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TPS63030: ringing tones from output capacitors in power-save mode (under 100mA output current)

Nate Ferris
Prodigy 10 points
Part Number: TPS63030

Hello,

I am using the TPS63030DSKR component to boost from 4.9V to 5.25V, with output current 3mA-40mA depending on the load. I followed the reference design for both schematic & layout, as of this moment I can hear ringing tones at 8kHz and 16kHz when the device is on and operating. I am tying PS/SYNC to ground in to use "Power Save" mode, I noticed that the reference design has generic  2 x 10uF caps in parallel on the output of the regulator. I am using two ceramic caps, which I calculated to resonant at ~8kHz (10uF) and ~16kHz (20uF).

Looking back at the datasheet, there is no mention of specific part numbers for the two caps, nor advise on cap size vs. output current. I am realizing this part is geared towards ~100mA applications, and I am far below that. My solution right now was to swap out the 2 x 10uF ceramic caps to tantalum caps, this makes the ringing go away. However, I am wondering if I even need 2 x 10uF caps for my low current application? (perhaps a single 1uF cap will suffice). Any input appreciated, thanks!

  • 0
    TI__Guru 58225 points

    Hello Nale,

    The device is internally compensated and the output capacitors influence the pole frequency of the converter. You might check if the device is still stable when you increase the inductor value at the same rate as you reduce the capacitor value.

    In general using capacitors in a smaller package reduces the likelihood of hearing a sound.

    Best regards,
    Brigitte

  • 0 in reply to Brigitte
    Prodigy 10 points

    Hey Brigitte,

    Thanks for the fast reply. I currently use 0805 components, smaller packages such as 0603 or 0402 should mitigate this issue?
    I tried 2 x 1uF capacitors and saw stable output voltage, low ripple, and efficiency about the same as the 2 x 10uF setup. This simply pushed the tones higher beyond what a human can hear, which does resolve this issue for me. Would sizing down to 1uF require the inductor to increase? How much does output current affect the sizing of these components?

    I'm leaning towards using 2 x 1uF, but I don't want to simply size down to 1uF without knowing trade-offs / consequences of my decision, what are your thoughts on this? 

  • 0 in reply to Nate Ferris
    TI__Guru 58225 points

    Hello Nate,

    Please do a load transient to check for stability with the reduced output capacitors, see here: ti.com/lit/an/slva381b/slva381b.pdf

    The stability is the problem that I could imagine if you reduce the output capacitance below the recommended value.