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
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>>>>
>>>
>>>
>>>
>>> --
>>> Gerald
>>>
>>> [email protected]
>>> http://beagleboard.org/
>>> http://circuitco.com/support/
>>>
>>
--
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