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Choosing a ROM gauge to match Lithium Battery Chemistry

Adam Johnson
Expert 1310 points
Other Parts Discussed in Thread: GPCCHEM, BQ27426, EV2400

I am developing a product with a 3350 mAh Panasonic NCR18650B Lithium-ion battery (Chem ID 2012), and am trying to pair that with a gas gauge.  I'd really like to avoid having a production fixture which must load a golden file to the gauge, so I'm interested in a ROM gauge like the BQ27441.  However, the BQ27441 has the Chem ID fixed at 0128.

How accurate can I expect a ROM gauge to be compared to a Flash gauge with the correct Chem ID selected?  Is the BQ27441 a good choice for me?

Thank you,

Adam J.

  • 0
    TI__Guru* 76230 points
    Hi Adam,
    The expected accuracy with our ROM gauges is 5% or better if the cell is a match with the defaults in device. If it isn't the accuracy can off by as much as 20%. I recommend you use the gpcchem tool to see how close a match your cell is to the chem id programmed on the device.
    Our latest ROM gauge is the bq27426, I recommmend using that one over the bq27441.

    with regards to your comment on using a production fixture, you can program your devices using your host controller the same way you will have to do the settings on the bq27441 or the bq27426 in order for it to work with your battery.


    thanks
    Onyx
  • 0 in reply to Onyx Ahiakwo
    Expert 1310 points

    Fullscreen 6472.GPC_report.txt Download 
    Chemistry ID selection tool, rev=2.13		
		
Configuration used in present fit:		
ProcessingType=2		
NumCellSeries=1		
ElapsedTimeColumn=0		
VoltageColumn=2		
CurrentColumn=3		
TemperatureColumn=1		
		
Best chemical ID : 2076	Best chemical ID max. deviation, % : 1.27	
		
		
		
Summary of all IDs with max. DOD deviation below 3%		
		
Chem ID	max DOD error, %	Max R deviation, ratio
2076	1.27	0.19
238	1.3	0.27
2034	1.34	0.16
285	1.34	0.17
2036	1.34	0.16
281	1.44	0.15
288	1.53	0.27
278	1.57	0.36
2019	1.62	0.34
2052	1.64	0.27
2017	1.65	0.23
2042	1.86	0.19
232	1.87	0.35
2056	1.9	0.3
2012	1.96	0.2
284	2.01	0.31
2020	2.2	0.39
246	2.27	0.42
3166	2.3	0.36
2037	2.33	0.24
1273	2.52	0.59
2040	2.55	0.39
2043	2.6	0.32
2097	2.6	0.32
299	2.65	0.31
2004	2.87	0.33
2061	2.9	0.29
2064	2.96	0.27
		
Max. deviations for best ID is within recomended range. Chosen best chemical ID is suitable for programming the gauge.

    I've used the gpcchem tool to upload data from a rel-dis-rel test and determine my Chem ID.  I've attached the results above.  The bq27426 supports Chem IDs 3230, 1202, and 3142, none of which are recommended by the gpcchem tool.  But do you even have a ROM-based gauge that supports any of the recommended profiles?

    Wait...what is the point of creating a golden file if I can program the flash-based gauges in the same way as the ROM-based gauges?  Is there just so much stuff to program that for many people it's easier to always use TI software and an EV2400 to program, rather than put all that in their host controller's firmware?

  • 0 in reply to Adam Johnson
    TI__Guru* 76230 points

    Hi Adam,

    I looked at the report and the criteria for determining a match for the rom gauges is not listed on there. The criteria is 5% in ROM gauges and our old matcad tool had provisions for that. Do you have a matcad  license to use the old mathcad tool? if you do not, attach you log files and i will help you run it. Those profiles that are listed for those ROM guages in the data sheet are the only ones available. We do not make ROM gauges for each and every profile. If you would need a more robust gauge that enables the programming of any profile, you should use the flash based gauges.

    the golden file is in an srec , dffs or bqfs format for flash based gauges. You can parse the data in the flashstream format on the guage using your host controller. We have an app note that describes this process. See attached.

    6087.slua541.pdf

    thanks

    Onyx

  • 0 in reply to Onyx Ahiakwo
    Expert 1310 points

    2678.config.zip

    Onyx,

    Attached please find the zip file I uploaded to the  gpcchem tool to obtain the GPC report shared above.  I don't have MathCad; could you run this for me?

    Thank you,

    Adam J.

  • 0 in reply to Adam Johnson
    TI__Guru* 76230 points
    Hi Adam,
    I ran the file through the tool and unfortunately none of the chem ids on our rom based gauges is a match for your cells. You will have to use a flash based gauge .

    thanks
    Onyx