That diagram looks just like the ones in the PIC microcontroller=20
datasheets.  There's a spec for the max current those diodes can handle=20
(IIRC called clamp current), from which you can calculate the series=20
current-limiting resistor value.
Also from memory for 12V protection, I had worked out to something=20
around 400 ohms, and just use 1k on the analog input.

Cheers,
-Neil.




On 5/17/2017 11:18 PM, James Cameron wrote:
> I'm missing something terribly obvious, can anyone point it out?
>
> Assuming an MCP3002 powered from 3.3V, but an analog signal that may
> swing up to X volts, what minimum series resistance is needed given
> the maximum rating of Vdd + 0.6V?
>
> http://ww1.microchip.com/downloads/en/DeviceDoc/21294C.pdf
>
> See also Figure 4-1; how to protect the diodes between the CHx pin and
> the Vdd pin.
>
> In general, I'd be happy with a quite large resistor.  I'm just
> curious as to what the minimum would be, because I couldn't find it in
> the datasheet.
>

--=20
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