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FD_aurix
Level 5
Level 5
100 sign-ins 100 replies posted 5 solutions authored

Hi all

I've activate startup calibration and I was looking if it was mandatory to do also the post-conversion calibration and what are the effects to skip it

from the manual we have only this note

"Postcalibration steps can be appended to each conversion. Since variation caused by aging is very slow and
postcalibration leaves the capacitor discharged, for the current version of the converter postcalibration shall be
disabled (most applications are restarted periodically and, therefore, also repeat the start-up calibration)."

but I can't find any data related to "very slow".

Can I skip the post calibration if my application could work for 24hr continuosly? and if could work for 1month/yr continuosly? 

Is variation caused by aging only the only cause that require a postcalibration?  

 

later in manual we have

"In systems with a stable reference voltage, it is recommended to disable postcalibration permanently to avoid
these effects by setting bit DPCAL in register GxANCFG (x=0-11).
In systems where the reference voltage is influenced by temperature, postcalibration can be enabled temporarily
during certain operation phases to compensate these effects."

so it seems that at least post calibration is needed if the reference voltage is not stable.

 

Other conditions need to be taken in account?

 

 

 

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Meet_T
Moderator
Moderator
Moderator
25 likes received 50 solutions authored 100 replies posted

Hi @FD_aurix , Yes as mentioned in the UM generally the post calibration could be disabled, but we need to check internally if it has to be executed if the ECU is running continuously for 24 hrs / 1 month / 1 year.

 

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Meet_T
Moderator
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25 likes received 50 solutions authored 100 replies posted

Hi , Could you please let us know what is the application for this?

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FD_aurix
Level 5
Level 5
100 sign-ins 100 replies posted 5 solutions authored

Hi Meet 

I don't understand why it is important to know my application.  I need to have some generic indication on how to proceed with post calibration and then we will see how to perform it in our different cases.

BTW I've different possible application that has different used cases. In some applications the customer is forced to switch off/on the device periodically (to recharge the battery) so we can consider maximum 24h of working time but other application are 24/24 7/7  connected to an UPS so in the worst case they are not switched off for years!

For this reason I was looking to some general rule and I might force a re-calibration in some particular condition

 

In any case I've done some test and I've noticed relevant glitches on the converted output if post calibration is active that after each end of conversion are not present at all as soon as it is de-activated. Is something already known? we need to check the capacitance related to the single analog input? there is some design rule to prevent this behaviour?

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Meet_T
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Moderator
Moderator
25 likes received 50 solutions authored 100 replies posted

Hi @FD_aurix , 

For above query regarding long time running EVADC application e.g. one year, our feedback is:

1. do not use post calibration in any case, as it is already written in user manual
2. in case of reference voltage change, or huge temperature change (e.g. from cold to hot), user needs to repeat the start-up calibration one time
3. if time allows, user can manually trigger the start-up calibration e.g. a few times per day, to be make sure on the safe side

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FD_aurix
Level 5
Level 5
100 sign-ins 100 replies posted 5 solutions authored

Hi Meet_T

Please be precise. It is important. 

In manual it is recommended to disable it permanently in application with stable voltage referee ->activate it in case of variation of voltage reference.

From your reply it seems we are never allowed to activate post calibration but we need to re-calibrate the ADC with the startup sequence.

Please define few time per day and "from cold to hot". 

 

Sorry to be fussy but I feel that this information is quite relevant since it involve ADCs that often are related so important signals for the control and for the safety.

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