Problem with reading the voltage divider sensor

[JohnRob]

@boys_always_cry

I find that the ADC value starts to fluctuate and is unstable when I give the converter a duty cycle of around 40% or above. but strangely this ADC fluctuation does not occur on the output side regardless of the duty cycle value that I give.

Off hand I would suspect the input to your converter has more noise than the output. I would suggest you add a 0.1µF capacitor at the instrumentation side of the divider.