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66AK2G12: BOOT_RSVD Resistors

Sarah Cratem
Intellectual 815 points
Part Number: 66AK2G12
Other Parts Discussed in Thread: 66AK2G02

Hi team!

In the 66AK2G12 data sheet Rev.D, SPRSP07D, added that "separate external pull resistors shall be connected to the ball V23(BOOT_RSVD)."

I haven't see any boot up issue with 66AK2G12's internal pull-down resistor(the default after reset). What is the severity if the internal pull-down resistor is used instead of external pull-down? What is the possibility of boot up failures if there is no external pull-down?

Does this apply to all 66AK2G12 silicon revisions?

Thank you,

Sarah

  • 0
    TI__Guru* 87040 points

    Sarah, generally speaking, the internal pull resistors are very weak pulls and can vary widely across process and temperature.  I would only rely on the internal pulls if there is nothing else connected to the pin (no trace or other component). 

    I would consider bootmode pins a special case since you risk your board not booting with no workaround.  Thus, I would definitely put an external pull for all bootmode pins, especially for a production board.  As you say, you have not hit an issue, but you are probably only working with one board and under nominal conditions and temps.

    Regards,

    James   

  • 0 in reply to JJD
    TI__Intellectual 815 points

    Hi James,

    Thanks for the answer!

    We will definitely put an external pull in the future, but I want know how urgent it is to do it.

    The production boards came out more than a year ago, but I haven’t heard about any boot issue.

    If this is a high risk why it is never listed in 66AK2G02 data sheet and it's not in 66AK2G12 data sheets rev.A ~ rev.C until rev.D? Actually, it is never listed as BOOT_RSVD until rev.D. Is it changed for the newer silicon revision?

    Is this external pull just for best practice or there are reports or tests indicating the potential boot issue?

    Thanks,

    Sarah

  • +1 in reply to Sarah Cratem
    TI__Guru* 87040 points

    Sarah, is the pin connected to anything?  Any trace to another component or test point?  If not, it is probably OK, and the risk is very low that there would be a problem. Otherwise, noise coupling onto the signal may not be overcome by the weak internal pull.

    I don't have any history on issues with this signal.  There is only one silicon revision that i know of, just the datasheet has been revised.  Most likely it was missed early on and just changed to stay in line with the recommendations for all the bootmode signals.

    REgards,

    James