MPC5777 SDADC Electrical Accuracy Specification Clarification

erikkundro — Wed, 10 Jan 2018 16:33:11 GMT

Hello,

I am looking at the MPC5777 micro, specifically the built in sigma-delta ADC (SDADC). The datasheet has offset and gain error values on page 26. As I interpret these specs, it seems to imply that even with the built in calibration completed I could still expect many millivolts of offset and gain error depending on how much temperature, Vdda, Vrh_sd, etc vary or drift from the moment calibration was done last. Is this interpretation correct?

For my application I need a high degree of DC accuracy. The signal I am trying to measure is a small amplitude and slow varying signal but requires accurate DC measurement where the many millivolts of offset and gain error in the spec sheet are not acceptable. I don't need to do anything fancy with the ADC data, I just need to measure a signal to see if it is above or below a threshold but I need to know this with relatively high DC accuracy.

Can I run the SDADC calibration sequence in real time, say every second or two, such that I can constantly calibrate out the offset and gain error drift due to temp, voltage, etc? Or is the calibration something that shouldn't be done in a real world running environment with actual analog signals coming into the SDADC?

Assuming I can run calibration every few seconds to constantly eliminate any DC error in the SDADC, how accurate is the SDADC after I complete a calibration? Can I assume there is effectively no offset or gain error at the moment calibration is complete?

Does NXP have a spec for how much offset and gain can drift per degree C of temp change (i.e. delta in mV/C)?

Any other thoughts or suggestions for high DC accuracy applications?

Re: MPC5777 SDADC Electrical Accuracy Specification Clarification

davidtosenovjan — Mon, 15 Jan 2018 10:30:06 GMT

Yes, even after calibration you can expect some inaccuracy according to datasheet specification, of course.

Actually, I haven’t found any recommendation or requirement for SDADC re-calibration interval. AN2989, that is dealing with eQADC indeed, speaks about 100ms interval. From this point of view several seconds for SDADC seems feasible to me.

Unfortunately we don’t have specification regarding temperature drift for public.

topic MPC5777 SDADC Electrical Accuracy Specification Clarification in MPC5xxx

MPC5777 SDADC Electrical Accuracy Specification Clarification

Re: MPC5777 SDADC Electrical Accuracy Specification Clarification