The TPS23753A is in detection mode whenever V_VDD-VSS is below the lower classification threshold. When the input voltage rises above V_{CL_ON}, the DEN pin goes to an open-drain condition to conserve power. While in detection, RTN is high impedance, almost all the internal circuits are disabled, and the DEN pin is pulled to V_SS. An R_DEN of 24.9 kΩ (1%), presents the correct signature. It may be a small, low-power resistor because it only sees a stress of about 5 mW. A valid PD detection signature is an incremental resistance between 23.75 kΩ and 26.25 kΩ at the PI.

The detection resistance seen by the PSE at the PI is the result of the input bridge resistance in series with the parallel combination of R_DEN and the TPS23753A bias loading. The incremental resistance of the input diode bridge may be hundreds of ohms at the very low currents drawn when 2.7 V is applied to the PI. The input bridge resistance is partially cancelled by the effective resistance of the TPS23753A during detection.