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.
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 :-( On 24 February 2014 22:14, <[email protected]> wrote: > John Syn <[email protected]> wrote: > > >"Steady state max. voltage at all I/O pins" > > >"-0.5 volts to IO supply voltage +0.3 volts" > > > > > >So, even with power off, some voltage *is* allowed and in fact it > > >should be fairly easy to keep the voltage within these limits using > > >Schottky diodes for clamping. > > Schottky diodes aren¹t going to clamp the voltage to this range. Simply > > use the 3V3 output from the BBB to enable the supply to your board. > > > ??? > > How would using the 3.3v IO output from the BBB be any different from > clamping the input voltages to the 3.3v IO output from the BBB? It's > the same thing surely? > > One Schottky diode prevents the voltage going below 0.3 volts (it will > conduct such that the voltage doesn't go below 0.2 volts), another can > clamp the input to prevent it going above the 1.8 volt ADC supply > voltage. > > -- > Chris Green > · > > -- > 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. > -- Cheers Peter -- 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.
