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BQ20Z75 issues

Viktorija Cecil
Mastermind 18501 points

Team, my customer is asking:

We are currently using the BQ20Z75 IC for a 2S1P Lithium Ion battery pack design.  We are seeing the following issues:

 

1)      When the Absolute state of charge (Reg: 0x0e) percentage reaches above 90% we see the charge state jump from 92-89%, 90-93%, 96-99%, 99-96% randomly. Although the Remaining Charge Capacity(Reg: 0x0f)  reports the proper Status .

The current charger is not an SMBus gas gauge charger, if that makes a difference.

2)      At the same time when we unplug the unit we can see the charge percentage go from 90% up to 95%.  This happens when #1 listed above happens and then we just simply remove the charger from the battery pack

3)      We have included the log files from our Gas Gauge Evaluation that show the issue that we see.  You will see that the State of Charge shows 99%, and then goes directly to 96% and then goes back to 99% within a short period of time.

 

What we want to understand is if this is a typical function of the battery pack to jump around during charge as indicated above.  And also why this is happening.

 

We want to understand what is going on with this, and this is causing an issue with our customers production of the battery packs as we don’t know exactly what is causing this issue.  Please let us know if you have any information on this that you can share.  If you are not able to provide documentation on this concern, please let us know what can be done to get an Engineer on site so we can review this issue.

 

I have also included photos of two different IC’s, one from 2014 and one from 2106 for your reference.

 

Please let me know at your earliest convenience when we can set something up.  This is an urgent matter.

Thanks

Viktorija

Pictures below. 

Log files wouldn't attach. I can send them via email. 

  • 0
    TI__Expert 6575 points

    Hi Viktorija,

    I looked at the log files, but it is hard to see what the time scale is.

    One question, are the log files in sequence i.e. 92%->89%->90%->93%->97%->94%->96%->99%->96%?

    Also in the 99%->96% case I noticed that there is a strange value for RemCap = 2560:

     

    Is it possible that this is due to some bit shift during communication?

    There is no smoothing on these older devices, so RSOC = RemCap/Fcc, so it dosent make sense that RSOC will jump like this if RemCap and Fcc are pretty consistent.

     

    Regards,

     

    Swami