Power Over Ethernet Interoperability Guide

Device Dependency in the AF Standard

Consider the fact that in the AF standard, as per Table 33-5, page 42, I_CUT is expressed as a range extending from P_CLASS/V_PORT to 0.4 A. But, looking carefully also at Figure 33C.6, page 97 of the AF standard, we realize that what is really being implied by stating it in this manner is that the systems/IC designer needs to target a nominal value for I_CUT centered somewhere roughly in the middle of this range (say 375 mA), and also ensure that the min and max values of this parameter I_CUT are always within the prescribed limits—P_CLASS/V_PORT to 0.4 A, all tolerances, drifts, and so on considered. The understanding is that whenever the actual set threshold of a given PSE device is exceeded, its internal comparator ...