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Ringing on SW pin, how to analyze it and how to deal with it?

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Dear all,

For the Ringing on SW pin(a Buck DC-DC, CCM mode), how to analyze it and how to deal with it?

At system-level, maybe we will Immediately think of adding R and C...

How to analyze it(which factors involved) and how to eliminate in chip design?

Having no idea...

Thank you in advance.
333.JPG
 

That looks like very HF noise and it's not ringing per se
because it doesn't decay. The edge overshoot may just
be an artifact of the output switch kicking the ground
that you're referred to.

Be aware that adding capacitance (probe) to the SW node
will add to the observed noise / overshoot as-displayed.
Use a series resistor with your probe tip (such that the
RC w/ probe capacitance is still > BW of interest) and see
how much the picture improves. 1K series is 100MHz BW
and a 0.1% gain error on a 1Mohm / 10pF probe.
 

That ringing doesn't look too severe, but it's hard to tell without a faster timescale to look at.

You should look at this thread which has a lot of discussion on dampening ringing:
https://www.edaboard.com/threads/243100/
 

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