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TPS53353 ringing

Tom Saluzzo
Expert 1280 points
Other Parts Discussed in Thread: TPS53353

I am using the TI TPS53353 on my board (3 of them actually) and they all have this switching node ringing I would like to remove.
 
Here is the schematic page and also the SwitcherPro design report. I think we followed the design pretty close. Shouldn't the snubber circuit clean up the peaks and ringing?
 
I found some app notes on line (TI included) and tried to experiment with some cap and res values but nothing is making much difference. Is there something else I should be looking at?

sch.docx0p9V_RegDesign.pdf

  • 0
    TI__Guru**** 191445 points

    Usually the best approach is to add an RC snubber from the switch node (LL) to GND.

  • 0 in reply to JohnTucker
    TI__Guru**** 191445 points

    Since they are already using the BOOT resistor and snubber, they may need to fine tune them. While they are not the exact values as recommended by switcherpro, they are close enough. I would be willing to bet that the RC snubber and BOOT resistor values are not calculated by switcherpro, but instead just standard plug in constant values. While I have not worked directly with TPS53353 (it is HPS not SWIFT), for other integrated FET devices a BOOT resistor value between 5 and 25 ohms may be more effective. The RC snubber values are dependent upon the layout. You can optimize the snubber using the enclosed procedure. Of non of those work, then we will have to look at the layout. It some cases it may not be possible to completely eliminate the ringing on the SW node. Then the next remedy is to filter the artifacts off the output voltage rail (which I’m sure is the real concern here). The 100uF output capacitors will have resonant frequency below the ringing frequency. You will need to add some other lower value bypass resistors in parallel. 1.0uF, 0.1uF, 0.01uF, etc. the net effect is to have a broad frequency band with low impedance to ground. You could also consider a ferrite bead on the output.

    RC Snubber.doc