TPS23754: TPS23754PWP EMI/RE Noise Issue

Hi Darwin thanks for your support

Till now we have done some changes.

We have increased the value of R201 to 72E and below observations are made

•  At low load(consumption in mA) - noise level is comparatively less
• At 12V@1A- noise level increases at the output side.

Also we tried by adding a snubber across MOSFET C=330pf, R=10E &C515, C516, C517, C518=1000pf. But still getting noise at Output and near MOSFET. 

Please suggest what can we do to reduce the Noise. 

Attached are the screenshots for your reference. 

Hi Ravi,

I'm not sure what you mean by noise near the FET and output. Yes the switching elements will radiate noise; however, radiated noise from a standards point of view is radiation of the ethernet cable when connected. The idea is that end equipment itself is not radiating since majority will have a shield enclosure or shielded coating of the end product. Whatever noise in the end product is radiated to the RJ45 input and that noise will radiate from the ethernet cable. Is your end product enclosed during your testing and also is the enclosure shielded? 

Hi Darwin

yes, the product is enclosed during testing. we got the results of our RE and CE and the results are worse. please see attached file. please suggest how we can approve0730-ISN.pdf0729-RE.pdf

Hi Ravi,

If you are failing CE as well can you try adding a common mode choke in series with their ferrite bead. Youcan also try unpopulating C702 and R705 to remove the common mode current.

Otherwise, we have to look at the layout as well as this can cause EMI issues.

Hi Darwin

We have also tried by adding common mode choke in series and by removing C702 and R705. But still results are same

Hi Ravi,

This is very surprising. Either the layout is bypassing the common mode choke, or there is component that we are missing that is on the board but not on the schematic(although I only got the poe schematic and the full board schematic). Can you forward this? If it not a component then it must be layout or possibly setup. Can you also send how you're taking the measurement?

Ravi, It has been over a week since there was activity on this thread.

Do you still require our help?

Thanks,