[sdiy] CV input op-amp circuit

Roman Sowa modular at go2.pl
Mon Dec 7 13:12:56 CET 2020

Yes, they will, after all they are Schottky diodes. And if you put a 
resistor after the diodes to the input of IC, even 1k or less, the clamp 
current inside the IC will exceed limiting value only when BAS diodes 
will burn open.

As for supply absorbing current spikes from input via diode - this is 
not low impedance input, so thanks to input resistor the current can be 
easily eaten by regular circuit load.


W dniu 2020-12-07 o 12:56, Richie Burnett pisze:
> 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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