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tpa3125 BTL configuration

Aviad Yeshaya
Prodigy 40 points

Hello,

I'm using the tpa3125 for a single 8ohm speaker.

according to the datasheet, the output has 1 inductor in series and one capacitor to the GND for each output.

according to the Evaluation Board schematics, there is additional ferrite bead in series and more resistors/capacitors connected in parallel to GND.

I'm aware that the Evaluation Board schematics is for single ended configuration but I want to make sure what is the best practice for my application.

Moreover, some of the values of the capacitors/resistors are different between the Eval Board scheme and the application notes in the datasheet (for the same configuration) can you explain why?

many thanks 

  • 0
    TI__Guru 57800 points

    Hi, Aviad,

    Welcome to E2E, Thanks for your interest in our products!.

    The filter selection depends mainly on the user end-system requirements as speaker impedance, BOM, frequency response, etc. In general, the output filters are configured to remove the PWM switching frequency of the outputs of the amplifier by forming a low-pass filter that will remove all the content above audible spectrum. I would recommend you to take a look to page 15 of the datasheet to find out the recommended way to configure the best output filter for your end-system.

    Best Regards,

      -Diego Meléndez López
       Audio Applications Engineer

  • 0 in reply to Diego Melendez
    Prodigy 40 points

    Hi

     

    Thank you Diego,

     

    I read the relevant sections in the datasheet but between the Datasheet's application notes  and the Evaluation Board schematicsת there are some values that I do not align.

     

    When comparing Single-Ended (SE) (8-Ω Speaker):

     

    Parameter/component

    DATASHEET

    Evaluation Board schematics

    Bleeder Resistor for Single-Ended Output Capacitor

    4.7K

    None

    Output inductor

    22uH (page 19)

    33uH

    Filter capacitor

    680nF(page 19)

    220nF

    FB3,FB4 (Eval schematics page 5)

    Do not exist

    exist

    R5,R6,C16,C17 (Eval schematics page 5)

    Do not exist

    exist

     

    So my question is what should I reference in my design since I am no Audio expert.

     

    Ultimately my configuration is Bridge-Tied-Load (BTL) Configuration (8-Ω Speaker) but since I don’t know if I can rely on the datasheet I need to verify the Single-Ended (SE) (8-Ω Speaker) first

     

    I hope that's clearer

  • 0
    Prodigy 40 points
    Hi,
     
    Any progress?
     
    Best Regards,
    Aviad Yeshaya
    Senior HW Engineer
    McKesson Cardiology, Medical Imaging Group
    International:   +972 3 6797301
    Mobile:             +972 54 4665502
    Fax:                   +972 3 647.8593
    26 HaRokmim St. (Azrieli Center 1, Building A, Floor #3)
    Holon, 5885849, Israel
     
  • 0 in reply to Aviad Yeshaya
    TI__Expert 6720 points
    Hi Aviad,

    It's completely clear of your concern. Thanks again for your patience with our products.

    First of all, I'd like to share you some points of why different output filter between TPA3125 datasheet and EVM:
    1. EVM FB3 - R5 - C16 and FB4 - R6 - C17 are two channel snubber circuit, and the main function is to change PWM slew rate for better EMI performance. So if EMI issue is not your syetem main concern, you can leave out this part.
    2. Bleeder Resistor for Single-Ended Output Capacitor of EVM is R7 and R8, and the different value means different discharge time of the output capacitor which you can take datasheet page 15 as reference for this part.
    3. The output filter L1 - C18 at EVM use 33 uH and 0.22 uF for better performance of 8 ohm load, and datasheet 22 uH and 0.68 uF is for 4 ohm load. You can also take a look of datasheet page 15 for this part.

    What's more, if you want to test 8 ohm speaker single ended first, it's better to use datasheet output filter circuit with 33 uH and 0.22uF. For your final BTL configuration, please follow the output filter parameters as datasheet Figure 30 structure and value.

    Hope you have a nice product experience.

    Best Regards,
    Matthew