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TAS5424 Mute time

David Edmondson
Prodigy 60 points

I am using a TAS5424 and I want to perform a clickless mute (~1ms) during a 10ms power dropout. It is important to mute the audio to reduce power so the PSU can holdup during a 10ms power dropout.

However the mute takes 20ms after asserting the nMUTE pin low which is far too long. Investigation has shown that if the nMUTE pin is clamped externally to a maximum of 5.8V the mute time reduces to <1ms.  This gives the desired operation.

Could you please explain this behaviour and suggest the recommended way for ensuring the nMUTE pin operates quickly?

nMUTE pin has a 220n capacitor.

Supply is 15V.

  • 0
    TI__Mastermind 45085 points

    Hi David,

    This is the correct methodology to mute quickly.  Use a transistor that pulls down on the nMute pin.  There is no need to pull up the pin as it is done internally.  The nMute pin controls the Mute of the device.  Typically, we control it internally for turn on and turn off through I2C commands.  Be careful pulling it down.  If it is pulled down externally, the internal state machine could be stuck at this point.  Do not run I2C commands when the nMute pin is pulled down.

  • 0 in reply to Gregg Scott
    Genius 3295 points
    Hi Gregg,

    That is an interesting little tidbit you threw out there; no I2C when pulling nMute low. Is this particular to this device, or in general would you say this is the case?

    Thanks,

    Mike T.
  • 0 in reply to Mike Tripoli
    TI__Mastermind 45085 points

    Hi Mike,

    The I2C is still functional.  One can read and write to the registers.  The problem is when the device has an external mute, forcing the nMute pin low, it cannot move from this state to Play or Hi-Z through I2C.  In this case, the device thinks it is in Play mode and the external mute forces the outputs to mute. If the nMute pin is released, it returns to play mode.  The internal state machine does not know the device was forced into mute.  I hope this clarifies my earlier statement.

  • 0 in reply to Gregg Scott
    Genius 3295 points
    Understood. Thanks very much, Gregg.

    Mike T.
  • 0 in reply to Gregg Scott
    Prodigy 60 points
    Hi Gregg,
    I am using a transistor to mute on the nMUTE pin. The problem is it takes 20ms time for the amplifier to mute. Since the power dropout is 10ms, time to mute is crucial. The nMUTE pin normally floats up to ~7V, but if I put a voltage clamp on it so that it does not rise above 5.8V, mute time is reduced to <1ms.
    Is there any recommended way to reduce the time to mute to less than 1ms?
  • 0 in reply to David Edmondson
    TI__Mastermind 45085 points

    Hi David,

    You are correct.  It will take 20ms to mute by pulling the /MUTE pin low.  It is not recommended to clamp the /MUTE pin to 5.8Vdc. 

    The /Standby pin can be pulled low, but it will take 4.5ms to shutdown.  This is the fasted shutdown available on the TAS5424C-Q1.