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DRV2700: VBST noise

Takumi Suzuki1
Mastermind 8430 points
Part Number: DRV2700

Hi,

I would like to ask you to give me your advice about following issues.

 - VBST noise 

   Will you tell me how to reduce the ripple noise of VBST?

   There is a not small ripple noise on VBST.

   I thinks that using a bigger "C(boost) value" seems to be one of the solutions. 

   There is 0.1uF as C(boost) on the EVM and do you know the upper limit of the value? 10uF?

   And if you know any other solutions to reduce the noise, please let me know.

One more question, please as below.

I know in case differential drive (OUT+/OUT-) woould be cancel the ripple noise.

But now I would like to drive a piezo with only OUT+ signal. (do not use OUT-)

In case of single drive, the ripple noise with OUT+ causes "noisy sound" from the piezo.

In my experiment, around 50V - 70V OUT+ causes bigger noisy sound than 90V out. (Vboost is 105V)

( around 50V - 70V is biggest, 20V and 90V are very smaller...)

I do not understand well why around 50V is bigger...will you tell me the reason?

Thank you for your support.

Best Regards,

  • 0
    Mastermind 8430 points

    Let me inform you about the L and REXT value as below.

    L is 4.7uH and REXT is 6.04Kohm as the same as EVM.

    And about "bigger noisy sound", in other words, bigger ripple noise.

    Thanks, 

  • +1 in reply to Takumi Suzuki1
    TI__Genius 17690 points

    Hello, 

    The ripple on the boost voltage can be limited by using a larger capacitor. Increasing the capacitor too much can make the boost voltage take longer to stabilize initially on power up so I wouldn't go as high as 10uF. If you have the EVM, I would recommend replacing the boost capacitor on that with one that is twice as large to start. If that still isn't enough, I would slowly increase from there. 

    As for the noisy output, can you provide an oscilloscope capture of the noisy waveforms? Also are you using a single ended or differential input? 

    Thank you, 

    Justin Beigel

  • 0 in reply to Justin Beigel
    Mastermind 8430 points

    Hi Justin-san,

    Thank you for your reply !

    I see, I will try to increase the capacitor.

    And about the noisy signal capture, sorry, it seems to be difficult, due to this is my customer's product.

    Thanks and Regards,