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Power Over Ethernet Interoperability Guide by Sanjaya Maniktala

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Setting the Timer for “MPS Valid”
The problem is that a min value is given for TMPS, not a design range. This has caused some confusion, causing some PSE-chip designers and software folks to set the MPS-valid timer at around 40 ms. They make two assumptions when asked: (a) that this is also IEEE-compliant behavior and 60 ms is actually the max if interpreted “correctly,” and (b) by doing so, they end up supporting “green applications,” allowing further reduction in minimum power. However, that is not true. We have to understand that the overriding spirit of the PoE standards is always tilted towards safety. So it would prefer to turn the port OFF rather than keep it alive. Our reasoning has to support this too. So if the PD is designed to ask ...

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