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PCM1690-Q1: VCC VDD power up/down sequence

Atsushi Hirai
Expert 4710 points
Part Number: PCM1690-Q1

Hi team,

The datasheet mentions about the VCCx VDD power up sequence as below. I understand it means customer should power on and off at VCC and VDD simultaneously but, I cannot understand which Abs max rating is limiting it.

How much voltage difference is acceptable between VCCx and VDD?

Regards,

  • 0
    TI__Guru 53663 points

    Hi Hirai-san,

    I am not sure exactly what they are referring to, as I see no limitation from the abs. max. table either.  Here is my interpretation of why you would want to avoid ramping VCC significantly later than VDD:

    VCC is used to derive the VCOM voltage, which is created with just a voltage divider.  If the VCC was currently ramping and VDD was already >2.2V and I2S was being actively provided, then you could potentially the output of the DAC start playback before VCOM is at its ideal voltage.  This would mean the audio data would be clipped at the ground supply and could sound distorted.  In addition, we generally recommend a fairly large cap on the VCOM pin which must also be charged.  A long charge time could prolong the period where the output is being clipped.

    Thanks,

    Paul