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LMZ10505 - Audible Noise

Patrick Dietrich
Prodigy 40 points
Other Parts Discussed in Thread: LMZ10505

Hi There,

We've used the LMZ10505 on many designs now with no issues.  However recently our manufacturing department has reported several boards that have a high pitched audible noise when under load during testing.  What typically causes this type of behaviour?  And what can be done to fix the issue?

+VIN is +5V and, my output is +3.3V

Thanks,

Patrick

Below our some captures, of my sch and pcb layout for the part:

  • 0
    TI__Genius 11085 points

    Hi Patrick,

    Thank you for the detailed information in the post. The schematic, compensation and layout look good.

    What is the failure rate?

    The LMZ10505 operates in CCM at all load conditions. There is no frequency shift in operation. The high pitch audible noise sounds like instability to me. If the problem still exist after making sure every passive component is soldered on correctly, I'd replace the input capacitor with a bigger cap. It could be that some ceramic caps derate more than others, thus Vin is not sufficiently bypassed. When Vin bypass is not enough, the switching noise could interfere with the control loop and cause instability in some conditions. Let me know if this helps.

    Regards,

    Yang

  • 0 in reply to YangZhang
    Prodigy 40 points

    Thanks for giving us some direction to look at.  We've solved the problem now!

    We had the rcomp value specified at 953ohm, but this batch of boards were assembled incorrectly with 963k ohm!!!  So I guess this would cause some instability problems.  Anyways we've changed the part to the proper value and all is good!

    Thanks again for your help!