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TPA3251D2-EVM

Thomas Deuble
Intellectual 550 points

Just a simple questing: 

The film capacitors on the TPA3251D2 evaluation board are rated 250V.

Can I also use capacitors with a lower voltage rating to save space since the power supply voltage in my application will be 34 volts only.

Thank you very much and kind regards,

Thomas

  • 0
    TI__Mastermind 34665 points

    Hi Thomas,

    The cap on the the TPA3251D2 are rated for 50V. The next lower voltage rating is 35V, but it is too close to your working supply voltage, which can result in degraded performance from the cap operated close to the rated voltage.

    The lowest voltage rating we would recommended 50V.

  • 0 in reply to Damian Lewis
    Intellectual 550 points
    Hi Damian,
    thank you very much for your answer.
    On the evaluation board of the TPA3251D2 the caps C24, C35, C43 and C59 are rated 250V.
    Is there any reason for that. Should I use also caps rated 250V in my design?
    Kind regards,
    Thomas
  • 0 in reply to Thomas Deuble
    TI__Mastermind 34665 points

    Hi Thomas,

    Yes you're right. the class D output filter caps are high voltage film capacitors the can tolerate high pulses (dv/dt) and high temp. We chose those based on the linear performance for high power applications. The capacitance remains constant with voltage for TPA3251D2 voltage range. It's partly due to the fact the TPA3251D2 voltage range is way below the DC and AC voltage rating of the EPCOS caps.

    Sorry for the confusion. I hope info helps. If you can I would recommend using the same caps or similar caps. You're welcome to try different caps like WIMA base on your specific application need, but I don't recommend using any caps with voltage rating <50V.

  • 0 in reply to Damian Lewis
    TI__Guru**** 189399 points
    Hi, Thomas,

    Let me expand on Damian's response. Most capacitors have an applied voltage derating curve - the closer you operate to the cap's voltage rating, the less effective capacitance you realize.

    So, the problem is, as the voltage changes on the output, the capacitance value changes, and this affects the attenuation of the LC filter and results in non-linear distortion in the output.

    As Damian mentioned, using a higher rated cap solves this, as does using something like the EPCOS cap which has a smaller dependency on applied voltage.

    -d2
  • 0 in reply to Don Dapkus
    Intellectual 550 points

    Thank you very much, Don.

    This is a very satisfying answer :-)

    T

  • 0 in reply to Thomas Deuble
    TI__Guru**** 189399 points
    You're welcome, Thomas!!!

    Let us know if you have any further questions.

    -d2