IMX7D ADC offset issue

[frankyhsu]

Hi

We measure the ADC input voltage and read the ADC value in kernel. The input voltage is changed by thermal NTC. We found we will have a voltage difference about 0.032~0.048V between ADC read and voltage measurement. How to decrease difference between them? The drift seems to be too much.

[igorpadykov]

Hi Franky

one can check stability and noise of adc power : VDDA_ADCx_1P8, VDDA_1P0_CAP.

If voltage difference is constant, it may be removed by software.

Also may be recommended to check ground lines for thermal NTC and adc,

they should be connected in one point. Note, this is applicable to performing measurements too.

Best regards
igor
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[frankyhsu]

Which ground is meant for ADC ground line to connect to NTC ground?

[igorpadykov]

could you short NTC to check if drift will remain

Best regards
igor

[frankyhsu]

We have the connection as below since we hope to have a clean power so we use 1.5V LDO from PMIC. Will the different power source affect the power accuracy?

[igorpadykov]

>Will the different power source affect the power accuracy?

no

Best regards
igor