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DAC5681 or DAC5681Z Power Sequencing

pjaszkowiak
Prodigy 20 points
Other Parts Discussed in Thread: DAC5681Z

In the datasheet for the DAC5681Z, there is a note for power sequencing.  This note recommends that the 1.8V rails come on simultaneously and that the 3.3V rails do the same afterwards.  In my application, it will be very difficult to get these rails timed exactly, so I would like to know how much leeway I have the timing of these rails.  If there is some amount of leeway in how closely together the rails need to come up, then it will greatly simplify my design.  Thanks for any help.

  • 0
    TI__Genius 17340 points

    Hello,

    I don't have specific data on what kind of leniency there is on these recommendations.  From my experience, if its not too much time you probably aren't going to do any harm to the device, but of course I'm not guranteeing anything. Generally, as noted below the "absolute maximum ratings" table, exposure to these maximum ratings "for EXTENDED periods may affect device reliability".

    The better way for you to accomplish this is to have a single 1.8V supply that feeds both DVDD and CLKVDD and isolate each using ferrite beads.  Same with the 3.3V supplies for AVDD and IOVDD.  As an example, see the schematic for the DAC5681Z EVM in the users guide (http://www.ti.com/litv/pdf/slau236a) on page 41.  You'll see that we use a single 1.8V supply and feed DVDD and CLKVDD from this supply with ferrite beads to isolate them (FB5 and FB7).  Same with the 3.3V supply.  This is the recommended strategy and it has worked well for us in the past on this EVM and many others. This should be an easier solution (and cheaper) than having to worry about power sequency 4 supplies versus only 2.

    Regards,
    Matt Guibord