Well, I think there is a better way that relying on luck. I suggest you take a look at http://www.elinux.org/Beagleboard:BeagleBoneBlack#Expansion_Header_Pin_Usage
Gerald On Sat, Sep 5, 2015 at 7:51 PM, rattus <gehlv...@gmail.com> wrote: > I went with a little LDO to provide a local 3.3V source; looks like it'll > pop up in about 50-100uS after 5V is available. > > Thanks again. > > > On Saturday, September 5, 2015 at 12:22:21 PM UTC-6, Graham wrote: >> >> I think the VDD_3V3B rail is deliberately held off until the unit has >> started booting, >> and has already read the boot instructions. It is not a rise time issue. >> I suspect it was done deliberately to help with the "don't drive the rest >> of the pins" issue. >> >> A little 5V to 3.3V regulator to power your LVC "input" IC will work >> nicely. >> Provided that it is powered at the same time the BBB is. >> That is, use VDD_5V if powered from the power jack. >> >> Relative to power appearing at the power jack: >> SYS_5V is delayed 50 ms. >> VDD_3V3B is delayed 100 ms. >> SYS_RESETn is delayed ~130 ms. >> >> I have not measured power supply sequencing when powered by USB. >> >> Or if you are dealing with both I and O on the boot pins, use something >> like >> a 74CBTLV3126 bus switch / transmission gate to isolate your circuitry >> from the BBB while it is booting. Just make sure the bus-switch / >> transmission-gate >> is powered while the BBB is booting. >> >> This issue only comes up about once a week here on the forum. :-) >> >> --- Graham >> >> >> -- > For more options, visit http://beagleboard.org/discuss > --- > You received this message because you are subscribed to the Google Groups > "BeagleBoard" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to beagleboard+unsubscr...@googlegroups.com. > For more options, visit https://groups.google.com/d/optout. > -- Gerald ger...@beagleboard.org http://beagleboard.org/ -- For more options, visit http://beagleboard.org/discuss --- You received this message because you are subscribed to the Google Groups "BeagleBoard" group. To unsubscribe from this group and stop receiving emails from it, send an email to beagleboard+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
