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DAC5675A AVdd vs. DVdd

John Stephens
Prodigy 75 points
Other Parts Discussed in Thread: DAC5675A

Is there any electrical connection between AVdd and DVdd in the DAC5675A? eg. protection diodes, capacitors, etc.

  • 0
    TI__Guru 66104 points

    Hi John,

    The absolute maximum difference between AVDD and DVDD is rated from -3.6V to 3.6V. This indicates that there are no internal ESD diode connections between the two nets. Otherwise, the absolute difference will be limited to within typical diode drop voltage.

    There could also be some stray capacitance between the two nets, and I will need to confirm with designer on this. Could you please advise how this information will be used in your system design? Is this question related to power up/down sequencing? If so, the DAC does not require sequencing due to the spec mentioned above.

    -Kang

  • 0 in reply to Kang Hsia
    Prodigy 75 points

    Thanks for your response Kang. Here's the situation: We are using two DAC5675As in our design and have had an issue that requires some analysis. Power was applied to the AVDD at +3.3V, but the DVDD was floating at the device. Under these conditions we observed 3.3V on the analog side as expected, but only 2.5V on the digital side. There are several ICs powered from the DVDD supply so we estimate approximately 225mA flowed from AVDD, through each DAC, to the DVDD side producing +2.5V on the digital side. I am trying to determine whether that current could have damaged something inside the DACs.

  • 0 in reply to John Stephens
    TI__Guru 66104 points

    John,

    I am checking with the designer and will update you once I hear back from them.

    -Kang

  • 0 in reply to Kang Hsia
    Prodigy 75 points

    Thanks Kang. I appreciate your attention to this. Anything that can be done to expedite would also be very helpful as we are under a lot of pressure over this.

  • 0 in reply to John Stephens
    TI__Guru 66104 points

    John,

    The design team have looked into this and found the following:

    "The DAC5675A has apdiodes between the analog and digital supplies.  The datasheet should be updated to limit the voltage between the pins to 0.9 volts."

    Therefore, we believe the DVDD node of 2.5V is the correct behavior. We will need to update the datasheet to limit the absolute maximum difference between the two nodes to be +/-0.9V.

    -Kang