[sdiy] CV input op-amp circuit

[Richie Burnett]

Will external Schottky diodes start to conduct before the on-die anti-static 
protection diodes?

As others have said, if you clamp external inputs to the microcontroller's 
supply rails with diodes, then be careful that you don't cause the supply 
rail to rise if the clamping current becomes significant.  The supply rail 
isn't an infinite current sink.   It can only absorb the clamping current 
either momentarily with some big decoupling capacitors, or in the 
steady-state if there is sufficient load on the supply.

-Richie,



-----Original Message----- 
From: Roman Sowa
Sent: Monday, December 7, 2020 11:37 AM
To: Mike Beauchamp ; synth-diy at synth-diy.org
Subject: Re: [sdiy] CV input op-amp circuit



W dniu 2020-12-05 o 22:42, Mike Beauchamp pisze:
>
> Regarding protecting ADC inputs, is anyone using external BAT54S schottkey 
> diodes? It seems like it might be easier to slap these in rather than rely 
> on the internal uC's diodes and the issues youve raised of sharing that 
> current if multiple pins are overloaded etc.
>

that's exactly the part I use. Among other design choices like PESD diodes.
The maximum current of input protection diodes in IC is usually 20mA,
that's clearly written in datasheets. Not that much, and with added
Schottkys the input can take much more overload without any unwanted
current wandering along tiny power traces inside the chip.

Roman
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