BQ78350-R1: New Chemistry ID Generation

Hi Ansul,

Getting a new ChemID generated is a long process (cells sent to TI and there is a long queue in the battery characterization lab), so let's first look at your results from the GPCCHEM tool to see if we can help you get better results. Can you tell us the part number for your cell and send a datasheet if you have one? Can you send the file you submitted to the GPCCHEM tool and the results?

Thanks,

Matt

Hi Matt,

Data that I had used for getting matching ChemID is attached with this message. Kindly have look at it.

We have Cell Testers and thermal chambers at our facility. We can do the data collection for cell characterization if TI can share the details..

I not very confident about sharing the cell information on the Forum. I can send a mail/message regarding this. let me know if this works

CC8.zip

Hi Ansul,

Do you also have the results from the GPCCHEM tool you can share?

I'll send you a private E2E message if you can also share your cell information (part #).

Thanks,

Matt

Hi Ansul,

I also wanted to explain something unique to BQ78350. The BQ78350 uses a CEDV gauging algorithm. For CEDV gauges, ChemID is not critical to gauging accuracy. Most CEDV gauges do not require a ChemID. Impedance Track gauges need a good ChemID match because the algorithm relies on the ChemID information to recalculate the QMax for each cell after each voltage measurement during rest periods.

The BQ78350 is unique in that it does use ChemID also, but it only uses it to estimate the initial SOC after powering on the device, coming out of Shutdown, or after a RESET command. After the initial estimation, ChemID is no longer used at all. The more important thing for the BQ78350 is to correctly set the CEDV gauging coefficients. This is described in the Using the BQ78350-R1 document (see the Gas Gauging section of the document). 

So ChemID only becomes important if you frequently shut down the device. When the device shuts down, the remaining capacity register is cleared, so the device can only use cell voltages to estimate the capacity on power up. 

I also want to mention that we recommend the BQ78350-R1A. This is functionally identical to the R1 but it comes pre-loaded with the latest version of the firmware which improves the robustness of the device Shutdown routine. 

Best regards,

Matt

Hi Matt,

Yes, You are right.

The application (circuit) we are working for, needs to have a good estimate of initial SOC.

GPCCHEM report for cell data that I had previously sent is attached to this message

Chemistry ID selection tool, rev=2.5		
		
Configuration used in present fit:		
ProcessingType = 2		
NumCellSeries = 1		
ElapsedTimeColumn=0		
VoltageColumn = 1		
CurrentColumn = 2		
TemperatureColumn = 3		
		
Best chemical ID : 2079	Best chemical ID max. deviation, % : 1.03	
		
		
		
Summary of all IDs with max. DOD deviation below 3%		
		
Chem ID	max DOD error, %	Max R deviation, ratio
2079	1.03	0.25
247	1.06	2.24
1594	1.11	0.46
2405	1.13	0.58
295	1.13	0.49
2051	1.14	1.41
252	1.17	0.6
3385	1.2	3.67
231	1.24	0.45
2041	1.25	3.47
2309	1.26	1.14
264	1.29	0.42
297	1.33	0.68
1352	1.38	0.76
1331	1.44	0.65
2682	1.44	0.57
1351	1.45	1.43
2077	1.46	1.51
1280	1.46	1.09
1268	1.48	1.07
1282	1.49	0.71
2023	1.51	0.79
2091	1.52	1.35
2102	1.57	1.19
2082	1.58	0.46
1996	1.59	1.8
2084	1.6	0.76
2802	1.62	0.38
1991	1.64	0.55
2286	1.64	0.4
218	1.65	0.58
2776	1.65	0.38
275	1.66	2.35
2188	1.68	0.62
1300	1.68	2.28
1653	1.71	0.65
1267	1.71	0.33
208	1.71	0.73
203	1.71	0.73
200	1.71	0.73
1647	1.73	0.67
206	1.74	0.74
2148	1.75	0.42
2066	1.77	0.51
221	1.77	0.87
1301	1.79	0.61
239	1.79	0.45
2590	1.84	0.57
1325	1.84	0.53
1340	1.88	0.81
234	1.91	0.87
2053	1.95	0.96
253	2.08	0.26
260	2.09	2.33
2645	2.1	0.46
1332	2.22	1
1323	2.27	0.62
2487	2.27	0.36
2568	2.3	0.37
2605	2.46	0.27
1741	2.51	0.54
291	2.52	0.46
201	2.54	1.18
1314	2.59	0.94
1253	2.69	0.63
2833	2.72	0.38
1284	2.74	0.75
1281	2.74	0.75
2126	2.74	0.99
2407	2.76	1.2
2554	2.76	0.41
242	2.82	0.44
2094	2.85	0.54
2106	2.87	0.54
2127	2.88	0.36
2636	2.91	0.59
263	2.92	0.61
2877	2.96	0.65
2078	2.96	0.71
286	2.96	0.59
2151	2.97	0.36
3596	2.97	1.06
2065	2.98	1.04
4129	2.98	0.64
		
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, %
354	bq27411-G1C: 4.35V LiCoO2	13.21
3142	bq27421-G1D: 4.4V LiCoO2	13.6
128	bq27421-G1A: 4.2V LiCoO2	29.45
312	bq27421-G1B: 4.3V LiCoO2	35.59
Best generic ID 354		
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, %
354	bq27621:  (ALT_CHEM2) 4.35V LiCoO2	13.21
1210	bq27621:  (ALT_CHEM1) 4.3V LiCoO2	16.96
1202	bq27621: (default) 4.2V LiCoO2	18.47
Best generic ID 354		
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, %
3230	bq27426: (default) 4.35V LiCoO2	12.44
3142	bq27426: (ALT-CHEM2) 4.4V LiCoO2	13.6
1202	bq27426: (ALT_CHEM1) 4.2V LiCoO2	18.47
Best generic ID 3230		
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.		
		
		

Hi Ansul,

From the GPCCHEM report, it looks like you got very good results with several very close matches. You are not going to be able to improve your results by sending a cell for characterization.

Remember, for the BQ78350, ChemID is only used to determine SOC based on voltage. So if you choose one of the ChemIDs recommended by the report, you will have a very closely matched OCV curve.

One other thing to keep in mind if you are planning to frequently use the Shutdown feature - Battery cell voltages take up to 2 hours to fully relax after active charging and discharging, so the cell voltage may not accurately predict SOC if the cells are not fully relaxed.

Best regards,

Matt

Hi Matt,

I got your point. But my concern is Cell capacity.

Cell that I used for data collection has nominal capacity of 2500mAh

GPCCHEM report suggested best match id as 2079, whose capacity is 4250mAh.

How is this difference considered while estimating initial SOC and Remaining Capacity (RC).

Hi Ansul,

The important thing is that the voltage curve matches. You will input your battery's capacity in the Design Capacity parameter.

Best regards,

Matt