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BQ27520-G4: VOK bit not set while doing the learning cycle

Jeremy HU
Prodigy 20 points
Part Number: BQ27520-G4
Other Parts Discussed in Thread: BQ27520EVM, , BQSTUDIO, BQEVSW

Hello,
I am doing the battery learning cycle for bq27520-G4 using the bq27520EVM, but have some trouble.

First of all, I never see VOK bit been set, though I can see the QEN and RUP_DIS bits got set.
Without VOK been set, I can not finish the learning cycle.
The "Update Status" of Data Memory is always 0.

I tried the following software:

  • Battery Management Studio ( bqStudio ) 1.3.54
  • bq Evaluation Software ( bqEVSW ) Version 0.9.92

No one works for the VOK bit, no matter how I follows the wizard of bqEASY or send the IT_ENABLE command manually.

And there is another problem,
When I parse and execute the commands of the 0520_3_29-bq27520G4.df.fs in the host cpu, it always failed on this line:

C: 16 04 D6 D4 91 4C

The value read is "04 00 00 00", not equal to "D6 D4 91 4C".
Finally, I choose to parse the gg.csv file and convert to i2c commands and update the data flash in firmware mode(Not ROM mode).

In conclusion, can anyone help me to answer these two questions please:

  1. How can I get the VOK bit been set?
  2. Without learning cycle, is it ok to go production just update the data flash with unlearning parameters(I known the Chemical ID is right, and I tested with our real product device, the percentage of battery is good).

Thanks in advance.

  • 0
    TI__Guru* 76230 points

    How can I get the VOK bit been set?

    It appears you your cells never get to be fully relaxed. Pls carry out learning as per this attached ppt.

    .2577.LearningCycleOverview_.pdf

    Without learning cycle, is it ok to go production just update the data flash with unlearning parameters(I known the Chemical ID is right, and I tested with our real product device, the percentage of battery is good).

    OA: i wouldn't recommend that, but if you have to do that, make sure your qmax in data flash is changed to a value close to the nominal capacity of your battery, and change update status to 02. This will allow the gauge maintain that accuracy you see over the lifetime of the battery.

    thanks

    Onyx

  • 0 in reply to Onyx Ahiakwo
    Prodigy 20 points

    Hi, Onyx

    Thank you very much for the reply.

    How can the cell be fully relaxed? What ever I discharge to empty and leave it there for more than one day,  or charge to full and leave it there for more than one day, I never saw the VOK bit been set.

    According to the document, first I need see VOK been set, then after full discharge/charge and relax, I need see VOK been clear. 

    From sluu426b, Figure 6, for my understanding, the "Power Supply 3.6V" is our battery, right? Do we need another power supply for the evm board? Because we just use the battery to supply power. Is this cause the battery not relax? If we need another power supply, Which pin should connect on the evm board?

    I have attached my df.fs and gg.csv files as battery.zip.

    I observed the Qmax value in the "Gas Gauging" is right(The same as I configed on the bqEASY), but the Qmax value in the "OCV Tables" is wrong.

    "Gas Gauging","State","Qmax Cell 0","4800","mAh"

    "OCV Tables","OCVa0 Table","Qmax Cell","1000","mAh"

    Should I change it manually to the same please?

    battery.zip