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TAS5805M: over current and AGAIN calculation

Piocky
Intellectual 310 points

Part Number: TAS5805M

Hi there,

We are making some tests with the TAS5805MEVM board and a new speaker we want to add to our next product (in PBTL configuration), but we're having some overcurrent issues on certain songs. Those are the specs of the speaker we are testing (16ohms/60W rms). The power supply used in test is 24V/3A, but we will use 20V (USB-C PD) in the future.

We read the registers when the fault happens, and we see only register 0x70 changing (value 0x01, so right channel over current fault).

I saw this thread about the calculations of AGAIN and AGL, but I don't get where the formulas are coming from. Could someone give my some hints on those? We would like to validate that the TAS580M could be use to drive this new speaker.

I also saw this thread discussing the modulation mode and switching frequency recommended for a particular case, but can't really find clear suggestion for our needs.

Any help on this would be very appreciated.

Yoann

  • 0
    TI__Genius 16370 points

    Hello Yoann,

    Section 3.1  in the TAS58XX Tuning guide https://www.ti.com/lit/an/slaa894/slaa894.pdf?ts=1675288258952  should give you guidance on configuring AGAIN.

    best regards,

    Luis

  • 0 in reply to Luis Fernandes de Pina
    Intellectual 310 points

    Hi Luis,

    Thanks for your quick answer, I did find this section while waiting. If I do the maths correctly, with PDD = 24V, RL = 16ohms and ZDC = 0.039ohms, it gives me -2dB for AGAIN. (I was wondering if the formula is the same for both BTL and PBTL configurations?)

    For AGL, I'm not sure with the formula: Vpeak = SQRT(Prms * RL) * SQRT(2), if yes it gives me 43.81V, so I guess AGL = 0dB. Is that correct?

    Regarding the modulation mode, does it have an influence on the over current problem? I saw this document discussing them, but it seems to me that it's more related to idle current than comsuption current, but maybe I'm wrong.

  • 0 in reply to Piocky
    TI__Mastermind 20541 points

    Hi Piocky

    your calculation is correct.

    your speaker can suffer very high power, so AGL doesn't need limitaion.

    you still have oc problem with your config?

    thanks.

    jesse

  • 0 in reply to Jesse Ji
    Intellectual 310 points

    Hi Jesse,

    Thanks for the confirmation.

    If we set AGAIN to -2dB, we don't see overcurrent fault anymore, but then the volume is quite low. We can increase digital gain up to 4dB before seeing overcurrent again. But this is with the first amplifier of the EVM (the one with ferrite beads). If we use the second amplifier, we can go up to 10dB, and this time we start reaching the limit of the speaker. So very good news as it means we can use this amplifier with appropriate inductors to drive our speaker :)