The waveforms of Figure 22 demonstrate detection, classification, and start-up from a PSE with type 2 hardware classification. The key waveforms shown are VVDD-VVSS, VRTN-VVSS, and IPI. IEEE 802.3at requires a minimum of two detection levels, two class and mark cycles, and start-up from the second mark event. VRTN to VSS falls as the TPS23754 charges CIN following application of full voltage. Subsequently, the converter starts up, drawing current as seen in the IPI waveform.