KL03 repeat adc calibration if VDDA is decreasing because of battery supply

[martinkrause]

According to AN3949 ADC calibration results are best if VDDA > 3 V. We have a system running from battery (3.3 V lithium), where VDDA decreases over time. Now we are wondering, what is better, calibrate the system once in the beginning when the battery is fresh (> 3 V), store calibration values in flash and use this values for the rest of the life-time. Or do a calibration every time the system is switched on. In the second case VDDA will decrease over time, because battery voltage decreases. The calibration is then done under the same environmental conditions as the normal ADC measurements (which I consider as good?), but with VDDA < 3 V which is not optimal according to application note.

Which way is the better way? Do calibration once when VDDA > 3 V and re-use this values over the whole life-time, or do a re-calibration on every boot?

Best Regards,

Martin

[Stano]

Hi Martin,

this MCU contains the stabil internal voltage reference 1.195V. You can use it as fix reference for all your measurements. If you measure such ADC value and VDDA - VREFH is changing, the recalculation to the fixed reference provide you excellent results, not depending on the VDDA (battery) voltage. I have proved this method and works well.

Best Regards,

Stano.

[jeremyzhou]

Hi Martin,

Before start the ADC sampling operation, the ADC prior to be calibrated under no matter the voltage of the battery surpass the 3.3v or not.

However Id' like to suggest that you can use the ADC and bandage to speculate the voltage of the VDDA, it can notify you when the battery decrease tremendously.

Hope it help.
Have a great day,
Ping

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