I have a custom board which is powered by Ethernet and I am using the LT4275B from Linear using the recommended schematic.
When I am using a cable with only the data pairs [1-2]&[3-6] ([4-5]&[7-8] are disconnected), I can plug as many of my boards I want and I have no problem.
But now, if I use a complete cable with the four pairs connected I have this problem : If I plug a board I can see in the web page of the PoE switch the Class of my board and the consumption. Now I plug a second board (which is the same hardware) BUT I can't see my board, neither the Class nor the consumption. The switch consider the consumption of the second as if it was the one from the first board.
So for example I have two boards with 2W of power consumption, if a plug one board I have 2W on the first board. Then I plug the second board and I have 4W for the first one and 0W for the second one. And so on (6W for three, etc.).
I have this problem on all the PoE switch I had in my hand (Sisco, HP, and more).
Do you have any ideas ? Is it possible that the problem come from my RMII chip (DM9161A) ?
Thank you for your help !
When we cut the spar pairs it works properly as well when we use Ethernet Crossover cables... Strange...