Because of the holidays, TI E2E™ design support forum responses will be delayed from Dec. 25 through Jan. 2. Thank you for your patience.

  • State TI Thinks Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 1 answer
  • Subscribers 30 subscribers
  • Views 379 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

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.

TPA3255: Driving piezo transducers

Zora Barabas
Prodigy 20 points
Part Number: TPA3255

Hi,

I want to amplify a ~40 kHz sine wave using the TPA3255 for my piezoelectric transducer. The transducer's resonant frequency is 40 kHz and has a bandwidth of 2 kHz. The datasheet gives me a capacitance value of 2400 pF, with an impedance graph. On the graph, the impedance is 600 Ohms at 40 kHz and around 3k at 41 kHz. I am trying to design the LC filter for the output of the TPA3255 but I don't know what load should I be using. Would it be beneficial to create an impedance matching circuit similar to the Zobel network?

I can see that the TPA3255 is mostly used for 4/8 Ohm inductive loads but would it also be able to drive the piezoelectric transducer?

Also, if I would connect two speakers to the output in parallel, how should the impedance change? Can I get a constant load somehow?

Thanks,

Zora

  • 0
    TI__Genius 15250 points

    Hi Zora

    about the LC filter design, i think below document have some information might help you.

    https://www.ti.com/lit/ds/symlink/drv5825p.pdf?ts=1679625849207&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FDRV5825P%253FkeyMatch%253DDRV5825P%2526tisearch%253Dsearch-everything%2526usecase%253DGPN

    please refer 9.1.1.1 LC Filter Recommendation chapter.

    using tpa3255 is possible to drive piezoelectric transducer. just need to consider the capacitor property which has lower impedance at high frequency which might lead to large current. but according to your info, it seems no problem.

    connect to spk parallelly, you mean 2 piezo speaker? i am not very sure how you get constant load with speaker connect parallelly.

    thanks.

    jesse

  • 0 in reply to Jesse Ji
    Prodigy 20 points

    Hi Jesse

    I checked out the document you sent but I didn't quite get what resonance frequency means there. It is only mentioned at the LC filter part. Would that be the resonant frequency of the transducer?

    Also, would you recommend using an inductor for example at the output of the amplifier to match the capacitance of the transducer?

    Yes, I would like to connect 2 piezo speaker in parallel.

    Thanks,

    Zora

  • 0 in reply to Zora Barabas
    TI__Genius 15250 points

    Hi Zora

    when you connecting output LC filter and capacitor load, the C for LC filter change so that the resonant frequency also change.

    the impedance of the load impedance will decease to a very low value so that output unstable and OC been triggered easily.

    so we need to make sure the resonant frequency should be larger enough to prevent OC or output unstable happen.

    about the inductor, you can use the formula in the datasheet to get an appropriate value. 

    for your piezo capacitance is very small and you want to output signal < 40k, so i think < 10uH should be ok for your application.

    parallel 2 piezo speaker will enlarge the load capacitance, it will enlarge the risk of oc. so using more smaller inductor would be better.

    thanks.

    jesse