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TAS5713 inconsistent audio output generation

DJ
Prodigy 225 points
Other Parts Discussed in Thread: TAS5713

We are using the TAS5713 in a new design, and are gearing up for production. The prototype boards worked great except for a problem where on some power up cycles, we were unable to get audio out of the chip. Power cycling the board (sometimes several times) would correct the problem. There are a couple of interesting characteristics of this problem:

1. The power consumption of the board is the same whether or not the audio output successfully starts up. I am not sure how this is possible since we clearly aren't delivering any power to the (single) speaker (we are using PBTL mode), but there is a definitive jump in the current draw from the board whether or not there is any audio being driven out to the speaker.

2. We have dumped all contents of the TAS5713 internal registers and they are identical whether the audio output is successful or not.

I originally thought that the problem was related to the fact that on our first prototype board, we were not following the recommended sequencing of the reset and PDN lines to the TAS5713 chip. On our "production" board, I have a separate output line from our processor to control each line, but still no change.

Any ideas as to what might be responsible for this?

Thanks in advance!

Dave C

  • 0
    TI__Guru**** 189399 points

    Hi, Dave,

    I don't understand what you're saying in #1. Can you clarify?

    2. Good. 

    The most common problem for problems is tripping OCP due to output inductors saturating, or too much C placed in the output filter (accidentally by your board builder). Can you program the FAULT pin to report errors and monitor it?

    Can you look at the output and see what the switching waveform looks like? Any difference in switching frequency? So-called "limp" mode.

    I assume you aren't throwing any errors in the error register, 0x02, right?

    -d2

  • 0 in reply to Don Dapkus
    Prodigy 225 points

    Thanks for your response Don.

    In regards to your question on my item #1: I meant that the current draw by our board was pretty much the same whether or not we were actively driving the speaker with audio. This seemed rather strange because if we weren't pushing power thru the speaker, then how would you account for the fact that the current draw could be the same.

    The good news is that we solved this problem late last night and wanted to get the solution posted as I am sure someone else will stumble across the same problem we did. In fact, the problem wasn't related to the TAS5713 at all. It seemed to make sense that it was a hardware problem because the firmware is usually the one thing that you can count on to run consistently in these sorts of applications. We are using the NXP LPC1758 ARM chip to drive the TI PA and as it turns out, it has an errata on the configuration of the MCLK divider in the I2S interface. If the source clock (PCLK) into this divider is > 74MHz, then the errata indicates that the divider won't run. In our case it did run (which is why I wasn't looking for problems in the ARM chip), only the duty cycle was a far cry from 50%. More signficantly, this duty cycle was inverted roughly 50% of the time at initialization of the I2S driver. This was the difference between the audio working or not working on our board.

     

    Regards,

    Dave

  • 0 in reply to DJ
    TI__Guru**** 189399 points

    Dave,

    Glad to hear you got it working. You sound like a s/w guy. Me, it's always a s/w problem! ha!

    -d2