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TAS5424 high current surge when switched to play mode

David Edmondson
Prodigy 60 points
Other Parts Discussed in Thread: TAS5414C-Q1, TAS5414

Hi,

My design uses a TAS5424 with +15V supplied by a LT8614 4Amp regulator.  Decoupling is a total of 1680uf.

When the device is switched into PLAY mode it reports an under-voltage on the charge-pump and AVDD.

The +15V has briefly dipped to +5V for about 30ms.

It seems like the LT8614 regulator is current limiting due to the high surge current of the TAS5424.

I tried adding a further 5000uF to the +15V but this only reduced the dip to 15ms.

Is there anything I can do to reduce the high current surge please?

Best regards....David

  • 0
    TI__Mastermind 45085 points

    David,

    Are you using the TAS5424?  This device is not for new designs.  I highly recommend using the TAS5414C-Q1 device.

    The power supply regulator is much too small for this amplifier.  Even if you had been able to turn on, the current draw at normal audio performance would shutdown your regulator. 

    You should run load diagnostics to make sure the amplifier is not trying to turn on into a short circuit, as this can cause the same type of turn on problem you are seeing. 

  • 0
    Prodigy 60 points
    Hi Greg,
     
    Thanks for your reply, I will investigate the TAS5414.  Does the TAS5414 have a lower turn-on surge?
    The maximum output is less than 15W per channel, nominally 10W.
     
    For testing I have put 47R loads, there are no shorts reported by the diagnostics.
     
    Best regards….David
     
  • 0 in reply to David Edmondson
    TI__Mastermind 45085 points

    Hi David,

    The TAS5414 does not have a input surge current.  Is your output filter designed for 47 ohm loads?  If not, there will be a very high peak in the high frequencies.  This could cause the TAS5414 to oscillate.  Always use the load for which the load is designed.  This will also the amplifier and the output filter to behave as expected.

  • 0
    Prodigy 60 points
    Hi Gregg,
     
    The design I am trying to debug has got Wurth 744 870 100 dual power chokes in the output filter.  Are these suitable for the TAS 5424?
     
    Best regards….David
     
  • 0 in reply to David Edmondson
    TI__Mastermind 45085 points

    David,

    The inductor is a coupled inductor.  This will not work on the TAS5424.  The inductors cannot be coupled.  You will need to change the inductor to an uncoupled type or individual inductors.

  • 0
    Prodigy 60 points
    Hi Gregg,
     
    Many thanks for your help, as you suggested, I changed the inductors to individual types and everything works correctly now.
    (Incidentally, the fault condition was high current casing the supply regulator to current limit at turn-on).
     
    In an earlier email you suggested that I should not be using the TAS5424 for a new design and should change to the TAS5414 device.
    Is this because the TAS5424 is going to be made obsolete?
     
    Best regards….David
     
  • 0 in reply to David Edmondson
    TI__Mastermind 45085 points

    Hi David,

    I am glad to read that the problem has been solved.  This is a common error when choosing an inductor.

    The TAS5424 has been obsolete for many years.  I suggest going to the TAS5424C-Q1 four channel amplifier.  This is our latest version of this family of amplifiers.