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TPS54560B-Q1: TPS54560B inductor squeaking

Sammi Shang
Expert 4450 points
Part Number: TPS54560B-Q1
Other Parts Discussed in Thread: TPS54560B

Dear team,

Customer use TPS54560B in their design, Vin=12V, Vout=5V, Iout=4A. Customer found the inductor squeaking when Iout=4A. The sat current of  inductor they used is 8A. Seems not exceed. I also attached the schematic and PCB, hope you could help review it.

Thanks.

Best regards,

Sammi

  • 0
    TI__Mastermind 25590 points

    Sammi,

    Audible noise from the inductor is probably caused by SW node instability. Please confirm by sharing SW waveforms in this condition.

    Does this occur with the 4VOUT circuit as well? Have they test stability criteria (bode plot, load step response) for these circuits? I recommend they check the compensation values using section 7.3.14 in the datasheet.

    -Sam

  • 0 in reply to Samuel Jaffe
    TI__Expert 4450 points

    Hi Sam,

    Thanks for your response.

    The inductor noise happened when load@>300mA, currently IC will enter into DCM mode. The output voltage and ripple voltage are both perform well for customer. So now:

    1. I wonder if the inductor 1uH is too small for this 2.4MHz application?

    2. I calculated the COMP, that according to customer's COMP network, the cross-over frequency is only 12KHz, I am not sure but think this is too small for a 2.4MHz application. But the output voltage and response now are OK for customer.

    Hope you could give some suggestion.

    Thanks.

    Best regards,

    Sammi

  • 0 in reply to Samuel Jaffe
    TI__Expert 4450 points

    Hi Sam,

    Customer has modified the noise through change the frequency to 1.8MHz, and inductor to 4.7uH.

    With the new parameters, the noise decreased and the SW waveform became normal. But when startup, customer still could heard some noise.  I calculated the COMP with the guide of datasheet and Fco=40KHz, R4=26.3K, C5=4.7nF, C8=6.7pF.

    I still have question about the cross over frequency, because in my mind, the cross over frequency should be 1/10 of switch frequency. So could you help confirm this? Or could you help simulate the loop stability?

    Thanks.

    Best regards,

    Sammi

  • 0 in reply to Sammi Shang
    TI__Mastermind 25590 points

    Sammi,

    1. 12VIN to 5VOUT at 2.4MHz at ~90% efficiency gives inductor ripple of ~1.4Apeak-peak. You may want to consider a higher value inductor.

    2. 12kHz crossover is slow but would not be the cause of instability directly. Check the phase margin. Fco of 1/10 of FSW is the recommended max crossover frequency. Higher frequency gives faster response which is desired but it should not be the cause of instability.

    Take a look at the switch waveform while the audible noise is happening. Does it look normal? Can you share waveforms?

    -Sam