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BQ27421-G1: Problem with golden image

Danilo A.
Mastermind 28590 points
Part Number: BQ27421-G1
Other Parts Discussed in Thread: BQSTUDIO, BQ27441-G1

Hi Team,

We would like to ask your help regarding the customer's inquiry below.

We are using the BQ27421 fuel gauge in our battery powered product with a 3.7V, 720mAh Li-po battery.
The default SOC percentage value given by the TI BqStudio, connected to the fuel gauge on the product or on the EVM, is wrong: at about 3.4V, it reports 5%, which is in fact about 30% according to the battery datasheet.

I have run several Learning Cycles using the BQ27421 EVM, as well as flashed the Parameter Q&A, then I extracted the Golden Image.

However when I flash the golden image on the fuel gauge, the information reported in the Registers view are still wrong, and the percentage SOC is still wrong as well.

Could you please help me figure out if I am doing something wrong in the process? Please find attached the golden image. I didn't know which parameter to choose when exporting it so I exported all 4 options with a screenshot that explains which one it is.

Golden_Images.zip

Regards,

Danilo

  • 0
    TI__Guru 61006 points

    The built-in chemistry models DOD of >0.97 for OCV > 3400mV (both versions of the gauge, G1A and G1B). The gauge isn't compatible with this cell's chemistry. There is nothing inherently wrong with your process, it's about cell compatibility. 

  • 0 in reply to Dominik Hartl11
    Prodigy 170 points

    Hello,

    What are these DOD and OCV parameters? Are you sure that the fuel gauge is not compatible with my battery? This is too late in the process for us to change the fuel gauge or the battery, as we are about to enter mass production. We have to make it work with this.

    Please find attached the battery datasheet, it's a very standard battery so I would find it really surprising that it would not be compatible with this gauge. Could you please have a look and let me know?

    Thanks

    Tracker DataSheet-LP902040NTC-900SH1.0-3Pryb.pdfTRACKER LN902040-700mah成品规格书(1).pdf

  • 0 in reply to Co Ve
    TI__Guru 61006 points

    DOD (Depth Of Discharge) is an internal variable (not a parameter) which tells the gauge how deeply the cell is discharged. The gauge calculates this by taking a relaxed voltage measurement and then it looks up DOD with the open circuit voltage (OCV) tables. These tables show a depth of discharge of 0.97 (=97% discharged) for 3400mV (important: this is open circuit, not loaded) which means that if your cell manufacturer specifies that and OCV of 3400mV equals 30% SOC (so around DOD of 0.7 (70%)) then the chemistry isn't compatible.

    This gauge isn't made to support all chemistries and unfortunately it looks to be incompatible with your cell's chemistry, based on the specification from the cell manufacturer that an OCV of 3400mV == 30% SOC.

  • 0 in reply to Dominik Hartl11
    Prodigy 170 points

    Hello

    That means we need to find a solution ASAP.

    Would the BQ27441-G1 be compatible? It has the same i2c registers so I wouldn't have to rewrite the entire firmware.

    Thank you

  • 0 in reply to Co Ve
    Prodigy 170 points

    Following up on this I have 2 questions:

    1. Can I change this OCV table to match my battery datasheet? I would change the depth of discharge of 0.97 from 3400mV to 3050mV

    2. Can I somehow trick the gauge into using my battery's parameter? For example if I add a large offset when calibrating it?

    Thank you

  • 0 in reply to Co Ve
    TI__Guru 61006 points

    We'll have to take this off E2E. I'll contact you via your provided e-mail address.