On 2/24/14, 2:14 PM, "[email protected]" <[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? I didn't say 3V3 IO, I said 3V3 output or 3V3 supply output (P9-3 or P9-4). If you have a regulator on your 12V side, you probably have an enable pin. Connect P9.3 to the enable pin. > >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. I'm not sure you understand how a schottky diode works. Voltage drop at forward biases of around 1 mA is in the range 0.15 V to 0.46 V, but if you conduct more that 1mA, your volt drop will be higher. Also, the reverse voltage will not clamp at all. Regards, John > >-- >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. -- 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.
