TPS23753A: TPS23753APW

Hi Brijesh,

PoE team is doing internal tests and the reply on E2E may be delayed for 3 - 5 business days. Sorry for the delay and thanks for your patience.

Best regards,

Diang

Hi Brijesh,

Thanks for your patience. Most of PoE EVM does not go through EMI test. There could be one/two ran the EMI and have the results in application note.

Designing an EMI Compliant PoE with Isolated Flyback: www.ti.com/.../slua469.pdf

 Best regards,

Diang

Hi Diang,

The app note  you shared does not have CE test details with 24VAC input section because we are failing on the 24VAC input but not on POE input, on POE input our CE is already passed. 

in TI EVK CE is not tested with 24VAC input? 

Please help me how we can pass CE on 24VAC input?

Thank you

Brijesh K

Hi Diang,

we have also performed the CE testing with POE input and in that as well we are failing on the High frequency side.

We have tested 3 different devices with POE input but they are having same POE circuit which is shared as below. In all 3 devices we are failing on the High frequency side, Graphs of all 3 devices are attached please check and can you please let me know what can be reason for the failure and what can be the solution?

CE_Issue.zip

Hi Brijesh,

Solder the these two decoupling capacitors to compensate the switching transient.

Considering the Q1 is a very small die FET with 700mOhm on resistance, you can further increase the R14 to 100 Ohm. It is also optional to add the snubber R17 and C37. Or you may consider using a FET with 100 - 200 mOhm on resistance.

If above changes do not help, you can consider to further add Y-caps.

Best regards,

Diang

Hi Diang,

We have done all the suggested reworks into POE section and below are results so can you please check and  suggest us what we can do further?

Hi Brijesh,

Thanks for your updates. I will look through and get back to you in 3-7 business days. 

Best regards,

Diang

Urgent !

Hi Diang,

Can you please suggest me solution for this 24VAC circuit, how we can solve the conducted emission ? Can you please suggest me modification required in 24VAC circuit?

This is stuck since long time and we have not heard from you for this 24VAC we have to solve it urgently

Thank you

Brijesh K

Hi Brijesh,

Can you let me know which MOSFET at Q1 you are using now? 

 If the issue only happens with 24VAC case? It means your voltage at adapter after rectifier is 24V * sqrt(2) = ~34V? 

You may try change R16 to 50k or 75k to set fsw = 200k or 300k see if get better results

Check below link for more information

https://www.ti.com/lit/an/slua469/slua469.pdf

Best regards,

Diang

Hi Diang,

We are using AM3490N-T1-PF Mosfet. The conducted emission failure happens with both the input cases (with 24VAC Input & POE Input as well). 

Hi Brijesh,

Thanks for your reply. 

Could you share the datasheet of AM3490N-T1-PF if it is not as below? 

As we discussed the Q1 is a very small die FET with 700mOhm on resistance, you can further increase the R14 to 100 Ohm. It is also optional to add the snubber R17 and C37. You better consider using a FET with 100 - 200 mOhm on resistance. Especially you have 24V * sqrt(2) = ~34V input which is lower than common PoE 37-57 Vin and with higher current. 

Best regards,

Diang