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A question in ADS6424

aongkun
Prodigy 130 points
Other Parts Discussed in Thread: ADS6424, ADS6445

Hi,

      Now I use ADS6424, when I set parrallel config pin: CFG1 CFG2 CFG3 CFG4, in pin assignments part of datasheet(page 25) these four pin is related to AVDD, but in page 15 these four pin is related to LVDD, can you tell me which one is corret?

Bill

  • 0
    TI__Mastermind 29220 points

    Hi,

    Page 15 describes the voltage to be set on the configuration pin as a fraction of LVDD, and that is how we have set up our evaluation module for these devices as well - with a set of resistors making a voltage divider between LVDD and ground.   The input buffers on these pins have thresholds set up internally as a fraction of LVDD to determine which of four choices the input is set to.  But since AVDD and LVDD are both nominally 3.3V, if you were tie one of the pins to AVDD as mentioned on page 25 then that would not be a problem.  But probably page 25 would be better changed to say tie to LVDD rather than AVDD.

    By the way, this datasheet also is in need of another edit in relation to the voltages for the CFG pins.  Please see the datasheet for the ADS6445 which has already had this page corrected.  The CFG pins should *not* be set to 0V, 3/8LVDD, 5/8LVDD or LVDD - they should be set to 0V, 1/2LVDD, 5/6LVDD or LVDD as described in the datasheet for ADS6445.  This needs to be fixed inthe ADS6424 datasheet.  It turned out that the threshold voltages on the CFG input buffers were high than intended.

     

    Regards,

    Richard P.

  • 0 in reply to Richard Prentice
    Prodigy 130 points

    Hi,   Richard

            Thanks for your response. If connect these pin to AVDD, I think the function is ok. But whether the precesion is affected? Because the AVDD and the LVDD are isolated. Your mean that the CFGx should be connect to LVDD, the page25 is incorrect?

            Thanks very much

    Bill

  • 0 in reply to aongkun
    TI__Mastermind 29220 points

    Yes, if you connect that input pin to AVDD the function should be ok.  Both supplies are at 3.3V, with some tolerance.  Since the voltage threshold for highest level of the CFG input is 5/6 of the supply, you would have to have the LVDD at 3.6V and the AVDD at 3V before there could be any issue with sensing the input wrong.  So yes, precision of the input threshold could possibly be an issue if the supply voltages were that far apart.  So it would be better if we references LVDD on page 25 but I don't think it would be an issue.  When we next revise the datasheet we can change that reference to AVDD.

    Regards,

    Richard P.