Grounding Issue in POE circuit

[vikaskumar1983]

Hi

I have designed a POE circuit in my project. But after testing that Hardware I found the if you connect BNC connector with that board the POE circuit shuts-off.

Board is having 3 types of power input facility:

12V DC input

24V AC input which is going to POE circuit and is converted into 12V DC

48V POE input through RJ45 connector. This voltage is again converted into 12V DC.

We have one BNC connector to take the video output. When the cicuit is operated with 48V POE input, 12V DC is generated which is perfect, but when I connect the BNC cable which is connected to TV then after 2-3 seconds the Circuit switched.
I have used some EMI filter arrangement also in the circuit. I am not able to locate the problem that who is making the circuit off.
I am attaching the Circuit, If somebody can help me here, I will be very thankful.

Best Regards
VK

 

[arikp]

Hi ,

Did you find out what was wrong in your design ?

Thanks ,

Arik P.

 

[ronak shah]

Hi vikaskumar,

Hope you have solved "Grounding Issue in POE circuit".

We have successfully made IEEE 802.3at enabled POE device as per TI tps23756EVM as described in below figure.
Issue We are facing is:
As IEEE 802.3at enabled PSE device needs proper start-up state mechanism as per IEEE standard. I think we are not able to go into the classification stage of the initialization.
But when we connect oscilloscope's probe(earthed with ground) to VDD, device goes into classification and normal operation. And PD successfully get 54 voltage from PSE.

So pl. let me know what is the solution for POE bring-up!!! Your help will be appreciable!!!

Thanks,
RNK.