• State Resolved
  • Locked Locked
  • Replies 4 replies
  • Answers 1 answer
  • Subscribers 29 subscribers
  • Views 366 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.

Original question:

TPA3255: Transformer + LC architecture

TPA3255: D class power amp used to drive piezoelectric acoustic transducer

Sean McPeak
Intellectual 430 points
Part Number: TPA3255

Hello, I am currently working on a development project that is attempting to use the TPA3255 class D power amp IC to drive a piezoelectric acoustic transducer for an underwater application. I have purchased an eval board for the TPA3255 and have read through a post on the TI forums discussing the placement of the LC filtering in relation to the transformer driving the piezoelectric transducer. I have also been reading through the "slaa701a.pdf" LC filter design application note. I have the datasheet showing the admittance curves and transmit voltage response for the piezoelectric transducer that this project is planning on using. For my application I think I will want to use the 2-inductor, Pre-Filter Parallel Bridge-Tied Load (PBTL) mode that the TPA3255 provides. I was just curious if there were any other helpful resources that anyone might know of for this type of project. 

thank you

-Sean

  • 0
    TI__Mastermind 19080 points

    Hi Sean,

    Understood. Underwater piezoelectric applications usually use very low frequency. Please just take care of the input AC coupling capacitor design.

    Another side note is, piezoelectric transducers is actually a capacitive component. Be careful on the overcurrent situation when there is large dynamic input.

    Any question, please let us know. Thanks!

    Regards,

    Sam

  • 0 in reply to Sam(MPAA) Zhang
    Intellectual 430 points

    Hi Sam, 

    Thank you for your comments. By "input AC coupling cap design" are you referring to the DC blocking caps that I see mentioned in the data sheet for the input A, B, C and D pins?

    I am trying to better understand how the TPA3255's analog input voltage gain of 21dB is determined. I think a gain of 21dB would equate to a voltage gain factor of 11.22. I read in the datasheet that the Vin max voltage swing is 7Vp-p, yet the data sheet also mention that the inputs can swing +/-3.9V peak. If the max high power rail is 51V, is the voltage gain calculated using RMS input, peak to peak or amplitude? Perhaps the analog input gain is independent of the selected output voltage rain? Perhaps this gain is determined in the analog loop filter section? 

    For my design I believe I will need to place the LC filter before the transformer which will then step up the voltage out of the TPA3255 to the proper level necessary to produce the desired sound pressure level from the piezo acoustic transducer. My application will only involve frequency swept sine waves of a fixed amplitude. So given the fixed gain of the TPA3255 I believe I will need to determine the correct input signal amplitude and transformer turns ratio (after the LC filter) to drive the piezo transducer to the desired sound pressure level. The piezo transducer has a "transmit voltage response" curve which shows the sound pressure level out related to drive voltage as a function of frequency. So I think I need to better understand the relationship between Vin and Vout of the TP3255. 

    Thank you for your help and time.

    -Sean

  • +1 in reply to Sean McPeak
    TI__Mastermind 19080 points

    Hi Sean,

    1. Yes, I was referring to the DC blocking caps on the input pins.

    2. The voltage gain is 21.5dB, or 11.88. This means an input signal of +/-3.9V Vpeak will be amplitude to 46.3V Vpeak.

    Thanks!

    Regards,

    Sam

  • 0 in reply to Sam(MPAA) Zhang
    Intellectual 430 points

    Hi Sam, 

    Thank you for answering my questions and clarifying those issues for me. 

    cheers,

    -Sean