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We have POE 802.3af in our design. We are facing some issues with it as elaborated below.

  1. We have connected an LED load to the connector end with a POE splitter. A splitter is used to convert 48V to 12V. When the board power ON LED glows after a minute, there is some delay found when glowing delay.

  2. What is the ground reference for PoE 48V (VC2+)? Refer to attached image.

enter image description here

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  • \$\begingroup\$ There is no gnd as such for an endpoint as there is a bridge rectifier or equivalent to allow for swapped pairs. The delay might be due to the PoE power negotiation. \$\endgroup\$
    – Kartman
    Commented Jun 10, 2022 at 6:10

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  1. The delay may come from the device itself. As @Kartman pointed out in their comment, the power negotiation may take time.

  2. POE (802.3af or 802.3at) 48V is a floating (i.e. isolated) voltage. So there's no ground reference. From what I understand from your schematic VCC_48V_POS is referenced to VCC_48V_NEG.

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