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LM5148: audible noise

user5054474
Intellectual 450 points
Part Number: LM5148

Tool/software:

Hi,

When the spread spectrum function of the LM5148 is turned on, audible noise is generated from the inductor and output capacitor.

Since the modulation frequency is 8.2kHz (min) and 16.2kHz (max), it is natural that the noise is audible, but is there any reason why the modulation frequency is set in the audible range?

Best regards,

  • 0
    TI__Mastermind 40040 points

    Hello,

    Its possible yo ucan hear the sp-sp.  Can you please measure switch node of the device when operting with a steady state load.

    Thanks.

    David.

  • 0 in reply to David Baba
    Intellectual 450 points

    Hi,

    What I would like to know is the background to why the spread spectrum frequency of the LM5148 is set in the audible range.

    When TI designs devices, does it take care to avoid entering the audible range?

    Best regards,

  • 0 in reply to user5054474
    TI__Mastermind 40040 points

    Hello,

    It has to do with the RBW of the EMI receiver, I am not saying this is the cause of your issue. we need to eliminate other possible more likely causes like instability.  I was merely answering your questions about the dithering frequency.  Please note we also implement dual random spread spectrum that helps with aduible noise.

    Please share your schematic with the calculator spreadsheet of your design, and scope shots of your switch node to determine the root cause of your audible noise.

    Thanks.

    David.