adc value fluctuation for same input

[lijofrancis]

dear sir

i am using k40 controller.From this i am using internal adc...i am using 16 bit adc mode ..but the value is reading fluctuating and there is 50 count difference between adjacent values that may be plus or minus difference..............so please tell me how to solve this problem

[isaacavila]

Hi Lijo,

There are specific hardware considerations to ensure ADC's configuration is correct, for example:

•          Reference voltage and supply voltage should come from low-impedance source, and this usually means sufficient number of ceramic decoupling capacitors close to Microntroller's pins.

•          Signal source for ADC should also be sufficiently low-impedance. If signal is slow varying, a capacitor (tens of nanofarads) at the input of the ADC should be sufficient.

(you can consult it in https://community.freescale.com/message/78474#78474)

After achieve these hardware considerations, there is also a calibration sequence that decreases error measurement on ADC’s module.

This calibration sequence is expressed on K4x reference manual.

If both considerations are met, ADC’s reading should be right and without fluctuations.

Attached you can find a KDS project where voltage from potentiometer on TWR-KL46Z48M is read and fluctuations are less than 8 counts.