TPS23861: Automatic mode not showing any activity; cannot communicate with IC via i2c

Hi Gage,

How about the port voltage? It should show an open circuit voltage like shown in the datasheet.

The schematic looks correct to me. Do you have the rest of the schematic as well with the data transformer and RJ45? Thanks!

Hi Darwin,

I measure a constant 48V across the port, I don't see any waveform like the datasheet shows on a scope.

Hi Darwin,

I measure a constant 48V across the port, I don't see any waveform like the datasheet shows on a scope.

Hi Gage, sorry for the delay here. 48V on the output port (Pair 1/2 3/6) of the PSE means the port is always ON. Is the external FETs shorted?

Looking at the extra schematics you attached, the IO_1_GND shorts to GND catch my eye. Can you remove all the 0 ohm shorts and capacitor connections between these two nodes? 

Hi Darwin,

I've checked the FETs on several boards, there are no apparent shorts. I've tried taking off the FETs to see if I can even communicate to the IC via i2c but I cannot get any response.

I also tried removing the 0 ohm resistors and capacitors on the main board as you suggested...no change. To give some context, there is a main board with a Switch IC and the RJ45 connectors; the PoE IC is on a daughterboard that contains the 48V power supply and the PoE IC. If you can open Altium files I can send you the board projects offline -- maybe there is something I am missing on the PCB itself.

Thanks!

Gage

Hi Gage,

Yeah the schematic looks good to me so PCB would be next. Yes I can open Altium files. Please go ahead and send me the project .zip and we can review. Thanks!

I might be missing something, but I don't see how to privately send the .zip files. Could you send me an email or give me an email address to send the .zip files to?

Thanks!

Hi Gage, I have sent a private message and we can continue this offline. Thanks!