I use zener diodes in my design for protection. cant do too much to protect the processor.
On 12/1/2014 4:47 PM, Curt Carpenter wrote: > Hello Craig and Gerald. > > Thank you again for the inputs. Would still really, really like to > get a peek at the input protection (if any, ESD or otherwise) provided > on the ADC pins as the only sure way of feeling comfortable with > this. I understand that the ADC inputs are high impedance within the > recommended operating region, but are you saying that these pins feed > directly into an unprotected FET gate or something of that sort? > > I'm using the AM335x data sheet SPRS717G revised June, 2014 and find > the following in table 5-1, p. 79: > > "Steady State Max. Voltage at all IO pins(8) -0.5V to IO supply > voltage + 0.3 V" > > also > > "Transient Overshoot and Undershoot specification at IO terminal > --- 25% of corresponding IO supply voltage for up to 30% of > signal period" > > I think I'm hearing you say that the ADC inputs don't qualify as "IO > pins" here though -- so I'm at something of a loss. The "steady > state max. voltage" spec seems to imply some sort of diode clamping. > > And the 1.8V issue aside, what happens if an ADC pin goes below ground > for a short period? Poof? > > Agree that it would be best to ban transients altogether, but I > haven't found a way to do that here yet :-) > > > > On Monday, December 1, 2014 4:38:12 PM UTC-6, Craig Markwardt wrote: > > > For ADC power supply, the AM335x datasheet lists VDDA_ADC > recommended operating range as 1.8v +/- 5% (Table 3-12), and > absolute max as 2.1v (Table 3-1). > > For ADC signals inputs, the max range is listed as 0-VDDA_ADC > (Table 3-17), so it should not exceed the input power supply > level. No tolerance is given! > > I have rev F of the document (Apr 2013), table numbers may have > changed in later revs. > > Craig > > > > On Monday, December 1, 2014 3:54:15 PM UTC-5, Curt Carpenter wrote: > > Hello Gerald > > Thank you for the input. > > I understand that the design nominal is 1.8V given the > subsystem's supply voltage, but am concerned about transients > which may exceed this, or drop below 0V.The data sheet, p. 79, > "Steady State Max Voltage at all I/O Pins" says that the > limits are -0.5V to supply voltage + 0.3V. Given that the ADC > supply (nominal) is 1.8 volts, wouldn't this place the min. > and max at -0.5 to 2.1V? What is the current limit on the > ADC pins within these limits? Is there anywhere I should > look to get some insight into the actual ADC input circuitry > re. input protection and configuration? > > Thanks, > Curt > > On Monday, December 1, 2014 2:13:17 PM UTC-6, Gerald wrote: > > Max is 1.8V. > > Gerald > > > On Mon, Dec 1, 2014 at 2:11 PM, Curt Carpenter > <[email protected]> wrote: > > > Does anyone have an electrical model/schematic for the > Beaglebone ADC inputs? Can anyone point me to the > absolute max/recommended operating conditions for > these inputs in the data sheet or elsewhere? I've > looked, but can't seem to find the data, although I > suspect that it's there somewhere! > > Thanks. > -- > 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/d/optout > <https://groups.google.com/d/optout>. > > > > > -- > Gerald > > [email protected] > http://beagleboard.org/ > http://circuitco.com/support/ > > -- > 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] > <mailto:[email protected]>. > For more options, visit https://groups.google.com/d/optout. -- 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/d/optout.
