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Original question:

DAC5675A: Power Sequencing

DAC5675A-SP: Power-down sequencing

David MURAT
Prodigy 20 points
Part Number: DAC5675A-SP
Other Parts Discussed in Thread: DAC5675A

Hi,

Our electronics exhibit at least 4 components that need a power-up sequencing, including the DAC5675A-SP.

Most of the power sequencing constraints are only related to the power-up sequence and it is more difficult to design the power-down sequence because we have to take into account an untimely power failure.

Is the sequencing constraint between AVDD/DVDD on the DAC5675A-SP relevant for the power-down sequence ?

Best regards,

David

  • 0
    TI__Guru* 91947 points

    David,

    After consulting with the design team, they mentioned there are no power sequence implications for the DAC5675A.

    Regards,

    Jim

  • 0 in reply to jim s
    Prodigy 20 points

    Hi Jim,

    You mean no power-down sequence ?

    AVDD and DVDD still need to be powered-up at the same time (AVDD-DVDD < ± 0.7 V) ?

    Kind regards,

    David

  • +1 in reply to David MURAT
    TI__Guru* 91947 points

    David,

    There are diodes between the AVDD & DVDD supplies.  If you exceed +/-0.7V the diode will be forward biased.  We don’t think there are any reliability issues (if only our DAC is on the supplies), but if AVDD ramps down to 0V while DVDD=3.3V then the voltage on the AVDD supply will be approximately 2.6V.  This means that any AVDD~2.6V supply current will conduct through our internal diodes from the DVDD supply.  This could have implications for other parts on the board if the supply is shared.

    Regards,

    Jim

  • 0 in reply to jim s
    Prodigy 20 points

    Hi Jim,

    Thanks for the details. If I understand well, there is no problem at power-down if all supplies are switched-off at the same time or if an untimely power failure occurs.

    In our electronics, AVDD and DVDD are shared with other parts and we need to make a proper sequence at start-up for the other power rails.

    AVDD and DVDD power-up is specified in such a way that they ramp-up at the same time after all other rails are established.

    We will then switch-off all the power supplies at the same time.

    Best regards,

    David

  • +1 in reply to David MURAT
    TI__Guru* 91947 points

    David,

    That is correct. Your sequence all appears fine.

    Regards,

    Jim