Audible noise from 5V Regulator

I just made 5 PCB’s with MPS’s DC-DC regulator MPM3550EGLE. All 5 have a high frequency whistle. It starts at 14.9Khz and then drops to 13.5Khz after a minute or two and is then stable. I don’t remember having this issue on other boards, but I was not looking for it. Any ideas what this could be? I don’t know how to tell if it is the chip itself or one of the caps around it. All the caps are ceramic.

Hello olearyds,

Welcome to the DigiKey TechForum.
I’m not familiar with this issue, but hopefully one of the engineers may have an idea, and can help with this.

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What Input and Output Capacitor values/voltages are you using?
It could be helpful also to provide the part numbers for the caps to look at ripple current ratings.

Have you poked an oscilloscope probe on any of your components to see if the frequency is visible on that part?

Do you have an input filter inductor for EMI considerations?

It couldn’t hurt to provide the layout of your circuit board to see if anything stands out if that’s available.

One of our Applications Engineers David_1528 dug up some Application Notes from the capacitor manufacturer Murata indicating ceramic capacitors can be a source of noise given the right circumstances.

Application Notes Linked Below:

MLCC solutions for suppressing acoustic noise in the battery lines of laptop computers


Ceramic Capacitor FAQ - Why does acoustic noise occur in ceramic capacitors, and does this have any effect on reliability?

Murata has some capacitor series available that cut down on this noise like the ZRB Series

The input is 20V, although I had the input at 4.7V and heard the same sound.
C12: GRM188R6YA225MA12D
C13/14: 08053D226MAT2A
C51: GRM155R71H104KE14D
I have not looked at the output on a scope but will do so and report back.

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Yes, you can see it on a scope. This is at 14.8Khz, but I did not have it on very long.

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Looks a lot like the sample waveform on p9 of the datasheet.

Cycle skipping under no/low load conditions can end up seeing ripple voltage in the audible spectrum, which as mentioned can be transformed into noise. Put a load on it, and I expect the noise will go away.