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using tas5086 at lower switching rate

geert de vries
Intellectual 580 points
Other Parts Discussed in Thread: TAS5086, TAS5631, TAS5162

Hi,

We succesfully developed several pro-audio products incorporating the TAS5086

in combination with TAS4062 or 5631 bridges. These bridges run at 384KHz at an input rate of

48K samples. We are happy with the specs and performance sofar.

However, for a very specific application, I need a PWM switching rate of approx. 190K, half

the original frequency. The tas5086 is driven directly from a 6713dsp MCASP, so reducing samplerate

is not a problem. Undoubtly, the internal PLL of the modulator has to run on this lower frequency as well.

Is this possible with the TAS5086? How should this be accomplished?

kind regards

Geert de Vries

Duran Audio BV

  • TI__Guru**** 189399 points

    Hi, Geert,

    I don't think this is possible. Let me check around a little, but off the top of my head, I'd say this is not possible.

    Is this for some kind of special transducer or something that can't handle 384 kHz switching?

    -d2

  • in reply to Don Dapkus
    Intellectual 580 points

    Hi Don,

    Thanks for your reply .

    We intend to use the TAS modulator in combination with a bridge that is composed of discrete components.

    This bridge can handle supply rails up to 200Volts which we need to drive a 21"active.subwoofer

    Because we do not need a high audio bandwith and want to reduce switching losses, the idea was to run the configuration at a lower switching rate.

    The concept works, although at this moment we still run at 384K and lower bus voltage

    regards

    Geert de Vries

    Duran Audio BV

  • in reply to geert de vries
    TI__Guru**** 189399 points

    Hi, Geert,

    By using some of the AM avoidance modes, it seems like you can get the outputs switching at 288 kHz.

    -d2

  • in reply to Don Dapkus
    Intellectual 580 points

    Hi Don,

     

    many  thanks sofar,

     

    using this we can get at least below the 300K, in combination with proper gate drivers

    it seems feasible. Some other question instead...

    we switched from TAS5162 to TAS5631 in a new design. This because we needed to

    power 4 Ohms loads. We found that when TAS 5631 aproaches the supply rails, some HF ripple

    apears on the output signal, resembling the behaviour of hysteresis controlled classD designs.

    The TAS 5162 was clean until hard clipping in this respect. In the block diagram of the TAS6531 it

    seems that the signal in the TAS5631 is resampled.. is this correct?

    Is this the explanation for the different behaviour of the chip?

  • in reply to geert de vries
    TI__Guru**** 189399 points

    Hi, Geert,

    Yes, that is the effect of the feedback causing the ripple. 

    Some customer "digitally" clip instead of clipping the actual power stage.

    -d2