What are the ramifications to calibration and gas gauge accuracy when using a bq27541 and op amp buffer. Impedance track algorithm specifies a 1mV accuracy in voltage measurements..Issues/Questions:
1) 0.1% resistors would be 8.4mV worst case error, plus op amp input offset errors of 3mV would lead to 11mV difference between true 0.5*Vbat and actual amp output. Is Impedance track somehow able to adjust voltage errors, or is the algorithm insensitive to absolute offsets.
2) going into production with bq27541, for calibration SLUA504 mentions using averaged calibration factors for voltage, coulomb counter, etc. Is this applicable when using the op amp?
3) Are there any issues with the chemistry selection when using the op amp ckt. Should the Matchcad characterization be used if an op amp is used, even though the chemistry is defined. It seems to me this might be a good way to get around the voltage offsets, but it depends on ho the Ra, and chemistry info are used in the IT algorithm
1) you have to calibrate the voltage to get the offset.
2) yes, if your average data has small sigma. if components variation and board to board variation is too big, the averagae approach can not be used regardless it is once cell or two cell.
3)no, chemistry ID selection is not cell dependent. It is chemistry dependent. However, learning cycle results are cell configuration dependent.