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Power Over Ethernet Interoperability Guide by Sanjaya Maniktala

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Brief Overview of Overloads and Shorts as Per AF Standard
In Fig. 6.1 we show what happens as per the AF standard, when the port current IPORT, ratchets upward. ICONT is the maximum continuous current rating and equals 15.4 W/VPORT (default Class 0/3 assumed). In the figure we also see ICUT, the overload current, and TCUT, the overload timer (which later became TOVLD in the AT standard). In addition, the AF standard has a TLIM timer of 50 to 75 ms too, which starts when the current limit is encountered. As indicated, in the figure, we have sketched the actual ICUT and ILIM of a given chip, as well as its actual TCUT. As the port encounters these levels, timers are actuated. If for example, the overload persists long enough that TCUT timer times ...

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