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.
