T2P (type 2 PSE) is an active-low multifunction pin that indicates if
[(PSE = Type_2) + (1.5 V < VAPD) + (1.55 V < VPPD< 8.3 V)] × (VCTL < 4 V) × (pd current limit ≠ Inrush).
The term with VCTL prevents an optocoupler connected to the secondary-side from loading VC before the converter is started. The APD and PPD terms allow the PD to operate from an adapter at high-power if a type 2 PSE is not present, assuming the adapter has sufficient capacity. Applications must monitor the state of T2P to detect power source transitions. Transitions could occur when a local power supply is added or dropped or when a PSE is enabled on the far end. The PD may be required to adjust the load appropriately. The usage of T2P is demonstrated in Figure 27.
For a type 2 PD to operate at less than 13 W the first 80 ms after power application, the various delays must be estimated and used by the application controller to meet the requirement. The bootup time of many applications processors may be long enough to eliminate the need to do any timing.