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TPA3106 frequency response

Moritz Bente
Prodigy 75 points

Dear e2e Community,

I've made an Amplifier design using the TPA3106 for powered Speakers and i have a bit trouble with the Frequency Response.

My System is using a 19 V PowerSupply and i have tested also a couple of Inductors in the Output path. I've build 5 PCB's with all the same malfunction.

The Gain setting is set to: 20 db.

I've also changed the input caps to another values (from 1uF ... to 1000uF) but no difference in the response.

The Schematic and the Values are the same as  shown in the Datasheet page 14. 

The Frequency response is like a Highpassfilter with a cut of frequency in the near of 250 Hz. I've attached my measurements. 

Does anybody have an idea why my frequency response is not linear like its printed in the datasheet? 

Actually this is not usable for my requirements.

Hopefully thanks for every idea to solve my problem. The THD is also not okay but thats another Question to another time. 

Thank you very much

Moritz Bente

  • 0
    TI__Expert 7925 points

    Dear Moritz,

    How peculiar what you're seeing! I will investigate what might be causing this.

    Does the layout on your PCB follow the design of the EVM pretty closely? The PCB layers are shown in the TPA3106D2EVM User's Guide.

    Are the components you are using similar in rating to the ones in the BOM on the User's Guide?

    On your board, what connector do you use for the input of the amplifier? RCA jacks?

    What happens to your response as you change the capacitor value on the output of the amplifier? Does it change this high pass filter at all?

    Best Regards,
    Matt

  • 0 in reply to Matt Lauer
    Prodigy 75 points

    Hey Matt,

    thank you for your response! The layout is quite equal to this in the EVM. If its useful i can send you an image of the layers per mail. The Values i've used are from the user guide.

    The connector i used for the input is a RCA Jack and 4 cm cable. All is mounted on a 2mm aluminum plane.

    Is there a difference while the Amp is without load? Eventually i have to connect a 8 ohm resistor to the output and measure again?

    Which output capacitor do you mean? The C9 & C8 are actually 1uF?

    Which value do you prefer?

    Best Regards,

    Moritz

  • 0 in reply to Moritz Bente
    TI__Expert 7925 points

    Hi, Moritz. I sent you a friend request on E2E. As my friend, you can send me the image of your PCB layers through a private message on E2E. I'd like to see them.

    Can you see what your measurement looks like with an 8 Ω load attached? Are you saying you made this measurement without a load attached?

    I meant both output capacitors C8 and C9. They should be 1 µF in value if you followed the EVM, but I would like you to change them to, say, 10 µF to see what effect it has on your measurements. It would be interesting if it changed the lower frequency behavior.

    Best Regards,
    Matt