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TAS5630B: TAS5630B READY signal delayed assertion

David Lambert1
Prodigy 60 points
Part Number: TAS5630B

My company has a design that has been successfully using the TAS5630B for several years.  We've built around 70 units to date with no issues.  But, recently, one of our units has a TAS5630B that is taking an unusually long time to set READY signal high following power-up.  When we apply power to this chip, shutdown signal SD goes low (i.e. chip in shutdown) and stays low for around 0.5 second.  Once SD goes high, READY goes high and the chip appears to function correctly afterwards.  In our design, we need to know how long the chip requires to be ready to transmit (worse case).  Our design waits 60ms before transmitting and this has always been more than sufficient time.  This particular unit has been working in the field for 2 years and only recently starting exhibiting this behavior.

We're trying to determine if this issue is caused by something internal to the IC or by an external component.  Does anyone have any ideas or suggestions?

  • 0
    TI__Guru 61300 points
    David,

    The SD pin going low and then High sounds to me like the PPSC check that the device first does when it starts up. As per the datasheet: "total duration of this process is roughly proportional to the capacitance of the output LC filter" and "typical duration is <15 ms/μF". Maybe your output capacitance has changed? Worth a quick check.

    Regards,

    -Adam
  • 0 in reply to Adam Sidelsky
    Prodigy 60 points

    Adam, we measured output capacitance "in-circuit" and got 1.7uF versus 1.5uF on a second functioning unit and 1.89uF on a third functioning unit.  -Dave 

  • 0 in reply to David Lambert1
    TI__Guru 61300 points

    David,

    When the problem occurs, has the unit been previously OFF and at room temp? Maybe the issue is at higher temp when the board is warm?

    If you replace the IC, does the problem stay with the board?

    Regards,

    -Adam

  • 0 in reply to Adam Sidelsky
    Prodigy 60 points
    Adam, Yes, the unit was previously off and at room temperature. This problem is repeatable. In our application, the IC isn't on very long and the heat sink stays at room temperature.

    We haven't replaced the IC yet; we wanted to check everything we could check before replacing it.

    Dave
  • 0 in reply to David Lambert1
    TI__Guru 61300 points
    Dave,

    It might be worth reheating the solder joints on the IC to make sure there isn't a cold solder or similar that's causing the issue.

    If this doesn't solve the issue I would replace the IC carefully and check if the board is causing the issue. Save the unit currently on the board.

    Send me an email at adamsidelsky(at)ti(dot)com and we can discuss further.

    Regards,

    -Adam