System Level Calibration.

Question

Hi, I am interesting system level calibration of AD5522. (I mean self calibration or calibration without any additional instruments.) 
 
 I read the below thread but still don't clearly understand how we handle system level calibration after power-on. 
 MI calibration method of AD5522 
 
 So, At the AD5522 datasheet page 39 i assume that we not need any additional DUT or board or instrument for system level calibration. 
 FV mode for instance datasheet explain 2 point calibration. 
 Connect SYS_FORCE to FOHx and SYS_SENSE to MEASVHx. and load FIN dac 0x0000 and 0xFFFF then activate internal 10K resistor by closing SW7 switch. And using system PMU measure errors. 
 
 First of all SYS_FORCE and FOHx is can connected each other. if I can turn on 60 OHM switch. (Same as SYS_SENSE to MEASHVx.)

Secondly what is that mean "Using the system PMU, measure the error between the voltage at FOHx/MEASVHx and the desired value". Normally we should tight up FOHx and MEASVHx pins together. 
 I can't clearly understand the procedure. Can someone explain me how we can execute system level calibration? 
 
 Thanks 
 Oki

MacManato · Accepted Answer

Hi, oki.developer. 
 You are right with the statement FOHx and MEASVHx are tied together, may it be internally or through external means. I think the confusion lies on the word "FOHx/MEASVHx". They are basically the same node and it is expected that you are going to measure the same potential whichever of the two you choose, thus the "/" or "or" differentiator. You only have to pick what you want to measure among the two pins (SYS_FORCE or SYS_SENSE) and compare it with the desired value (which pertains to the voltage you were trying to force initially, e.g. if you put on the hex code for 5V, you use 5V as your desired value). The datasheet provides means for the customers to be able to do the calibration but doesn't intend to instruct the customers what calibration scheme to use - just accurate measurement from these key nodes. The system PMU is an external measuring unit used by customers in their system to accurately measure voltages (may it be from the SYS_FORCE and SYS_SENSE pins or practically anywhere else). 
 Best regards, Mac)

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