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PWM source for digital-input power amplifiers?

Carlos Moreno1
Intellectual 550 points
Other Parts Discussed in Thread: TAS5624, TPA3251, TAS5624ADDVEVM

Hi,

I'm looking at the TAS5624 and TAS5261 amplifiers --- I was hoping that they would accept a PCM stream through an I²S standard connection, but as I understand from the datasheet, this is not the case.

Is this PWM input that these amplifiers expect some standard format that I could expect DSP chips to produce?   For the project I have in mind right now (hobby/DIY level), I'm planning to get audio from a PC through USB (using the PCM2707), output PCM through I²S to an ADAU1701 (from the Analog Devices SigmaDSP series) for processing.  Should I expect that this DSProcessor will be able to output PWM data that the TI amplifiers accept?

If not, I guess what I would be looking for is a PCM-to-PWM converter --- I could not find any through the products section on TI's web site.

Any tips/pointers will be appreciated.

Thanks,
Carlos
--

  • 0
    TI__Guru 65490 points
    Carlos,

    What power level do you need? It looks like you're designing for ~300W Mono.

    You are correct that the TAS5261/TAS5624 devices accept only PWM input and not PCM input. That being said, you have a few options.

    1. Use one of our PCM Audio DACs (www.ti.com/.../audio-dac-product.page) which would accept PCM data from your DSP and output analog audio that could be sent into one of our Analog input amplifiers such as our TPA3251. I am suggesting the TPA3251 as it looks to be of similar power level.

    2. You could also use one of our PWM modulators such as the TAS55xx to convert your DSP PCM to PWM. This is slight overkill since it has 8 channels but it's doable. The TAS5624ADDVEVM contains a TAS55xx device and the TAS5624 for this purpose.

    Regards,

    -Adam
  • 0 in reply to Adam Sidelsky
    Intellectual 550 points
    Thanks Adam.

    Option 1, I had already considered, and I may end up taking that route for now --- actually, no need for DAC if I use the ADAU1701, which has 4 on-chip DACs of reasonably good quality (in any case, well above the quality of the class-D amplifier, I estimate).

    As for option 2 --- since you're a TI employee (or in any case, the TI people reading this), please pass along my feedback/suggestions on this issue:

    I believe it does not make a lot of sense to design these amplifiers with this limitation. I mean, at the very least, if you had a simple-and-inexpensive option to modulate a PCM stream into the PWM to feed the amplifier, ok. But if the only option to make them work is an "overkill" solution, where's the usefulness in these digital-input amplifiers? In my opinion, what makes most sense for a "digital input" class-D amplifier is to accept PCM data through an I²S connection.

    With that said --- in my particular application, the TSA5558 may not be overkill after all --- the "processing" that I want the DSP for is nothing other than a digital crossover; so, I will end up with multiple audio streams anyway and thus the 5558 may be useful. (still, this does not negate my point in the previous paragraph --- my view is that I should not need it at all).

    Thanks,
    Carlos
    --
  • 0 in reply to Carlos Moreno1
    TI__Guru 65490 points

    Carlos,

    Thank you for the feedback. We do have some devices that accept PCM input but they are for lower power levels than you need. I think they are max 30W or 50W.

    Please let me know if we can help further. 

    Regards,

    -Adam