Electronic – DC/DC converter in parallel with analog circuit

The output impedance of 32 kohm can be a significant problem when attached to the ADC input on the MCU. Table 24 entitled "16-bit ADC operating conditions" states that the input impedance is typically 2 kohm and this will screw up any measurement from a source that has an output impedance of 32 kohm.

You might get away with a parallel capacitor - the sensor data sheet specifies there must be a minimum of 4.7 nF on the sensor output so have you done this? Alternatively you might need an op-amp buffer.

The table in the question suggests that you might be using a PGA in front of the ADC - please confirm that you have enabled this because it makes things easier but you will still need a 4.7 nF capacitor and normal decoupling across the power rails.

Reading further down the PGA table suggests that the analogue source impedance should be typically 100 ohm and this is way lower than what the ADI device is. I think a buffer might be a good idea.

What you've actually made between your signal line & your AD8676 in the second diagram is a "pi attenuator."

While a pi attenuator could actually be used quite well in this instance, I think yours has the wrong resistor values.

Here's a link to a calculator made specifically for making impedance-matched pi attenuator circuits like that: Pi Attenuator Calculator

using that calculator, if your op-amp had an input impedance of 50ohms, the following would work:

^{simulate this circuit – Schematic created using CircuitLab}
Since, however, the input of the OA is closer to 1Mohm than 50ohm, you'll probably want to do a little checking on "Impedance Matching Pi Networks" if you need to avoid reflections on the incoming signal cable.

Or, if we stop over-complicating things on ourselves, using the fact that the op-amp's input can be considered infinite-impedance, compared to the 50-ohm required load, you could use this even simpler circuit:

^{simulate this circuit}