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How to evaluate the deviation in reference voltage of ADC?

Question asked by vijay padmanabhi on May 9, 2019
Latest reply on May 27, 2019 by vijay padmanabhi

I am using MPC5746C. The issue is that ADC reference voltage applied at pin " VDD_HV_ADCx " of micro is not exact 5V. there is slight deviation of  ~50mv (which is quite normal from HW point of view as the SBC that we use to provide VCC has typical tolerance of  2%)

However, this affects the conversion results.

For instance,

With Ideal Vref of 5 V; for input voltage 4.5 V one should get 920 ADC counts (for 10 bit ADC)

With  real Vref of 5.05 V; same input voltage of 4.5 V gives us  911 ADC counts (for 10 bit ADC)

 

This of difference 9 counts results in a large error in calculation of sensor resistance that we have connected on this ADC channel.

 

So is there any way to evaluate this deviation in Vref through SW so that we can compensate the ADC count values accordingly.

Off course, we can manually calibrate the ADC in our End of Line by giving some known voltage . However I would like to know if something can be done Automatically, through Software.

Pls advice.

Thanks!!

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