ADM1070

The ADM1070 is a negative voltage hot swap controller that allows a board to be safely inserted and removed from a live 48 V backplane. The part achieves this by providing robust current limiting, protection against transient and nontransient short circuits and overvoltage and undervoltage conditions. The ADM1070 typically operates from a negative voltage of up to 80 V and can tolerate transient voltages of up to 200 V.

In-rush current is limited to a programmable value by controlling the gate drive of an external N-channel FET in ADM1070. The current limit can be controlled by the choice of the sense resistor, R_SENSE. Added control of the in-rush current is provided by an on-chip timer that uses pulsewidth modulation to allow the maximum current to flow for only 3% of the time. An autorestart occurs after a current limit timeout. After seven successive autorestarts, the fault will be latched and the part goes into shutdown with the result that the external FET is disabled until the power is reset.

The ADM1070 also features single-pin undervoltage and over-voltage detection. The FET is turned off if a nontransient voltage less than the undervoltage threshold, typically 36 V, or greater than the overvoltage threshold, typically 77 V, is detected on the UV/OV Pin. The operating voltage window of the
ADM1070 is programmable and is determined by the ratio R1/R2. Time filtering on the undervoltage and overvoltage detection and current limiting is programmable via the TIMER Pin. An external capacitor connected between the TIMER Pin and VEE determines the undervoltage/overvoltage time filter and the timeout in current limit. If the pin is tied to VEE, the time filter values and the current limit timeout revert to default figures. The ADM1070 is fabricated using BiCMOS technology for minimal power consumption. The part is available in a small 6-Lead SOT-23 package.