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LM61495: Audible Noise form DC/DC Converter, DC/DC Converter

LP Kim
Intellectual 510 points
Part Number: LM61495
Other Parts Discussed in Thread: DLPA3005

Tool/software:

Dear 

Most likely, of course, the inductor is noisy. 

I am using the schematic provided by TI and am also using the same inductor.

Any noise in the audio range is highly undesirable.

Tell me what to change to minimize it such as PCB design, Components and inductors.

Thanks

(TI Rerence Schematic)LM61495_VOUT19V_IOUN10A.pdfLM61495_PCB DESING.pptxLP61495RPH.pdf

  • 0
    TI__Genius 11495 points

    Hi,

    What are the operating conditions under which you are seeing the audible noise? 

    Can you check the output voltage ripple and the inductor current and share with me?

    Thanks,

    Best Regards,

    Taru

  • 0 in reply to Taru Kapoor
    Intellectual 510 points

    Hi 

    Thank you for youre reply. 

    What are the operating conditions under which you are seeing the audible noise? 

    [250422-LP]  There is no noise when there is no load, but even a light load causes audible noise.

    Can you check the output voltage ripple and the inductor current and share with me?

    [250422-LP]

    Please refer to real measuremnet result related to output voltage ripple. 

    Does 'inductor current' refer to the actual measured current? I'm currently using the inductor recommended by TI.

    The DC/DC converter is connected to the main power input of the DLPA3005. The LED current is in the range of 1 to 10 A.

    Power supply: 24V / 3.5A → DC/DC: 19V → DLPA3005 input: 19V → DLPC LED Setting : 10A.

    Can I solve the audible noise after chaing switcing frequency? 

    Thanks

    Best Regards 

    LP KIM

  • 0 in reply to LP Kim
    TI__Genius 11495 points

    Hi LP,

    I'll review this and get back to you by EOD. 

    Thanks,

    Best Regards,

    Taru

  • 0 in reply to Taru Kapoor
    TI__Genius 11495 points

    Hi LP,

    Few comments/ requests:

    1. I checked the inductor waveform - based on what you have shared - the time difference between two swithcing instances is ~15us - which leads to a frequency of ~67kHz which is well outside the audible range. 

    2. Are you sure it is the inductor causing the noise? Ceramic caps can also cause audible noise because of their piezoelectric effect. (See https://www.murata.com/en-sg/support/faqs/capacitor/ceramiccapacitor/char/0020). Please confirm.

    3. Can you change the mode to FPWM and check if this solves the issue? 

    Thanks,

    Best Regards,

    Taru

  • 0 in reply to Taru Kapoor
    Intellectual 510 points

    Hi Taru 

    1. I checked the inductor waveform - based on what you have shared - the time difference between two swithcing instances is ~15us - which leads to a frequency of ~67kHz which is well outside the audible range.

    [250424- KES] I known that the switching frequecy measured aging . it was about 400[kz]. As you mentioned , it was outside the audible range. 
                            I think that the root cause isn't not inductor with 400KHz frequency. What do you think? 

    2. I will check. 

    3. Impossible.

    Thanks 

    Best Regards 

  • 0 in reply to LP Kim
    TI__Genius 11495 points
    LP Kim said:
    I known that the switching frequecy measured aging . it was about 400[kz]. As you mentioned , it was outside the audible range. 
                            I think that the root cause isn't not inductor with 400KHz frequency. What do you think?

    I am not sure what you mean by this. But yes, as I said - inductor doesn't seem to be the problem based on what I can see. 

    Can you also check if the inductor is mounted and soldered firmly on the board? 

    LP Kim said:
    2. I will check. 

    I shall wait for your response. 

    LP Kim said:

    3. Impossible.

    I am not asking you to change the design permanently - this is just to troubleshoot. 

    Thanks,

    Best Regards,

    Taru