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TAS5538 Internal Behavior During Clock Error

Sadanori Kato
Guru 36490 points
Other Parts Discussed in Thread: TAS5538

Hi,

TAS5538 can automatically detect the clock error as below.
Could you please tell me the internal behavior during the clock error when halting SCLK and LRCLK ?
An audible noise is heard from the speakers if touching the external components for the pll loop filter when halting only LRCLK.
So, I have some questions as below.

Q1. LRCLK Error
Are the pwm outputs generated by the internal osc clock if halting only LRCLK ?
Or are they generated by MCLK ?
However, MCLK and SCLK are applied to TAS5538.
It seems that they are generated by the internal osc clock.

Q2. SCLK Error
Are the pwm outputs generated by the internal osc clock if halting only SCLK ?
Or are they generated by MCLK ?
MCLK and LRCLK are applied to TAS5538.
It seems that they are generated by MCLK.

Best regards,
Kato

  • 0
    TI__Guru 57800 points

    Hi, Kato-san,

    Sorry for the delay, my colleague is looking at  this and will get back to you soon with his comments.

    Best Regards,

      -Diego Meléndez López
       Audio Applications Engineer

  • 0
    TI__Guru 61360 points

    Sadanori-San,

    Thanks for your post.

    The internal OSC clock will keep the device running in a limited mode if any of the clocks stop. This running mode is necessary for the device to monitor the other clocks while the device waits for normal clocking to resume. 

    This being said, the PWMs are still switching while one or more of those clocks are stopped. The sound you are hearing is probably the Noise shaping as this still operates as long as the PWMs are still switching. 

    Regards,

    -Adam Sidelsky

  • 0 in reply to Adam Sidelsky
    Guru 36490 points

    Hi Adam-san,

    Thank you for your response.

    I have some questions.
    So, does TAS5538 work by using only internal osc clock even if supplying MCLK and LRCLK when halting only SCLK ?
    In other words, MCLK and LRCLK aren't used.
    In addition, does TAS5538 work by using only internal osc clock even if supplying MCLK and SCLK when halting only LRCLK ?
    In other words, MCLK and SCLK aren't used.

    Best regards,
    Kato

  • 0 in reply to Sadanori Kato
    TI__Guru 61360 points

    Sadanori-San,

    I don't follow your questions. What do you mean by "does TAS5538 work"? Are you asking if the device is in normal operation? Or are you asking if the PWMs are switching?

    You mention that MCLK and LRCLK are supplied and then you say that MCLK and LRCLK are not used, this is confusing.

    Regards,

    -Adam

  • 0 in reply to Adam Sidelsky
    Guru 36490 points

    Hi Adam-san,

    Sorry for confusing you.

    I would like to confirm whether TAS5538 operates by only the internal osc clock during the clock error or not.
    Of course, I believe that the pwm switching works at 50% duty.
    For instance, the clock error occurs if halting LRCLK, however MCLK and BCLK continue to be supplied to TAS5538.
    In this case, does TAS5538 operate by only the internal osc clock regardless of whether MCLK and BCLK are supplied or not ?
    Or does TAS5538 operate by using not only the internal osc clock but also MCLK and BCLK ?

    By the way, could you please give me your advice about the following post ?

    https://e2e.ti.com/support/amplifiers/audio_amplifiers/f/6/t/559585

    Best regards,
    Kato

  • 0 in reply to Sadanori Kato
    TI__Guru 61360 points

    Sadanori-San,

    The device will only play Audio and work correctly if all external clocks are supplied and configured correctly.

    If any of the clocks are missing, the device will not play audio, the internal oscillator will be used by the device to keep the part alive so it can monitor the inputs and wait for normal clocking to resume. The oscillator also enables the device to communicate over I2c so that commands can still be written even though the correct clocks are not present. 

    I will respond to the other post. 

    Regards,

    -Adam

  • 0 in reply to Adam Sidelsky
    Guru 36490 points

    Hi Adam-san,

    Thank you for explaining so politely.

    Is my understanding correct that TAS5538 operates by only the internal osc clock without using MCLK, SCLK and LRCLK although TAS5538 only monitors the MCLK, SCLK and LRCLK during the clock error as a confirmation just in case ?

    Best regards,
    Kato

  • 0 in reply to Sadanori Kato
    TI__Guru 61360 points

    Yes, That's correct.

  • 0 in reply to Adam Sidelsky
    Guru 36490 points

    Hi Adam-san,

    Thank you for your reply.
    I understood.

    Best regards,
    Kato

  • 0 in reply to Sadanori Kato
    Guru 36490 points

    Hi Adam-san,

    I have an additional question.
    Does TAS5538 generate the audible noise if LRCLK is held to "high" when supplying MCLK and SCLK and halting only LRCLK ?
    It seems that the audible noise occurs if LRCLK is held to "high", however doesn't occur if LRCLK is held to "low".
    That auditorily isn't the white noise due to the noise shaper.
    Could you please tell me about that difference in the operation by the logic of LRCLK and verify TAS5538 about it ?

    Best regards,
    Kato

  • 0 in reply to Sadanori Kato
    TI__Guru 61360 points

    Kato-San,

    If LRCLK is not running, there will be no audio output. I think what you are seeing is some kind of coupling from something else on the board. Can you show us a scope image of the noise or give us other details?

    Regards,

    -Adam

  • 0 in reply to Adam Sidelsky
    Guru 36490 points

    Hi Adam-san,

    Thank you for your support.

    As you said, TAS5538 is muted at 50% duty cycle during LRCLK is halting.
    Therefore, we cannot investigate the root cause even if getting a scope image by using an oscilloscope.
    The audible noise sounds like a little wind noise and the volume cannot be adjusted since TAS5538 is muting.
    So, could you please verify whether this issue is replicated or not ?
    We are asking our customer for more information.

    Best regards,
    Kato

  • 0 in reply to Sadanori Kato
    Guru 36490 points

    Hi Adam-san,

    Could you please check my email since I have already sent more information to you ?

    Best regards,
    Kato