Peter Washington <[email protected]> wrote: > [-- text/plain, encoding quoted-printable, charset: ISO-8859-1, 68 lines --] > > It MAY, and I stress the MAY, be safe to allow voltages between -0.5 and + > 0.3 Volts to appear at the I/O pins of the AM355x processors when they are > not powered up, but using schottky diodes to keep them to within +0.3 volts > of an external 3.3 supply rail WILL fry them. > You've misunderstood me, I'm going to clamp to the BBB's 3.3 volt I/O supply.
> The suggestion made above was to use the presence of the 3.3 V supply on > the BBB to Enable / Switch the external supply On, or conversely the > absence of the BBB 3.3 Volt supply removing or disabling the external 3.3 > Bolt supply. > > Has this made it clearer ? I do hope so, I hate it when the Magic Blue > Smoke escapes from a chip :-( > That's a possible way of doing it but I don't like the extra complexity, it's another way for things to go wrong. If that 'logical' connection between the BBB's 3.3v IO supply and my external supply goes wrong then the inputs get fried. I prefer simply using the BBB's 3.3 IO supply *directly* (with a diode of course) to clamp the inputs. We're talking about very small current here, I'm aiming to have 10k (or more maybe) series resistors in the inputs so the current through the diode even with a 3.3 volt difference between input signal and BBB input it's only 300 microamps or so. -- Chris Green ยท -- 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 [email protected]. For more options, visit https://groups.google.com/groups/opt_out.
