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TAS5715 EVM schematic

Sven Krauss
Prodigy 60 points
Other Parts Discussed in Thread: TAS5715, TAS5715EVM

Hello!

I have made a board with the TAS5715. The board is based on the TAS5715EVM. My board has a much higher current consumtion without any load. I figured out, that a part of the output filter is the reason for the current consumption.

The TAS5715EVM schematic shows a RC combination 3.3Ohm and 10nF (R11/C28) directly connected at the PWM outputs. The TAS5713EVM is very similar but the RC combination is connected behind the inductor. I think the TAS5713EVM version is correct whereas the position the RC combination at the EVM5715EVM isn't.

  • 0
    TI__Mastermind 22965 points

    Hi Sven,

    The RC-network can be placed at either location (pre-filter or post-filter). Depending on the location, the RC-network serves a different purpose.

    The pre-filter RC snubber is used to minimize the PWM spike voltage caused by board parasitics. The pre-filter netwrok will result in a higher current dissipation compared to the post-filter netwrok, since it is being driven directly by the PWM's. (Current draw is ~ C*V*V*F where C is snubber capacitance, V is supply voltage, F is PWM switching frequency)

    You may also find the following E2E post relevant for this discussion. http://e2e.ti.com/support/amplifiers/audio_amplifiers/f/6/t/214461.aspx

    -Ravi

  • 0 in reply to Ravi Singh
    Prodigy 60 points

    Hi Ravi,

    the dimensioning of the pre-filter RC snubber seems to be very hard. 10nF and 3.3Ohm. (Note that the same values are used in the pre-filter snubber (TAS5715EVM) and in the post-filter snubber (TAS5713EVM)).

    The power loss of the pre-filter snubber with 10nF and 3.3Ohm is about 0.5W at 12V at one of the four RC-networks.  An other pre-filter snubber (TAS5711EVM) uses 330pF and 18 Ohm. This seems to be more realistic. 

  • 0 in reply to Sven Krauss
    TI__Mastermind 22965 points

    Hi Sven,

    You are right, having a 10nF cap in the pre-filter RC snubber will draw significant power, and a 330pF to 680pF is an optimal range.

    Sorry about the EVM schematic showing the 10nF, we will get this fixed for future bord builds. Please go ahead and update your board schematic to a 18R+330pF value. 

    -Ravi