ZHCSA47E July 2012 – January 2018 TPS23751 , TPS23752
PRODUCTION DATA.
The TPS23751 or TPS23752 pulls DEN to VSS whenever V(VDD-VSS) is below the lower classification threshold. When the input voltage rises above VCL-ON, the DEN pin goes to an open-drain condition to conserve power. While in detection, RTN is high impedance, and almost all the internal circuits are disabled. An RDEN of 24.9 kΩ (±1%), presents the correct signature. It may be a small, low-power resistor since it only sees a stress of about 5 mW. A valid PD detection signature is an incremental resistance ( ΔV/ΔI ) 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 RDEN and internal VDD 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 compensated by the TPS23751 or TPS23752 effective resistance during detection.
The type 2 hardware classification protocol of IEEE 802.3at specifies that a type 2 PSE drops its output voltage into the detection range during the classification sequence. The PD is required to have an incorrect detection signature in this condition, which is referred to as a mark event (see Figure 24). After the first mark event, the TPS23751 or TPS23752 presents a signature less than 12 kΩ until it has experienced a V(VDD-VSS) voltage below the mark reset threshold (VMSR). This operation is explained more fully in the Hardware Classification section.