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TAS5631 PWM input - can we skip using TAS5518 as modulator but use a TI DSP instead?

Jonathan Yeo
Prodigy 20 points
Other Parts Discussed in Thread: TAS5631, TAS5518, TPA3100D2

Hi TI audio folks

We have design a TAS5631 into our audio application, hardware manufactured and done. We had previous advice from the local UK TI support previously that we can skip having a TAS5518 as a PWM input to the TAS5631, part of the reason was PCB space constraint, but I think we have hit a big rock on this design as the PWM output from the TAS5518 does not look like a normal PWM but more of a Pulse Density Modulation (PDM), is this correct as the datasheet is quite vague on this. The issue we are facing now is how to generate an equivalent PWM signal of TAS5518 to be input to TAS5631.

On the TAS5631 EVM, the output of the TAS5518 looks like a PDM (Pulse Density Modulation) type of PWM? May you advise me if TAS5631 can simply take any PWM signal (as the TAS5631 video says it's a pin to pin compatible for PWM) or it must specifically take the format, PDM?, from the output PWM of TAS5518.

Our aim is to achieve generating the PWM input to the TAS5631 by a TI DSP timer and would need some advise on the format of the PWM urgently. Generating a PWM triangle signal and do a comparator with the audio signal within the TI DSP is easy, but the input of the TAS5631 doesn't seems to take a normal comparator PWM output?

I hope my questions are not confusing, thanks 

 

 

  • 0
    TI__Guru**** 189399 points

    Hi, Jon,

    I am not super familiar with the TAS5518 (it's from another group inside TI), but I am 99.3% sure that it uses standard run of the mill PWM. What makes you think it's PDM?

    The one thing that may be confusing is the fact that we have two PWM lines from the 5518 to 5631. This allows us to operate in BD modulation which may be what is confusing you. BD modulation is described in a lot of our data sheets, like TPA3100D2, for example.

    The input format of the TAS5631 is pretty much unconstrained.

    -d2 

  • 0 in reply to Don Dapkus
    Prodigy 20 points

    Hi Don

    It's PWM afterall. We measured the PWM on 2 different pins based on a older EVM datasheet. Thus the impression of PDM. The PWM implemented on the TI DSP is working fine at the moment but we have hit a little issue with input to the TAS5361. The READY pin on TAS5361DKD seems to be always near zero and we can't get the SD and OTW to get out from its start up mode. By the way, it's a customed board with no TAS5518.

    As per datasheet, TAS5361DKD don't need a reset but we have included a 1 to 10ms reset time to assert the RESET pin low before setting it high again. But we can't seems to get SD and OTW to be asserted to zero, therefore READY is always zero. We have measured RESET pins, all input voltages and the levels are correct.

    Was wondering if you might any light to shed on this, Don? Greatly appreciated. I know it's difficult to diagnose from your perspective, but any suggestion greatly appreciated.

  • 0 in reply to Jonathan Yeo
    TI__Guru**** 189399 points

    Hi, Jon,

    Sorry, I was on the road the past couple weeks.

    Did you get this figured out?

    -d2