[sdiy] ADc & DAC voltage dividers.. fixed resistors values finally..

Roman Sowa modular at go2.pl
Wed Feb 17 09:12:18 CET 2021


All 3 opamps I listed are unity gain stable and cover full input span, 
and even beyond rails.
I also wrote about RRO and RRIO opamps in earlier post and how to 
overcome this limitation.

Roman

W dniu 2021-02-17 o 08:53, Brian Willoughby pisze:
> Yeah, one thing to look out for is that not all rail-to-rail op-amps support the full voltage on both input and output. Quite a lot of them are only rail-to-rail outputs, and assume that you'll be using some gain. Thus, a voltage follower is going to work very poorly with those select chips.
>
> Always check the data sheets carefully and thoroughly.
>
> Brian
>
>
> On Feb 16, 2021, at 23:30, Roman Sowa wrote:
>> None of them would work in this scenario.
>> My humble suggestion is to try MCP606 as "good enough". It's a tad slow but if you plan to use it only for CV sampling at 1kHz, it's still fast as lighning.
>> Or other interesting opamps: LT1637, OPA340 to mention just 2
>>
>> Roman
>>
>> W dniu 2021-02-16 o 21:50, Jean-Pierre Desrochers pisze:
>>> So far the precision opamps I have on hands are:
>>> OPA2277PA
>>> OP177G
>>> OP275G
>>> LF412CP
>>> I don't think they fit the requirements..
>>> Any ideas for a good 16 bits ADC front end opamp ?
>>>
>>>
>>> -----Message d'origine-----
>>> De : Mike Bryant
>>> Envoyé : 16 février 2021 14:52
>>>
>>>> But to me 5V rail to rail opamps will never reach 0 neither +5.0v at their output when these values show at the input..
>>>> Close values but not the original ones.
>>>> Or maybe I am wrong on that.
>>> The ones for ADCs have FET output stages so they'll happily go all the way to zero accurately and pretty near to the positive rail.  And many ADCs don't go all the way up to 5V anyway as they need some headroom for the internal op-amp on the voltage reference
>
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