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DAC3174: Power sequencing

Philipp Burch
Prodigy 130 points
Other Parts Discussed in Thread: DAC3174

Hello everyone,


I'm designing a board with a DAC3174 dual-channel DAC and am currently a bit unsure about power sequencing requirements:

1. The abs max ratings state that the difference between CLKVDD18, DIGVDD18 and VDDA18 must not be more than 0.5V, so these should be connected together with at most some passive isolation circuitry, correct?

2. Are there sequencing requirements between VDDA18 and VDDA33? I.e. is it necessary to somehow link the two voltage regulators to make one rise after the other?


3. What about IOVDD? Is it safe to have IOVDD powered while the rest of the DAC is not?

Thank you. Best regards,
Philipp Burch

  • 0
    TI__Mastermind 29220 points

    Hi,

    I have forwarded this question on to our design team, and will wait for their response.  It does appear that the three 1.8V supplies (VDDA18, DIGVDD18 and CLKVDD18) would have to rise together to meet the absolute max specifications table.  This hasnt been an issue on our EVM as we generally have a single voltage regulator to generate the 1.8V supply and then separate out the various voltage domains with ferrite beads.  You may have separate voltage regulators and if so then this may be an issue.  I would have to assume that these supplies should power up together unless I hear otherwise from design.  The abs max specs table makes me think there could be ESD protection circuits that could get turned on if there is too much difference between the three 1.8V supplies.

    The 1.8V supplies would not have any requirements in relation to the 3.3V supply or the IOVDD supply as these different pins could not have any ESD circuitry between them that could get turned on by a voltage mismatch, since these supplies can all be different voltages anyway.  So no requirement for one supply to be on before or after another, and that would extend to the IOVDD as well.  It can power up and be up before the others.

    Regards,

    Richard P.

  • 0 in reply to Richard Prentice
    Prodigy 130 points
    Hello Richard,

    thanks for your quick response! Have you already got any confirmation from the designers? I suppose that it is exactly as you mentioned, but I'd rather be sure that there really is no sequencing requirement between the different voltage levels. It's not only about internal ESD protection diodes, but also about what the converter does when only part of the supply is on. In any case, I'll take care to keep !RESET and TXENABLE low during startup, so that the output *should* stay quiet.

    Regards,
    Philipp