Hi James,

It's worse than that. I read the allowable analog input voltage range (CH0 =
& CH1) is=20
from Vss to Vdd, single ended, or perhaps an extra +100mV each way in case =
of=20
pseudo-differential mode (whatever that is). You're not meant to operate it=
=20
anywhere close to making the internal protection diodes conduct. I see wher=
e you=20
get the 0.6V from, but you have to follow the * and read the fine print.

In practice though there's only so much you can do. Typically some series R=
 plus=20
Schottky diodes to suppply rails will keep things with +/-0.3V above and be=
low the=20
supply or there abouts. That's some distance away from the absolute maximum=
s,=20
but note still technically outside of the operational range. Depends on the=
 conditions=20
you're designing for... eg. must survive if vs must operate properly.

Other options are reduce signal range to suit, and/or come up with some mor=
e=20
precise limiting circuitry.

Brent

On 18 May 2017 at 13:18, James Cameron wrote:

> I'm missing something terribly obvious, can anyone point it out?
>=20
> 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?
>=20
> http://ww1.microchip.com/downloads/en/DeviceDoc/21294C.pdf
>=20
> See also Figure 4-1; how to protect the diodes between the CHx pin and
> the Vdd pin.
>=20
> 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
> --=20
> James Cameron
> http://quozl.netrek.org/
> --=20
> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist
>=20



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