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DP83867IS: Misleading Power Sequence Diagram in the Datasheet & Dismatch with older versions

Part Number: DP83867IS

Hi!

my customer uses DP83867IS and has questions on the sequencing, this is the dedicated snap of the datasheet:

Is the diagram showing power up or down?

For power up, it would make not so much sense.

Also, to the old diagram, there is a discrepancy as well, if it shows power up.

Kind regards,

Marion

  • Hello Marion,

    "When operating in three-supply mode, the 1.8-V VDDA1P8 supply must be stable within 25 ms of the 2.5-V VDDA2P5 supply ramping up."

    This indicates the figure shows power-up.

    This is what the figure and table are showing.

    I am not sure if I am answering your question. Please let me know if there is any further classification needed.

    Thanks,

    Vibhu

  • Hi Vibhi,

    the older datasheet describes, that the 1.8-V VDDA1P8 must be supplied first!

    The design is finish, so what would be the impact for my design?

    What does the yellow marked sentence mean in the post from Marion? If the 2.5-V power....

  • Hello Dr. D,

    The note means that if the 2.5 V rail is only supplied to DP83867 devices then the 1.8 V can ramp before the 2.5 V.

    Are there any other parts supplied from the 2.5 V rail?

    Thanks,

    Vibhu

  • Hello Vibhu,

    thats not clear for me!

    The datasheet diagram descibes that the 2.5V must be powered first.

    And now you describe, that if only 2.5V are used, the 1.8V can ramp up before 2.5V???

    If I have only 2.5V, I do not have 1.8V.

    Is the powering order changed to the old datasheet or not?

    Regards

  • Hi Vibhu,

    can you please answer the customers question?

    I am also confused on the power up sequencing.

    Can you describe separately for the cases of having 1 or 2 supplies what would need to ramp up with what specs and if that changed from the old datasheet or not?

     

    Kind regards,

    Marion

  • Hello Dr. D & Marion,

    There is no requirement for the sequence of the supplies when operating in two-supply mode.

    In three supply mode there are two scenarios:

    1. When the 2.5 V power rail is used to supply ONLY DP83867 devices in your system. In this case the 1.8 V supply may ramp up before the 2.5 V supply. This is what the note describes in the datasheet.
    2. When the 2.5 V power rail is used to supply other devices in your system. In this case the 1.8 V supply must ramp up after the 2.5 V supply within 25 ms as shown in figure 31.

    Yes there are changes between the 2015 datasheet and the current datasheet.

    Please refer to the current datasheet moving forward: https://www.ti.com/lit/ds/symlink/dp83867is.pdf

    Thanks,

    Vibhu