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Questions about TAS5707EVM

Hongliang Tian
Prodigy 40 points
Other Parts Discussed in Thread: TAS5707EVM, TAS5711

Hello,

  I have one TAS5707EVM on hand, and I'm a little confused about the RC snubber (R10, C35) on this board. Usually we will say using snubber as close as possible to the output pin to filter out the high frequency content, but how about this one? I have compared it with TAS5711, TPA3110 EVM manual, It seems the position of the RC snubber has some differences.

  Could you show me why? Thanks. 

  • 0
    TI__Mastermind 22965 points

    Hi Hongliang,

    The TAS5707EVM does not have a pre-filter RC snubber network, but rather a post-filter RC network (i.e. R10+C35 you were referring to). The pre-filter snubber helps to damp out PWM spikes and ringing, and you are absolutely right in that it should be placed close to the output pins. The post-filter RC network helps with EMI performance, especially in modulation modes like BD, which have higher common-mode content.

    -Ravi

  • 0 in reply to Ravi Singh
    Prodigy 40 points

    Hello, Ravi

       Thanks for your reply. When mentioned about EMI, could you show me the main contribution of it? The spike and ringing, the 10th or above order frequency component of the PWM or others? I don't have a spectrum analyzer and can't do the analysis like that.

      What's the main purpose of eliminating spike and ringing, EMI? Do we choose pre or post-snubber because of the main contributor of EMI? 

      I'm sorry for so many questions.

    Best Regards!

      -Nic

  • 0 in reply to Hongliang Tian
    TI__Mastermind 22965 points

    Hi Nic,

    The board parasitics (inductance etc.) influence the PWM spikes and ringing levels at the output.From a device reliability perspective, it is important to keep the spike's under check. If you look at the abs-max table in the datasheet (page-7), there is a spec for OUT to PGND max level. The snubber also helps to dissipate the energy in the PWM spikes, that may have otherwise contributed to the EMC radiation. In general, just using a pre-filter RC snubber should be sufficient. 

    Here are some snubber articles you may find helpful..

    http://www.ti.com/lit/an/slva255/slva255.pdf

    http://www.newark.com/pdfs/techarticles/cornell/design.pdf

    - Ravi

    -Ravi

  • 0 in reply to Ravi Singh
    Prodigy 40 points

    Hi Ravi

      Thanks for your detailed explanation and useful articles!