ADC Fluctuation in K22F microcontroller

[prasannanaik]

Hi,

   I am using FRDM K22F board for evaluation of ADC. I have configured a FTM timer at 625 usec. In ISR of FTM, i am triggering ADC using software trigger. Input voltage is DC 1.64V (No fluctuation observed on DSO) but there are fluctuations in ADC output as seen in "ADC.xlsx". Why is there so much fluctuation even when the input is stable. I am using baord's supply as VREF.

I have even tried long sampling mode with 24 clock cycles but still getting the fluctuation.

I have attached code for reference.

Please help in resolving the issue.

Thanks and best regards,

Prasanna

[Robin_Shen]

Hi Prasanna,

Would you please check the reference-voltage noise(VREFH)?

The digital peripherals may influences ADC due to the bad design of analog power supply.(for example: I can see you toggle IO during ADC sample.)
The design of analog power supply on FRDM-K22F is not recommended.

For more detail, please refer: AN5250 How to Increase the Analog-to-Digital Converter Accuracy in an Application

Best Regards,

Robin

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