Abstract: A power budget monitoring circuit in a multi-port PSE includes a differential amplifier and a transistor for setting a reference voltage across a first resistor to establish a reference current, multiple current mirror output devices each associated with a power port of the PSE, a second resistor and a comparator. Each current mirror output device provides an output current indicative of the power demanded by the associated power port where the output currents are summed at a second node into a monitor current. The second resistor has a resistance value proportional to a maximum power budget of the PSE and receives the monitor current. A monitor voltage develops across the second resistor indicative of the total power demanded by the power ports. The comparator compares the monitor voltage to the reference voltage and provides a comparator output signal indicating whether the maximum power budget of the PSE has been exceeded.

Abstract: An AC maintain power signature detection circuit in a power sourcing equipment (PSE) for a Power over Ethernet system injects an AC test signal onto a power port of the PSE. The AC test signal is driven onto a first power terminal of the power port through a sense resistor. The voltages across the sense resistor are measured and scaled by first and second resistor dividers having different resistor ratios. The voltage and the scaled voltage at the first power terminal side of the sense resistor have a peak voltage being proportional to the load impedance of the load coupled to the power port. The comparator compares the scaled voltages measured across the sense resistor and generates the output signal indicative of the load impedance at the power port.

Abstract: An AC maintain power signature detection circuit in a power sourcing equipment (PSE) for a Power over Ethernet system injects an AC test signal onto a power port of the PSE. The AC test signal is driven onto a first power terminal of the power port through a sense resistor. The voltages across the sense resistor are measured and scaled by first and second resistor dividers having different resistor ratios. The voltage and the scaled voltage at the first power terminal side of the sense resistor have a peak voltage being proportional to the load impedance of the load coupled to the power port. The comparator compares the scaled voltages measured across the sense resistor and generates the output signal indicative of the load impedance at the power port.

Abstract: A power budget monitoring circuit in a multi-port PSE includes a differential amplifier and a transistor for setting a reference voltage across a first resistor to establish a reference current, multiple current mirror output devices each associated with a power port of the PSE, a second resistor and a comparator. Each current mirror output device provides an output current indicative of the power demanded by the associated power port where the output currents are summed at a second node into a monitor current. The second resistor has a resistance value proportional to a maximum power budget of the PSE and receives the monitor current. A monitor voltage develops across the second resistor indicative of the total power demanded by the power ports. The comparator compares the monitor voltage to the reference voltage and provides a comparator output signal indicating whether the maximum power budget of the PSE has been exceeded.