Other Parts Discussed in Thread: GPCCHEM, BQ27Z561
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Hi Andy,
Thank you for the reply. I am attaching the report with this mail please have a look
Chemistry ID selection tool, rev=2.49 Configuration used in present fit: ProcessingType = 2 NumCellSeries = 1 ElapsedTimeColumn=3 VoltageColumn = 7 CurrentColumn = 13 TemperatureColumn = 6 Best chemical ID : 2150 Best chemical ID max. deviation, % : 2.06 Summary of all IDs with max. DOD deviation below 3% Chem ID max DOD error, % Max R deviation, ratio 2150 2.06 0.24 2152 2.19 0.41 1762 2.24 0.38 224 2.31 0.68 2155 2.31 0.44 2380 2.32 0.46 2348 2.38 0.35 1895 2.4 0.39 2104 2.47 0.38 2021 2.49 0.85 2445 2.58 0.55 2419 2.59 0.53 2002 2.61 0.73 2404 2.62 0.37 241 2.63 0.85 2588 2.74 0.56 2408 2.75 0.62 2317 2.76 0.53 2187 2.82 0.78 2429 2.94 0.41 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 15.76 354 bq27411-G1C: 4.35V LiCoO2 16.01 128 bq27421-G1A: 4.2V LiCoO2 28.12 312 bq27421-G1B: 4.3V LiCoO2 29.73 Best generic ID 3142 Warning: Generic ID Deviation is so high that it is most likely due to anomaly in the data. Please check that data files have recomended format, units and test schedule Device / Family #2 Generic Chem ID Device/ Voltage/ Chemistry max DOD error, % 1210 bq27621: (ALT_CHEM1) 4.3V LiCoO2 15.85 354 bq27621: (ALT_CHEM2) 4.35V LiCoO2 16.01 1202 bq27621: (default) 4.2V LiCoO2 17.94 Best generic ID 1210 Warning: Generic ID Deviation is so high that it is most likely due to anomaly in the data. Please check that data files have recomended format, units and test schedule Device / Family #3 Generic Chem ID Device/ Voltage/ Chemistry max DOD error, % 3142 bq27426: (ALT-CHEM2) 4.4V LiCoO2 15.76 3230 bq27426: (default) 4.35V LiCoO2 16.7 1202 bq27426: (ALT_CHEM1) 4.2V LiCoO2 17.94 Best generic ID 3142 Warning: Generic ID Deviation is so high that it is most likely due to anomaly in the data. Please check that data files have recomended format, units and test schedule Warning: Max R deviation ratio can not be checked because discharge hr-rate is above 12. Hr rate = 22.9759911961134 Warning: Max R deviation ratio can not be checked because discharge hr-rate is above 12. Hr rate = 22.9759911961134 Warning: Max R deviation ratio can not be checked because discharge hr-rate is above 12. Hr rate = 22.9759911961134
By the datasheet, the total capacity of the battery is 4400 mAh, 16280 mWh and the cut off voltage is 2.7V and we are setting the same for the configuration of BQ27441, but for our design, we can't go up to 2.7V, we are stoping the discharge when the voltage reaches only 3.4V thereby we are not using the total 4400mAh or 16280 mWh. Will it be the cause for the issue?
Hello Sajin,
You will need to look at the Qpass register during the discharge. If it is not even 90% of the discharge vs. design capacity, I would recommend setting the terminate voltage to 3.4 volts if that's your system shutdown voltage.
Hi Kang,
We will test that thing that you have said about the Qpass register and update it with you.
I have one more doubt is there, It is about the CC_GAIN. We had a current measurement accuracy issue previously and it was solved by altering the value in CC_GAIN register. But by going through the datasheet I got to know that CC_GAIN is no for customer usage and it is only for debugging purposes, so is that mean we can't alter the CC_GAIN value? Is it not the proper way to tackle the error in current sensing? If so what is the proper method?
You can change CC_GAIN. It is not restricted to debugging only.
About gauge accuracy: The gauge uses the built in ChemID to run discharge simulations. You must complete a successful learning cycle where the gauge can measure QMax and cell impedance. This requires accurate current measurements.
A learning cycle is basically a series of controlled charge/relax/discharge/relax sequences. See https://training.ti.com/how-perform-successful-learning-cycle-gauges
Once the gauge learned these properties, it will be as accurate as the built-in ChemID allows for the cell that you use.
Make sure that you configure charge termination correctly (you use C/27.5 but a C/25 with a taper rate of 250 is more appropriate for your taper current - the guideline is 15% more current than your taper current to make sure that the gauge detects charge termination reliably).
Also verify that the discharge/charge and quit current thresholds are compatible with your application. The gauge must be in the correct state (charge/discharge/relax) for this to work.