SLVSER6B May 2020 – November 2020 TPS23730
PRODUCTION DATA
The waveforms of Figure 8-7 demonstrate detection, classification, and start-up from a Type 3 or 4 PSE with Class 6 hardware classification. The key waveforms shown are VVDD-VSS, VRTN-VSS, and IPI. IEEE802.3bt and IEEE 802.3at require a minimum of two detection levels; however, four levels are shown in this example. Four levels guard against misdetection of a device when plugged in during the detection sequence.
IEEE 802.3bt also requires a PSE allocating Class 6 level of power to generate four class and mark cycles, and startup from the fourth mark event. As shown below, the required minimum duration of the first class event has been extended for Type 3 and 4 PSEs. VRTN to VSS falls as the TPS23730 charges CBULK following application of full voltage. In Figure 8-9, the converter soft-start is also delayed until the end of inrush period.