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TAS5613 PVDD capacitance limit

Pierre Watts
Prodigy 155 points
Other Parts Discussed in Thread: TAS5613

Hi,

I'm designing 3x TAS5613 in a 6-channel application, powered with a 500W DC-DC half-brick supply (Synqor IQ24 series). Trouble is, the supply has a maximum stable load capacitance limit of 1000uF, and with the design guideline recommending 1000uF per half-bridge output I need 12,000uF total for 6 channels.

Question is therefore what will happen if the PVDD capacitance gets dramatically reduced from 1000uF to 68uF? With linear or offboard positioned supplies, THD will probably spike at higher power, but the supply has line and load regulation of +-0.25% and will be mounted within 70mm from the chips on the same PCB, with its sense line connected straight to the load split.

Max power requirements are 90W/ch in 6ohms.

Regards,

Pierre

  • 0
    TI__Mastermind 18510 points

    Pierre, of course reducing the bulk capacitance (the 1000uF per channel) can result in higher power supply ripple and distortion at moderate to full output power.  But if you are confident in your power supply, and you can sense very close to the 3 TAS5613, you may be able to make this work with performance that is acceptable to you.  

    I would recommend several things to try to make this work best.

    - Use 4 x 150uF at each TAS5613, totaling 900uF, acceptable to the power supply.

    - Connect the power supply sense line at the load split as you suggested.

    - Use very heavy copper traces between the load split and the 150uF bulk caps for each TAS5613, so power supply regulation will help to control ripple there.

    - Follow the PCB layout in the EVM very closely, particularly the grounding and location of all decoupling caps.  I encourage you essentially to copy the EVM layout.

    You will need to determine what size power supply traces are required for the level of performance you want.

    I understand why you need to do this, and I wish you success.  Please let me know how this works.

    Regards,

    Steve.

  • 0 in reply to SteveCrump
    Prodigy 155 points

    Hi Steve,

    Thanks for the detailed reply. Would you rather recommend using 6x 150uF instead of 12x 82uF?

    I know there are a huge amount of variables, but if the target 70W/ch @ 6ohm is likely to exceed 1% THD I'll have to find a different solution..

    Regards,

    Pierre

     

  • 0 in reply to Pierre Watts
    TI__Mastermind 18510 points

    Pierre, your math is better.  I think you want to use 4 x 82uF per TAS5613, replacing the 4 x 1000uF normally used.  You will also want to use power supply voltage of 36V.

    I think you can try this and see if it achieves your target.  I believe there is a good chance it will.

    Regards,

    Steve.

  • 0 in reply to SteveCrump
    Prodigy 155 points

    Hi Steve,

    Thanks I'll give it a try  - however I can't use 4x 150uF per chip as there are 3x chips for 6 channels. That is why the 4x 1000uF has to come down to 4x 82uF per TAS5613, since 12x82 = 984uF.

    Regards,

    Pierre

  • 0 in reply to Pierre Watts
    TI__Mastermind 18510 points

    Pierre, your math is correct.

    Regards,

    Steve.