[sdiy] CV input op-amp circuit

[Richie Burnett]

Yes, if you drive the protection diodes with too much current, you can end 
up causing a significant voltage drop across the chip's bond wires.  This 
means that ground (0 volts) on the silicon die isn't the same as ground (0 
volts) in your circuit.  Then you get errors in your ADC measurements.

-Richie,


-----Original Message----- 
From: Vladimir Pantelic
Sent: Saturday, December 5, 2020 12:07 PM
To: synth-diy at synth-diy.org
Subject: Re: [sdiy] CV input op-amp circuit

I had one 3.3V STM32 design where the SPI MISO came from a 5V IC and I 
missed
that. Each time MISO went high the internal protection diodes of the STM32
kicked in, but that in turn wreaked havoc on the internal V_ref of the ADC
making the readings more or less useless. YMMV

On 2020-12-05 13:00, Tom Wiltshire wrote:
> Yes, I agree.
>
> Didier’s question was specifically about PICs, as was my answer, since 
> that’s what I have experience with. With other chips, you’d need to check 
> the datasheet to see what there is in the way of protection and what 
> series resistance the ADC can cope with.
>
>
>> On 5 Dec 2020, at 05:33, Brian Willoughby <brianw at audiobanshee.com> 
>> wrote:
>>
>> It works so long as there is a protection diode somewhere, connected to 
>> the supply reference (ground). As mentioned, *most* uP chips have these, 
>> but it's always a good practice to check the data sheet for the 
>> "equivalent circuits" for input pins.
>>
>> Brian
>>
>>
>> On Dec 4, 2020, at 13:39, Tom Wiltshire <tom at electricdruid.net> wrote:
>>> Yes, the series resistor limits the current flowing when the input 
>>> voltage goes above the uP’s supply voltage (or above the supply voltage 
>>> plus whatever the diode drop is in this case - fairly low, iirc).
>>>
>>> So it works for negative inputs too.
>>>
>>> Tom
>>>
>>> On 4 Dec 2020, at 21:07, Didier Leplae <didierleplae at yahoo.com> wrote:
>>>> How dangerous is it to have negative voltage going to the 
>>>> microcontroller’s pins? I’ve read that it is to be avoided, but I seem 
>>>> to have done it plenty of times without frying my pic chips. Would the 
>>>> series resistor also protect against that?
>>
>>
>> _______________________________________________
>> Synth-diy mailing list
>> Synth-diy at synth-diy.org
>> http://synth-diy.org/mailman/listinfo/synth-diy
>> Selling or trading? Use marketplace at synth-diy.org
>
>
> _______________________________________________
> Synth-diy mailing list
> Synth-diy at synth-diy.org
> http://synth-diy.org/mailman/listinfo/synth-diy
> Selling or trading? Use marketplace at synth-diy.org
>

_______________________________________________
Synth-diy mailing list
Synth-diy at synth-diy.org
http://synth-diy.org/mailman/listinfo/synth-diy
Selling or trading? Use marketplace at synth-diy.org 


-- 
This email has been checked for viruses by AVG.
https://www.avg.com