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UCC28782: A ringing sound occurs

TETSU
Prodigy 250 points
Part Number: UCC28782

Hello TI-Team,

Dithering is enabled and a abnormal noise sounds when the load becomes heavy.
The abnormal noise sounds seems to be coming from the input/output ceramic capacitors.
Please tell me why the tones occur even though the loop gain is fine (no oscillation).
It seems to be related to the ZVS tuning, but the oscillation frequency is 150~160 kHz.

Also, please tell me how to counteract the problem.

Kind regards

TETSU

  • 0
    TI__Mastermind 26830 points

    Hello Tetsu-san, 

    Please provide more information about your application and the operating conditions when the noise occurs. 
    What is the input voltage range and the maximum output power and voltage?  
    Is your circuit using Primary Resonance or Secondary Resonance?

    Audible noise from ceramic capacitors comes from large changes in voltage at less than 20kHz. 
    Is it possible to acquire waveforms of the voltage across the caps from which the noise originates?
    Please identify where in the circuit the noisy capacitors are located.  

    Dithering of the switching frequency is enabled at higher loads and higher input voltage. Its frequency is at 23kHz, so it should not be audible. 
    However, if there is another frequency within ~20kHz of the dithering, there may be an audible beat frequency between the two. 
    Does the noise still happen when the input voltage is very low (when dithering is disabled)?

    Regards,
    Ulrich

  • +1 in reply to Ulrich Goerke
    Prodigy 250 points

    Hello Ulrich,

    I would like to communicate via email as it contains design information.

    Could you share your mailing list?

    Tetsu