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Original question:

TAS5754M: TAS575x SPKIN as a general input

TAS5754M: Analogue mute

philippe_44
Prodigy 250 points
Part Number: TAS5754M

Hi - I'd like to mute only the amplifier part of the TAS575X, and I thought the SPK_MUTE input would do that, but it also mutes the digital part, which means there is no more analogue audio at the DAC output. The use case is to use DAC_OUT (which is connected to a headset amp) but mute the speakers (which are connected to the TAS575x amplified outputs) when, for example, a jack headset is inserted.

Thanks

Philippe

PS: I've seen here https://e2e.ti.com/support/audio/f/6/t/526429?Problem-with-TAS5756-as-I2S-master that some did that by mistake, so it seems to be doable to only power off the analogue stage.

  • 0
    TI__Expert 6720 points

    Hi Philippe,

    TAS575X devices do not have one alone analog amp MUTE feature.

    As for Master Clock triggering DAC output without Analog output, did you confirm the DAC output is correct? 

    What's more, the only possible option coming to my mind is to configure TAS575X into PBTL mode, which means BTL Speaker connection does not see the audio output. However, it needs hardware switching to PBTL mode. 

    Regards,
    Matthew

  • 0 in reply to Matthew Miao
    Prodigy 250 points

    Thanks Matthew - ah ... this is really (really) unfortunate and ruins one of my key use cases. I don't know for sure that in the other thread the DAC output was correct, but the OP was pretty assertive about that: with a scope he sees the output of DAC active and he connected an amplifier to it and got the correct audio, so seems to be a very solid proof. Is there really no test mode or no way to trick the TAS575x (which seems to be the case in the other post)? It seems really strange to have the DAC output available and not being able to isolate it. The TAS has an analogue mute (per documentation, it can be triggered after digital mute), so, it's very strange that there is no way to trigger that mute manually. Any undocumented option (please)?

    Wrt to your comment on PBTL, I'm not sure I'm following. This require a different wiring, which does not fit the use case of user inserting a jack and muting the amp while still having the audio on his headset 

    Philippe

  • 0 in reply to philippe_44
    Prodigy 250 points

    Something I've been able to do

    - Set P1, R6 to 0 (analogue mute follows digital)

    - Set P0, R3 to 0x01 or 0x10 will mute one digital channel and the *whole* analogue stage, so on the DAC the other channel remains active alhough both analogue (the whole stage) are muted... damned there has to be a solution :-)

  • 0 in reply to philippe_44
    Prodigy 250 points

    Hi again - I also TAS5780 which seems pin-to-pin compatible and have the analogue control function ... BUT ... it has a reset/ pin and I don't see a pull-up inside, so does it have to be pulled up and can it be direcly tied to 3.3V? 

  • 0 in reply to philippe_44
    TI__Expert 6720 points

    Hi Philippe,

    It's one good workaround. I tested with EVM board, and it does work as below:

    • Initialize TAS5754M, both DAC/Amp output are correct.
    • Write down script:
      • w 98 00 01
      • w 98 06 00
      • w 98 00 00
      • w 98 03 01
    • No audio output with both two channels ClassD. But there is still audio output with ChannelB DAC output

    Regards,

    Matthew

  • 0 in reply to Matthew Miao
    Prodigy 250 points

    Thanks Matthew for confirming my attempt, but per my previous post, that unfortunately only enables channel B DAC (or A if 0x10 is written in R3) where I need A and B. How can I do?

  • 0 in reply to Matthew Miao
    Prodigy 250 points

    I'm now trying the TAS5780. Audio works fine, but page 253 contains registers that should allow me to mute analogue (register 37 and al) does not seem to be accessible / work. When reading the whole page, everything always returns 0

  • 0 in reply to philippe_44
    Prodigy 250 points

    After many trials & error, I've finally used R46 on P0 that allow "backend" to be powered down on TAS5780. It's very important to first put the chip in standby mode because disabling backend causes something that leads to current consumption peak of 1.5+A before shutting down. 

    - P0, R2 ==> 0x10

    - wait 50ms (maybe less) for the chip to actually be in standby

    - P0, R46 ==> 0

    -P0, R2 ==> 0

    With that, DAC_OUT is still active but there is not audio on SPK_OUT

    To switch it back on, just do the same sequence but write 1 in R46

    Hope this will help somebody else

    I think the TAS documentations deserves a bit more attention on registers and their usage, in which conditions can they be accessed or not, does standby need to be activated or not, why some pages are unacessible... It's really unclear.

    It's really unfortunate that the TAS5754/6 does not expose the analogue control as it obviously does exist and it's feasible to switch it off/on by software, just it's not documented. I wish there is an accessible kit to write some DSP code and download it in RAM