topic Re: IMX7D ADC offset issue in i.MX Processors

IMX7D ADC offset issue

frankyhsu — Tue, 02 May 2017 03:07:33 GMT

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.

Re: IMX7D ADC offset issue

igorpadykov — Tue, 02 May 2017 05:46:53 GMT

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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Re: IMX7D ADC offset issue

frankyhsu — Tue, 02 May 2017 05:57:26 GMT

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

Re: IMX7D ADC offset issue

igorpadykov — Tue, 02 May 2017 10:42:07 GMT

could you short NTC to check if drift will remain

Best regards
igor

Re: IMX7D ADC offset issue

frankyhsu — Tue, 02 May 2017 12:11:33 GMT

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?

Re: IMX7D ADC offset issue

igorpadykov — Tue, 02 May 2017 15:13:39 GMT

>Will the different power source affect the power accuracy?

Best regards
igor