How can I eliminate the paralleling effect of ADC input impedance at the output of sensor sense resistor?

Question

I am using a sensor that gives 5V output However, the ADC I am using can sense only a 3.3V at absolute maximum. A very simple way of translating a 5V to 3.3V was to use a voltage divider as shown. However, the resistor R2 comes in parallel with ADC equivalent impedance and so the overall ratio of voltage divider changes. How can I solve this problem? P.S I don't know the equivalent impedance of ADC and none is provided in datasheet

One solution I found was to use an op-amp between ADC and R2 as then R2 will be in parallel with op-amp input impedance which is infinite ideally and so problem will be solved. But I don't know if it'll work. Will it work? If not then what is the solution?

Also I am completely open to other ways of translating 5V output to 3.3V ADC input. Thanks

^{simulate this circuit – Schematic created using CircuitLab}

Answer 1

The input impedance of many ADCs is so high that it can be ignored and doesn't affect the result provided the resistors are not too high (ie <10k ohms).

It is often beneficial to put a capacitor from the input of the ADC to ground to provide the charge needed when the ADC performs a sample. A value such as 0.1uF ceramic is suitable if the signal is not rapidly changing. As Kartman comments, it is also useful to filter out high-frequency components such as noise.