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TAS6422EQ1EVM: Output Instability

Sam Marshall
Intellectual 440 points
Part Number: TAS6422EQ1EVM

All outputs are sometimes unstable (attached capture).  The part is in play mode with an input of all zeros.  No faults or warns are present. 

Sometimes the instability can be stopped with HiZ mode, or the EVM standby switch.  Other times this does nothing, and grounding a clock is the only thing that will make it stop.  The power supplies and input clocks look ok.  I2C is responsive.

Sometimes the part is producing a zero output without the instability.  Sending audio always provokes the issue.

What might cause this?

Thanks.

  • 0
    TI__Genius 9530 points

    Sam,

    As class D is a modulator based amplifier, there is out-of-band noise. Can you please measure that in a audio way: (1)applied a 20~20KHz filter between AMP and measurement equipment. If it is AP, then there is internal-built 20~20KHz filter.  (2)measure differential voltage postive-negtive.  

    Dylan

  • 0 in reply to Dylan Yao
    Intellectual 440 points

    Dylan,

    It is 11.4Vrms @ 90kHz, in a sporadic nature (see previous trace).  The input is ZERO.  Any class D switching after the filter should not be so hot, nor should it be sporadic. 

    Additionally, when giving it non-zero input data, the output is silent in the audio band (still has the sporadic hot 90kHz problem).

    Thanks.

  • 0 in reply to Sam Marshall
    TI__Mastermind 37595 points

    Hi Sam,

    I have some questions on your test setup and circuit components.  The 90kHz is the approximate cutoff frequency of the LC filter.  Do you have a load present in your testing?  If not, the LC filter will have a very high Q and can easily show noise at this frequency.  

    The interesting statement is that the output noise can be stopped "sometimes" when placed into HI-Z or Standby.  In these two states the output is not switching and cannot provide any signal to the load.  This noise you are seeing must be entering through he grounds or the power supply.  You may need to investigate the source to cause the output to have such high noise when in Hi-Z or Standby mode.. 

  • 0 in reply to Gregg Scott
    Intellectual 440 points

    Gregg,

    Power supply is the first thing I checked.

    A 5805 is working in the same setup without major issue.  I’d stick with the 5805 instead of the 6422, but the 48kHz ripple is higher than I’d like.

    Your conclusion is logical, however, the more logical conclusion is the EVM is DOA.  It is flaky, sometimes failing to shut down with HiZ or Shutdown, and never producing audio.  It is clearly inappropriate behavior.  To investigate the source, can I send you the 6422 for test and replacement?

    Thanks.

  • 0 in reply to Sam Marshall
    TI__Mastermind 37595 points

    Hi Sam,

    If it is the EVM, then something is amiss. I will contact you directly to the email address in your E2E forum account and provide instructions