TPS63021: EMI issue with peak radiation observed at 318MHz

Hi Navya:

The image is lost. May you upload them again? Thank you! 

Sorry, I can see them now.. I'll reply soon..

Hi Navya:

The peak radiation issue may cause by the layout. May you share other layer? And do you catches the waveform of Switching? at the L1, L2. 

Hi Minqiu,

Appreciate your quick response.

Yes, please find the attached images for waveforms probed at L1 and L2 and PCB Layout.

1) To isolate the issue, we cut the shape in the PCB at the input of the regulator and supplied 5V Vin externally. However, we were still able to see the radiation closer to the regulator circuit (predominantly at the input). 

2) Also, we isolated the output of the regulator and connected to another 3.3V resistive load and observed the radiation at 318MHz to 324MHz.

3) Regulator circuit does not radiate when the output is not connected to any load.

4) Is it possible to vary the switching frequency of TPS63021?

Appreciate your response at the earliest.

Warm Regards,

Navya

Hi Navya:

I afraid it may cause by the parasitic parameters. If you check the L1 waveform carefully, you will find there are ringings at the rising and falling edge. (Interesting thing is the L2 is clean..)

Can you soldering additional 0603 1uF as close as possible to the IC, and minimum the loop of  Vin-GND and Vout-GND? Just for layout checking. 

And here is a application note about the layout. www.ti.com.cn/.../slvaep5.pdf

And another for adding a snubber circuit .www.ti.com.cn/.../slva255.pdf

Hi Navya:

Is there any update?