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LM25145: Audible noise from inductor

Vanker Priyanka
Prodigy 110 points
Part Number: LM25145

Hi

In our design LM25145 IC is used for 5V/9A. At no-load condition inductor generates some Audible Noise, we use the same circuit that design in web bench. I don't Understand Why inductor generates Audible noise?

To remove this noise which are the steps I can follow?

Please Find attached web bench design for LM25145 IC.

Thanks & Regards.

WBDesign114.pdf

  • 0
    TI__Mastermind 23845 points

    Hi,

    Is the output oscillating? What is your output voltage waveform looks like?

    Thanks

    -Arief

  • 0 in reply to Arief Hernadi
    Prodigy 110 points

    Hi

    In output waveform, Buck converter generates one 5.2V DC line but at the same time inductor generates noise at no load condition while saturation current of inductor is 12A then why inductor generates noise?

    Please find attached copy of output waveform.

    Thanks & Regards.

  • 0 in reply to Vanker Priyanka
    TI__Guru 66602 points

    Hi Vanker,

    This is likely related to diode emulation mode that's selected via the low state at the DEMB/SYNCIN pin (as it results in frequency foldback at light loads). Tie DEMB/SYNCIN to VCC to enable forced PWM (FPWM) mode operation for constant switching frequency across the full load range.

    Regards,

    Tim 

  • 0 in reply to Timothy Hegarty
    Prodigy 110 points

    Hi

    The SYNCIN pin is already connected with VCC but inductor generates noise at no load and when the load is connected about 5A at that time noise in inductor increasing then what should I do to prevent audible noise in the inductor.

    Thanks & Regards.

  • 0 in reply to Vanker Priyanka
    TI__Guru 66602 points

    Hi Vanker,

    Please check that the SW node voltage is stable at the chosen switching frequency for the load conditions where the audible noise occurs.

    I recommend completing the LM25145 quickstart calculator (the file can be downloaded from the product folder under "Design and Development") to check compensation values and bode plot. Also, a shielded inductor will help.

    Regards,

    Tim

  • 0 in reply to Timothy Hegarty
    Prodigy 110 points

    Hi

    I am using the same inductor which is recommended in web bench design in which inductor is shielded type and at SW node side the switching frequency will be 353.4 kHz at no load condition but at the same time inductor produces Acoustic noise so, what should I do to remove inductor noise. The Inductor part num is PA5005.332NLT

    Please Find the Attached image of SW node at no-load condition.

     Thanks & Regards.

  • 0 in reply to Vanker Priyanka
    TI__Guru 66602 points

    Hi Vanker,

    This SW node waveform indicates instability. Please see attached completed LM25145 quickstart file for this design.

    I recommend increasing both the input capacitance (to 10uF/50V/1210) and the output cap (to 47uF/10V/1210). These values should be derated by 30% to 50% in the quickstart file as ceramic capacitance derates with applied DC voltage. Then install the compensation component values recommended in the file to stabilize the design. Also, I noted the current limit is set somewhat high. You can adjust Rilim and Cilim if needed.

    Finally, I will notify the WEBENCH team to correct the recommended values for these design specs.

    LM5145 Wide Vin Synchronous Buck Controller Quickstart Calculator r12-7 -- 9-36Vin 5V 9Aout 350kHz.xlsm

    Regards,

    Tim

  • 0 in reply to Timothy Hegarty
    Prodigy 110 points

    Hi

    I am changing the input capacitor, output capacitor Rlim and Clim but there is no effect on inductor's noise so can you please guide me what can I do to remove audible noise

    Thanks & Regards.

  • 0 in reply to Vanker Priyanka
    TI__Guru 66602 points

    Vanker,

    Check stability - and use the quickstart calculator to derive compensation component values.

    Regards,

    Tim