--- In "j.chitte" <> wrote:
>
> these op-amps have an output swing from low rail to high rail - 1.5V. Sort of
> half R2R. At they can source 40mA but only sync 40uA.
>
> If I understand the MAX197 in unipolar mode (I'm using 0-5V) it does an
> internal offset. The input is floating arount 2.5V . If I feed a signal of
> 0.5V that means my op-amp needs to sink 2/20k= 100uA.
>
> Is that incorrect?
>
> thanks for your reply.
>
checking this again with a DVM I note that the op amp output is not coming down
to match the input. With input around 0.06 to 0.11 V the ouput is at 0.365V .
Once the 197 samples the output drops to what it should be and hence the
subsequent ADC reads are OK.
After about 45s without sampling the op-amp goes bad again.
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