voltage of ?35 V to ?80 V and， due to shunt regulation， has excellent voltage transient immunity. The operating range of the part is flexible due to the shunt regulator， and the part can be powered directly by a 10 V rail to save shunt power dissipation （see the Powering the ADM1075 section for more details）。

　　A full-scale current limit of 25 mV or 50 mV can be selected by choosing the appropriate model. The maximum current limit is set by the combination of the sense resistor， RSENSE， and the input voltage on the ISET pin， using external resistors. This allows fine tuning of the trip voltage so that standard sense resistors can be used. Inrush current is limited to this programmable value by controlling the gate drive of an external N-channel FET. A built-in soft start function allows control of the inrush current profile by an external capacitor on the soft start （SS） pin.

　　An external capacitor on the TIMER pin determines the maxi-mum allowed on-time for when the system is in current limit. This is based on the safe operating area （SOA） limits of the MOSFET. A constant power foldback scheme is used to control the power dissipation in the MOSFET during power-up and fault conditions. The ADM1075 regulates the current dynami-cally to ensure that the power in the MOSFET is within SOA limits as VDS changes. After the timer has expired， the device shuts down the MOSFET. The level of this power， along with the TIMER regulation time， can be set to ensure that the MOSFET remains within the SOA limits.