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BQ27621-G1: BQ27621-G1 : Issue in reading accuracy

alpesh mandani
Intellectual 690 points
Part Number: BQ27621-G1
Other Parts Discussed in Thread: BQ25100, BQ27426,

Hello,

We're currently using a BQ27621-G1 gas gauge for a  low-power application with bq25100 Battery charger IC. The battery is 100mAh and normal operation mode average currents are ~12mA and sleep mode current is ~0.6mA. The gas gauge is configured for the low capacity according to technical reference manuals.

We have read following value using Standard Commands configuration:

  • Voltage = 4184
  • NominalAvailableCapacity = 146
  • FullAvailableCapacity = 148
  • RemainingCapacity = 146
  • FullChargeCapacity = 148
  • EffectiveCurrent = 00
  • StateOfCharge = 99
  • RemainingCapacityUnfiltered = 146
  • RemainingCapacityFiltered = 146
  • FullChargeCapacityUnfiltere = 148
  • FullChargeCapacityFiltered = 148
  • StateOfChargeUnfiltered = 99


We have the following question

  1. We observed state charge is 99% and normal availability capacity is 146mHA in above reading and it is hight then our battery capacity of 100mAH. Can you please help me to resolve this issue?How to get accurate values as per battery capacity?  Is it correct behavior?
  2. When I plug the charger into the board, BQ27621 shows battery level 100% and unplug charger, then I have placed unit in discharging state and got battery SOC value 50% after 8-9hours ,then the battery values are starting to go down around 53%  after that after minute-two show battery capacity is 0% and system goes to shut down mode. What can problem in SOC reading or configuration of fuel guage? Can you please help me to resolve this issue?

Looking forward to hearing from you.

  • 0
    TI__Guru* 76230 points
    Hi Alpesh,
    Have you reviewed the quick start guide of your device ?
    www.ti.com/.../sluuap5a.pdf

    I fear the capacity of your cell is really small than the gauge can handle and you might have to employ the scaling approach described in the app note below:
    www.ti.com/.../slua792
    thanks
    Onyx
  • 0 in reply to Onyx Ahiakwo
    Intellectual 690 points

    Hi Onyx,

    Yes, We have reviewed Quick start guide and updated following parameter as mentioned in the guide.

    1. Toggle Power Min = Enable
    2. Design Capacity = 100mA
    3. Design Energy= 370mW
    4. Terminate Voltage =2.8V
    5. Taper Rate= default

    Let me know any other parameter we need to configure.

    You have shared scaling approach app note for Shunt based monitoring IC bq27426 but we have used voltage based monitoring IC BQ27621-G1. So Please correct me if I am wrong.

    Thanks.

    Regards,

    Alpesh Mandani

  • 0 in reply to alpesh mandani
    TI__Guru* 76230 points
    Hi Alpesh,
    Try scaling the design capacity and energy and see if tht helps
    thank
    Onyx
  • 0 in reply to Onyx Ahiakwo
    Intellectual 690 points

    Hi Onyx,

    Thanks for your suggestions.

    Let me process of scaling and which register we need to configure.

    Because we also facing issues on SOC reading and we need to configure SOC value value 0% at 3.0Volt and 100% at 4.2Volt. which register will help to us?

    Thanks.

    Regards,

    Alpesh

  • 0 in reply to alpesh mandani
    TI__Guru* 76230 points
    Hi Alpesh,
    Pls review the primary charge termination section of the technical reference manual. It contains important info that address your questions

    For the gauge to behave as you so desire, you need to set the v at chg term to what your charging voltage is.
    Then you need to set your terminate voltage for when the gauge reports 0. You need to set the parameters described in the quick start guide of the device correctly, i.e taper rater, design capacity etc.

    thanks
    Onyx