• State TI Thinks Resolved
  • Locked Locked
  • Replies 11 replies
  • Answers 3 answers
  • Subscribers 64 subscribers
  • Views 1879 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TPS61193-Q1: output capacitor has terrible audible noise

Jiang Boqian
Intellectual 655 points
Part Number: TPS61193-Q1
Other Parts Discussed in Thread: TPS61193

Hi TI team,

As expected, by using PWM dimming product TPS61193, we can hear terrible audible noise, I have uploaded my SCH, can you help to have a look?

From my understanding, the audible noise is coming from PWM dimming's highest and lowest output current, during high current Vout is smaller, during low current Vout is higher. This will make ceramic output capacitor audible.

And this noise is not caused by output ripple voltage when the boost converter's inductor is charging, right? So adding output capacitance is not helping.

What can I do?

Thank you and have a nice holiday...

  • 0
    TI__Genius 15776 points

    Hi

    First could you help me to make sure the source of noise.

    You can remove some cap or replace  ceramic cap to electricity cap to make sure the source.

    Second.could you offer the issue schematically

  • 0 in reply to Frank Qiu
    Prodigy 100 points

    Hello, we measured the approximate position with a microphone. The decibel of the sound at the inductor is about 55dB, and the decibel of the output capacitor is about 62dB. It should be the howling sound from the ceramic capacitor.
    Electrolytic capacitors are a bit bulky and too high in height. At present, we have increased the PWM frequency to 15KHz, and howling has been greatly improved, but it is described in your document that it will affect the linearity of dimming. Is there any other way. Thank you！

  • 0 in reply to lfcchen
    TI__Genius 15776 points

    Hi 

    Another way to solve this issue is to use electrolytic capacitor.

    The nosie is based on the caremic cap‘s structure.So if you don't want to increase you should use electrolytic cap.

  • 0 in reply to Frank Qiu
    Prodigy 100 points

    Hi，Frank：

           The electrolytic capacitor occupies too much area on the PCB, and the height is too high, and the structure is unacceptable. Is there any other solution?

    Howling noise is almost inaudible when the PWM frequency is increased, but TI's document writes that it will affect the linearity of dimming. Can you specifically

    talk about the consequences of affecting the linearity of dimming?

          Thank you！

  • 0 in reply to lfcchen
    TI__Genius 15776 points

    Hi 

    To solve the noise of cap you have two ways

    1) to increse the frequency

    2)use electrolytic or Tantalum capacitor tp replace the ceramic cap.

    So you can choose Tantalum cap as another solution.

    About the linearity of dimming :

    I want to ask a question first, what's the dimming retio you need and what's the request of your linerity.

    You can regared the dimming as the ratio of actual current to maximum current. And there is a FET to control the output current, So you can also regard it as the duty cycle of PWM.The FET has minimum conduct time and control circuit has the minimum change time.So when the frequency is low the duty cycle of the FET change linear.

    For example, the mimimum conduct time is 200ns and the minimum change time is also 200ns,when the frequecny is 1kHz,you can get the duty cycle as  0.002% 0.004%....and when the frequency is 100k the D will be 0.2% 0.4 .....




  • 0 in reply to Frank Qiu
    Prodigy 100 points

    Hi，Frank：

           We currently do not have a test for dimmability, and there are no standards for linearity.

    So I would like to consult you, if I increase the PWM frequency and affect the light linearity, what can I do to correct it? Thank you!

  • 0 in reply to lfcchen
    TI__Genius 15776 points

    Hi

    Sorry, i don't get what you what to do, if there are no standards for linearity why do you waht to correct?

  • 0 in reply to Frank Qiu
    Prodigy 100 points

    Hi，Frank：

         1. Is it necessary to replace all ceramic capacitors with tantalum capacitors?

         2. Our customers have no requirements for dimming, but we saw this in TI's documents, so we want to know what kind of negative effect of increasing the PWM frequency on dimming？

    Thanks！

    chen.huan

    13632994598

  • 0 in reply to lfcchen
    TI__Genius 15776 points

    1. Is it necessary to replace all ceramic capacitors with tantalum capacitors?

    A：Just replace the cap which generate noise.

     2. Our customers have no requirements for dimming, but we saw this in TI's documents, so we want to know what kind of negative effect of increasing the PWM frequency on dimming？

    A:You can regard it as decrease of dimming ratio.

  • 0 in reply to Frank Qiu
    Prodigy 100 points

    1. Is it necessary to replace all ceramic capacitors with tantalum capacitors?

    A：Just replace the cap which generate noise.

    Reply：The values in the picture are the measured sound decibels of each device. When the 10uF capacitors are replaced with tantalum capacitors,

    the howling sound is reduced, but it still exists.

    2. Our customers have no requirements for dimming, but we saw this in TI's documents, so we want to know what kind of negative effect of increasing the PWM frequency on dimming？

    A:You can regard it as decrease of dimming ratio.

    Reply：Will the subjective feelings have a great impact, causing visual discomfort？

  • 0 in reply to lfcchen
    TI__Genius 15776 points

    1.Replace the cap which generate noise

    2.no