I am using a STM32L051C8. In my circuitry there is an OPAmp's output leading via a 2k2 resistor to an input of the STM-chip which is configured as ADC input. The STM-chip is supplied by 3.3 V and the OP by 5 V, rail-to-rail.
As long as the OP's output voltage is below 3,3 V everything is okay. Slightly above 3,3 V I still get values of 4095, but from 4 V on or more the ADC-values are decreasing again, about 3800 or so.
Is my resistor with 2k2 to small to keep the limit under 4095? Or how can I maintain a limitation without supplying the OP by 3.3 V?