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Power Over Ethernet Interoperability Guide by Sanjaya Maniktala

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Undervoltage Lockout Thresholds
The standard also creates undervoltage lockout (UVLO) thresholds when it states that the PD power supply must turn ON by the time the port voltage reaches VON = 42 V. And when the port voltage falls, the PD power supply must turn OFF before the port voltage falls to VOFF = 30 V. Later, the standard makes it even more brief (and rather succinctly confusing), by requiring that the PD turn ON at a port voltage less than VON and turn OFF at a port voltage greater than VOFF. Question is what part of the PD? Neither is it clarified whether the output of the DC-DC converter is expected to be up (and stable) by that rising port voltage level. It seems questionable if these levels have anything to do with the PD power ...

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