[sdiy] CV input op-amp circuit

[Vladimir Pantelic]

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?
>>
>>
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