Many Power-over-Ethernet (PoE) power sourcing equipment (PSE) single port applications require real-time knowledge of the powered device (PD) current used after startup. The MAX5971A PSE controller with an Integrated MOSFET is capable of delivering up to 40W in to a single port using endpoint or midspan modes. The MAX5971A features current foldback during startup and normal operation, an internal sense resistor for monitoring continuous overcurrent and short-circuit conditions. The MAX5971A powers down the port for continuous overstress. However, no mechanism is available for real-time monitoring and reporting of the actual current sent to the PD during normal operation.
This application note details a method to obtain real-time current monitoring and reporting of the actual current sent to the PD. It uses a MAX4080 high-side, current-sense amplifier, and a current sense resistor on the PSE high-side power path.