Power over data lines system with accurate and simplified cable resistance sensing

摘要

In a PoDL system, where DC power and differential data are supplied over the same conductors between a PSE and a PD, a low-power test is first performed to determine the conductor resistance. The PSE and PD are connected to the conductors via DC-coupling inductors that block the data signals. Such inductors have a DC resistance (DCR). To avoid the DCR of the PD inductors being included in the resistance test of the conductors and to avoid the requirement of additional pins for kelvin sensing, the PD includes a MOSFET switch connected across the conductors on the line-side of the PD inductors. The PSE applies a current pulse of a known value to one of the conductors while the MOSFET switch is temporarily closed. The PSE measures the resulting voltage across the wires and uses Ohm's law to more accurately calculate the resistance of the conductors.