Hi Mike,
as indicated in the AN12301.. NXP performs a calibration of each device and stores corresponding data inside the device ROM memory. Soldering the device onto a PCB induces stress (mainly mechanical) on the silicon die which is changing electrical properties. For your use-case using the VSENSE_EXT (PTBx pins) the main parameter will be the voltage reference (Vref) used to scale the ADC results:
e.g. adc_value = Vin * 1/ Vref * 65535
The VSENSE3..VSENSE0 would have additional influenced internal resistor divider influence.
NXP has not collected extensive data how strong the influence of the soldering is and we also do not know how customers solder the devices in different applications / manufacturing lines.
The things I can comment:
- for the VSENSE_EXT the impacted should be quite the same for each channel (I have one customer who only system calibrates one channel and applies the same delta to the other channels, which was also verified using data collected by that customer). You could evaluate if you could do the same!
- not knowing your accuracy requirements: you could check with a significant statistical number of devices how strong the accuracy is impacted by the soldering and estimate if you can fulfill you specification (this has to be performed by you, on your PCB, under your mass production manufacturing conditions, etc.) without a system calibration
- you should have an accuracy validation in your manufacturing. I recommend to use that step and with little additional effort (time) you can rather system calibrate each sensor than just checking it.
Let us know if you have additional questions? We can also schedule a conference call if that is more efficient!
Rgds
Wolfgang
