Why the narrow 12v ±5% voltage spec on the Braswell x86?

Discussion in 'UDOO X86' started by Myself, Apr 21, 2023.

  1. Myself

    Myself New Member

    Apr 21, 2023
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    I'd like to run my 2016-era Udoo X86 directly from a 12-volt battery (not in a car, so automotive noise concerns don't apply). Technically it's a 4-series stack of LiFePO4 cells, which normally sit between 12 and 14 volts, but may range between 10 and 14.5 depending on what else is happening in the power system.

    I've gone through the schematic and I just can't find anything that's so picky about voltage. All the PMICs and buck converters seem to be Richtek parts intended for laptops, with voltage ranges of:

    RT8231: 4.5v-26v
    RT8175A: 5v-25v
    RT7243: 4.5v-18v
    RT8297: 4v-17v

    Looks like as long as I stay below 17, I shouldn't blow up anything there. How about the rest of the system?

    The ESD varistor has a max continuous voltage of 18v and clamps at 24. The reverse polarity protector is good for 25. As far as I can tell, the only place the 12V_ALW rail goes other than the PMICs, is the fan header, and fans are famously tolerant.

    Soooooo.... I can't figure out where the 12v ±5% requirement comes from. That's weirdly tight, so either there's a very good reason that I've completely missed, or perhaps it was inserted as a placeholder and nobody ever actually qualified the true voltage range. (That would be a lot of work so I'd completely understand skipping it, if so!)

    Thoughts? Anybody wanna place bets on what blows up when I try it? ;)

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