Problem with TPS23754

I have the converter circuit running now when I use a power supply to supply 40V from VDD to PGND.  However, when I try and use POE it does not start up at all now.  I tried to remove all loads from the 12V output but that did not help.

It came up once when I was trying to get the waveform but then every time I tried after that it woyuld not start up and I didn not see much of anything happening on Vdd or Vss.

I make the same design exactly as the -383 eval board & I'm facing the same issue as Michael Wilson described above even I'm using the Pulse transformer PA2649NL….

"when I try and power it on it never comes up. It acts like it is starting to and then reset. The duty cycle appears to be at a minimum and it seems to be resetting every time it switches to draw power from Vc"

Any idea about how you finally solve this issue?  

My board was fixed by:

1.  Moving the final output cap inside of my Diode.

2.  Grounding APD.

3.  Connecting the CLS resistor to VSS instead of GND

Thanks for the update, Michael.

Adam, if you suspect that your issue is different then please provide your schematics and pertinent waveforms and/or data.

Thx. Mike for you relpy.

Eric , at the biginig my board gives 12V duty cycle at Vout , now it's gives 0V ...
Attached is my  board sch as per your request.

Thanks

Adam. 

I forgot to mention that i performed my tests when JP2 is closed , means APD is connected to ARTN...

Adam, I see no issues with your schematic. Please provide additional information from the oscilloscope during start up. Provide start up waveform captures at VOUT and TPS23754 VC pin. Input and output load current during start up are also very useful.

Also provide a brief description of your test setup including where input power is applied (using PSE source to the RJ45/bridge or just some dc adapter applied between TPS23754 VDD and DGND net?) and the output load (load applied during start up or no load; resistive load or electronic load and if eload is it configured for constant current or CR?).