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TPS564208: Acoustical noise in Power supply

Daniel Hess
Prodigy 10 points
Part Number: TPS564208

Dear Support
We encountered some acoustical noise on our step down converter.
The frequency seems 14kHz but it seems hard to locate the error.

(Switching frequency is 560kHz)

The coil was soldered on 5cm cables and the noise is still on the PCB and also seems to be detectable on the coil?

Any idea where the frequency may came from?

Thank you-

Daniel

  • 0
    TI__Mastermind 30271 points

    Hi,

    Holly will help support this soon.

    BRs

    Lucia

  • 0
    TI__Expert 6425 points

    Hi Daniel, 

    The audio noise should be from output cap. Is output cap MLCC cap? 

    TPS564208 frequency is constant which is 560kHz. could you test SW and output voltage ripple waveform to double check? 

    BRs,

    Edwin. 

  • 0 in reply to Edwin Zang
    Prodigy 10 points

    I found a sample with very loud noise: The output CAP is MLCC 10uF but there are other MLCC and 220uF solid Aluminum cap in parallel. (12mR, low ESR). Total load capacity on rail is about 280uF.

    I calculated Pole frequency at about 5kHz and Noise is also around that (and multiples of 5kHz). 

    I found also deviations (much higher than ripple) of 300mVpp in output voltage rail with 5kHz freq. 

    We placed a capacitor to the feedback voltage devider to get fast response.

    This is C4 in the datasheet reference design. (Figure 14)

    When I remove this 33pF capacitor, the problem disappears accoustically and 5kHz deviations dissapear in output voltage. But I still need to have a fast response, so I cannot just remove the capacitor.

    • Could you help me with a formula/advice how to dimension this capacitor?

    Thank you in advance-

    Daniel

  • 0 in reply to Daniel Hess
    TI__Expert 6425 points

    Hi Daniel, 

    I'm confused about if C4 is in your board. You said that you placed C4 firstly, then remove it. Could you clarify it? Could you upload schematic to review? 

    BRs, 

    Edwin.