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LMR23630-Q1: About Switching voltage noise

GARAM AN
Intellectual 1950 points
Part Number: LMR23630-Q1
Other Parts Discussed in Thread: LMR23630

Hi all,

The FB path layout goes near inductor, so I know that this noise and spikes came from the FB noise.

I know that FB noise makes a lot of problem on the stable output, but I cannot understand how the FB noise makes switching voltage ringing and unstable output voltage

Could you please explain with picture? 

Thank you

This is when load is 2A with LMR23630, condition is Vin=12, Vout=3.3v, Iout=1.5A.

  • 0
    TI__Expert 4555 points

    Hello Garam,

    SW voltage ringing is not instability. 

    You are seeing SW ringing because your part is configured for PFM mode, and this mode doesn't allow inductor current to go negative to increases light load efficiency. That is why when your inductor current ramped down to zero, SW gets tri-stated (both high and low side FET turned off) and the ringing you are seeing on the SW is absolutely expected and you are only simply seeing resonant oscillation between SW capacitance and output Inductor.

    In conclusion, I would say the phenomenon you are seeing is absolutely expected and doesn't show any hint of instability.

    Hope this helps!

    Please let me know if you have more questions.

    And if you think your question has been answered, please close the thread. Thanks!

    Best Regards,

    Ankit Gupta

    Application Engineer