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LM5175: Inductive whistle under light load condition

Jianing Zhu
Expert 4325 points
Part Number: LM5175

Design parameter：Vin=24V， Vout=12V/7A

The filter inductance value is 4.7uH(20A)

The problem is : While under light load condition, the inductor would whistle.

Following is the waveform under no-load condition:

       

Fig.1.waveform of mosfet                                                                                 Fig.2.waveform of output voltage ripple

What could cause this phenomenon?

Thank you.

  • +1
    TI__Guru 66390 points

    Hello Jianing,

    There are several possible reasons for acoustic noise in the system.

    Can you please check the frequency of the load signal while in light load? It is possible that this is the root cause for the noise created by some components.

    Please check the output voltage for lower frequency oscillation as acoustic frequency is below 20 kHz.

    Please check as well if the noise is gone when you remove the inductor from the board and connect it via short wires. This decouples the inductor oscillation from the board.

    Please take measurements of both switch nodes for a longer period of time.

    Best regards,
    Brigitte

  • +1 in reply to Brigitte
    TI__Guru 66390 points

    Hello Jianing,

    As I did not hear back from you, I expect you have been able to solve the acoustic noise issue and I will close the thread now. If this is not the case, please post below or create a new thread if this on is already locked.

    Best regards,
    Brigitte