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BQ27520-G4: Incorrect SOC & SOH Readings

Stephanie Hiszpanski
Prodigy 20 points
Part Number: BQ27520-G4
Hello, 
I was able to successfully generate a Chem ID and updated Ra tables for our BQ27520 using this TI app note.  Unfortunately we have noticed a few discrepancies in our readings - 
1. State of Charge: 
With a fully discharged battery this value jumps from 0 to 100 in ~2minutes after charging begins. Same with fully charged and discharging (100 to 0 in ~2mins). This does not seem right?
2. State of Health: 
This value never changes from 48% when testing on a new cell. This seems low? How often should this update?
Below are the Chem ID results and I have attached the .gg file with our Ra values. Can you please let me know if anything looks incorrect for our 2000mAhr 4.2V Lithium-ion Polymer (LIP) cell?

Best chemical ID : 256 Best chemical ID max. deviation, % : 2.88

Summary of all IDs with max. DOD deviation below 3%

Chem ID max DOD error, % Max R deviation, ratio

256 2.88 0.59
  • 0
    TI__Guru 57747 points

    Hello Stephanie,

    Can you elaborate on whether you had a successful learning cycle for Ra Table updates?

    The bq27520 has slightly different parameters and this is the correct reference for it.

  • 0 in reply to Shirish
    Prodigy 20 points

    Hello, 

    Yes, I believe it had a successful learning cycle as the values in Ra0 Table updated (though this took me about 5-6 cycles before I was able to get it to update). I then copied those values to all other Raxx fields as shown in the .gg file I attached.  

    Ra0 Default
    Ra1 Default
    Ra0 Table  <-- This is the only one that updated during the learning cycle
    Ra1 Table
    Ra0x Table
    Ra1x Table

    I was using the application note you referenced but someone else on this forum told me to use slua777 instead. 

  • 0 in reply to Stephanie Hiszpanski
    TI__Guru 57747 points

    Hello Stephanie,

    It is ok to use other documents for reference as there is more detail there. The goal is to have successful learning. I don't see Update status reflecting the learning, that is why i asked.

    Also a new cell must show 100% SOH as it is the one used for learning.

  • 0 in reply to Shirish
    Prodigy 20 points

    Thank you. It sounds like the Ra Tables did not update correctly then if the Update Status does not reflect this. I will try to do the charge/discharge cycles again. When the Ra Table updates correctly, will the Update Status of the BQ27520 change to 02 and then persist?

  • 0 in reply to Stephanie Hiszpanski
    TI__Guru 57747 points

    Hello Stephanie,

    Yes, once update status changes to 02, read out the image(similar process to reading golden image) so that you have a good reference point for comparison.