Other Parts Discussed in Thread: BQSTUDIO, BQ27426, BQ27510
Hello,
We have designed a device which uses a bq27421-G1A. The Fuel Gauge is connected, through a protection circuit, to the battery.
We configured the fuel gauge with the correct parameters for Battery Capacity, Battery Energy, Termination Voltage and Taper Rate and performed a Learning Cycle using bqStudio to obtain the Ra Tables to attempt to improve the accuracy of the fuel gauge.
Unfortunately, we are still experiencing problems with SoC estimation. We submitted log files to identify the Chem ID for the cell. We obtained the following report:
Summary of all IDs with max. DOD deviation below 3%
Chem ID max DOD error, % Max R deviation, ratio
3171 2.86 0.1
1242 2.91 0.23
Max. deviations for best ID is within recommended range. Chosen best chemical ID is suitable for programming the gauge.
Selection of best generic ID for ROM based devices like bq274xx
Device / Family #1
Generic Chem ID Device/ Voltage/ Chemistry max DOD error, %
3142 bq27421-G1D: 4.4V LiCoO2 9.67
354 bq27411-G1C: 4.35V LiCoO2 11.92
128 bq27421-G1A: 4.2V LiCoO2 16.24
312 bq27421-G1B: 4.3V LiCoO2 19.07
Best generic ID 3142
Warning: Deviation for best generic ID is above recommended level for this device / family. Consider using another device, flash based gauge or RAM programming of custom ID.
Device / Family #2
Generic Chem ID Device/ Voltage/ Chemistry max DOD error, %
1202 bq27621: (default) 4.2V LiCoO2 11.15
1210 bq27621: (ALT_CHEM1) 4.3V LiCoO2 11.31
354 bq27621: (ALT_CHEM2) 4.35V LiCoO2 11.92
Best generic ID 1202
Warning: Deviation for best generic ID is above recommended level for this device / family. Consider using another device, flash based gauge or RAM programming of custom ID.
Device / Family #3
Generic Chem ID Device/ Voltage/ Chemistry max DOD error, %
3142 bq27426: (ALT-CHEM2) 4.4V LiCoO2 9.67
1202 bq27426: (ALT_CHEM1) 4.2V LiCoO2 11.15
3230 bq27426: (default) 4.35V LiCoO2 13.01
Best generic ID 3142
Warning: Deviation for best generic ID is above recommended level for this device / family. Consider using another device, flash based gauge or RAM programming of custom ID.
Our understanding is that we have to replace bq27421-G1A with another part if we wish to increase gauging accuracy. Is that correct? Are there any BGA programmable chemistry FG (possibly with integrated sense resistor) that you can suggest?
In our application, the system will operate at a constant temperature of 40C. Is there any advantage in performing the ChemID characterization at the same temperature?
Thanks,
Luigi Zevola
