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DAC7728: Power Sequencing

Edward Lefferd
Prodigy 70 points
Part Number: DAC7728

Will the DAC7728 work properly if it is not brought up in the sequence outlined in the datasheet? I am having a problem with being able to sequence the AVss rail as it automatically comes on. The datasheet says the digital initialization pins need to be well defined before the digital supply comes up, but is there any reason why the AVss rail needs specific sequencing? 

Also how much time should there be between each rail in the sequence?

  • 0
    TI__Guru 53573 points

    Hi Edward,

    Welcome to the E2E forum!

    I was able to speak with our designers for this park to get a better understanding of the supply sequencing of this device. The most critical portion of the sequence is:

    1. DVDD/IOVDD comes up before AVCC/AVDD.  They specifically recommended that DVDD be at least 3V before the AVCC starts to ramp.  Otherwise, there is not really a time limit between the supplies ramping.  

    2. The DVDD/IOVDD supply has at least 75mA of drive capability.  When the device is starting up, it will pull a higher current for a very short duration.  If the supply cannot source this momentary current there is a chance that your supply will collapse, which will then cause a brownout event in the device.

    They do not see any issue with the VSS supply ramping first, but they recommend that you verify the drive capability of DVDD just to be extra safe. 

    Hope that solves your issues,

    Thanks,

    Paul