ADM1177

The ADM1177 is an integrated hot swap controller that offers digital current and voltage monitoring via an on-chip, 12-bit analog-to-digital converter (ADC), communicated through an I²C interface.An internal current sense amplifier senses voltage across the sense resistor in the power path via the VCC pin and the SENSE pin.

The ADM1177 limits the current through this resistor by control-ling the gate voltage of an external N-channel FET in the power path, via the GATE pin. The sense voltage (and, therefore, the inrush current) is kept below a preset maximum.

The ADM1177 protects the external FET by limiting the time that it spends with maximum current running through it. This current limit period is set by the choice of capacitor attached to the TIMER pin. Additionally, the device provides protection from overcurrent events that may occur once the hot swap event is complete. In the case of a short-circuit event, the current in the sense resistor exceeds an overcurrent trip threshold, and the FET is switched off immediately by pulling down the GATE pin.

A soft start (SS) pin is also included. ADM1177 gives the user control over the reference on the current sense amplifier. An internal current source charges a capacitor on this pin at startup, allowing the user to set the profile of the initial current ramp. A voltage can also be driven on this pin to alter the reference.

A 12-bit ADC can measure the current seen in the sense resistor, as well as the supply voltage on the VCC pin. An industry-standard I²C interface allows a controller to read current and voltage data from the ADC. Measurements can be initiated by an I²C command. Alternatively, the ADC can run continuously, and the user can read the latest conversion data whenever ADM1177 is required. Up to four unique I²C addresses can be created, depending on the way the ADR pin is connected. The ADM1177 is packaged in a 10-lead MSOP.