[sdiy] Overvoltage input protection

[Dave Manley]

James Dunn wrote:
> Hi,
> 
> I'm currently looking at Tom Wiltshire's pic based VCADSR and was 
> wondering how to protect the input pins of the 16F684 from 
> overvoltage..? Checking the archives, the solution seems to be two 
> schottky diodes; one from input to 5v supply and one to ground.
> 
> Is this the best/correct way of doing it?

Looking briefly at the data sheet it appears the inputs are protected, 
and spec'd for an input clamp current of +/-20mA for Vi<0 or Vi>Vdd. 
This implies the part has protection diodes, and I think you can skip 
the external diodes if you add a series resistor to limit the current to 
less than the clamp current.  You'll also want to add a series output 
resistor on the opamp output.


-Dave