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Interfacing a piezo speaker to the TLV320AIC3120

Dave 1024
Intellectual 470 points
Other Parts Discussed in Thread: TLV320AIC3120, TPA2100P1

I am a new-B when it comes to audio, so this might be a silly question. I am putting together a very thin audio recording/playback device that must be no taller than 1/8", and this project requires a very thin speaker. I ordered a APS2718S-T-R piezo speaker from PUI Audio Inc. for no particular reason other than DigiKey had them in stock, it looks cool, and it's REALLY thin. I want to glue the piezo speaker to a TLV320AIC3120 because I'm pretty sure I will need the filtering capabilities, and I want to justify my purchase of the EVM board that just showed up in the mail. The TLV part has a class D 8-ohm speaker output. I understand I cannot connect the piezo speaker to the TLV part because the impedance and voltage levels are all wrong, so I was going to use the line output from the TLV part and feed that to a TPA2100 class D piezo driver chip and not use the speaker driver output from the TLV device. I'm wondering if it would be any better to use a transformer instead and drive the piezo speaker using the speaker driver on the TLV part through the transformer and save battery power by dumping the piezo driver chip. Is that dumb? If I have a step-up transformer made with a primary impedance of 8-ohms and a secondary impedance of 300 (the impedance of the piezo) with about a 5:1 turns ratio, can that eliminate the TPA2100 driver chip? Any better suggestions?

 

Thanks!

Dave

  • 0
    TI__Genius 16645 points

    Hello Dave:

    From your forum post, it appears that you are thinking about the right things in your design.

    I would not recommend the transformer approach because:

    1. They are large and may impact the height/size of your design
    2. A transformer with sufficient quality not to produce audible artifacts will be more costly that implementing the TPA2100P1
    3. You may have "pop" issues when you enable the amplifier because you are stepping up the the start-up and shutdown artifact of the AIC3120 with the transformer
    4. The piezo is a capacitor and its impedance drops with frequency.  The transformer will be less stable than an amplifier directly it; therefore, you may have distortion issues

    From our experience, I believe that the TPA2100P1 is the best approach for your application.

    Regards,

    Fred

     

     

     

     

  • 0 in reply to Fred Shipley
    Intellectual 470 points

    Thank you for those comments, they make sense. I will go with the TPA 2100P1 device.

    Regards,

    Dave