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Original question:

BQ27441EVM-G1A: Evaluation Board

BQ27441EVM-G1A: Evaluation Board

Pushpendra Singh
Prodigy 70 points
Part Number: BQ27441EVM-G1A
Other Parts Discussed in Thread: BQ25798EVM, BQ25798

Tool/software:

Hello!

I had some questions that came up when we were testing the development boards of BQ25798 and BQ27441. I have currently run a lot of charging and discharging cycle tests with our 7.8Ah battery pack. The next thing I was working on was trying to run a simulated solar panel charging cycle for the battery pack with the help of BQ25798EVM and BQ27441EVM. 150mA of constant current and 120mA of ITerm. Since it will take a lot of time to charge the battery pack, we figured we would leave the battery pack charging and the log the gas gauge readings with the help of BQ27441EVM and BQ Studio. Here is what the log picked up :

As you can see in this, the charger was charging the battery pack with 148mA of constant current for upto 16% of the battery pack capacity and then there was a sudden drop in the average current. I am not sure what caused this, and I am trying to figure that out. The data in the logs after the charging stopped are pretty much the same as the data in the charging time. The only thing that is changing is the CTRL STATUS from 0x0088 to 0x0098 but that too is hopping between the two values as I have highlighted in the data.
Can someone from your team explain to me why this would have happened? What exactly does the switching between 0x0088 and 0x0098 is something I notice in the CTRL STATUS register? It was constantly at 0x0088 when it was charging from 0 to 16%. What does 0x0088 and 0x0098 tell us here? Does the log tell us anything about what might have caused the charger to stop delivering current to the battery pack and hence gas gauge stopped reading any average current data? 
Here is a picture of the setup : 
I would really appreciate some help. Thank you!
  • 0
    Prodigy 70 points

    I have figured that the 0x0088 and 0x0098 is basically telling me that the gas gauge is entering into SLEEP mode as it is detecting 0 mA of average current. Totally makes sense. Also, the switching between the two bit values basically tells that the gas gauge is trying to detect any current at regular intervals ( in seconds ) and if it is not detecting, it goes back to SLEEP (0x0098). Please confirm and correct me if I am wrong.

    One thing still needs explanation is if this is something on the charger side. Right here is something that I noticed in the BQ25798 datasheet. 

    We haven't changed anything on the default settings of the BQ25798EVM except charge current values which are fast charge current and ITerm. Nothing on the tSafety. The default settings for it is 12h. We are seeing the current go down from the charger at 8.11 hrs which is what the nominal charge safety timing accuracy says. But here as you can see : 

    It says 12H. Why the discrepancy? Is the charger realizing that it is charging a battery pack for a long time now and triggers a safety request indicating maybe something wrong with the battery pack? Do we need to reset the charger with firmware after this 8H mark? Please advise.

  • 0 in reply to Pushpendra Singh
    TI__Guru 56146 points

    The gauge will enter sleep mode, if sleep mode is enabled and if the current (which is converted once a second) drops below the sleep mode current threshold.

    Note that the gauge will not measure current continuously when it is sleeping. It will wake up only if the current exceeds a threshold or periodically (the interval can be configured with sleep measure time). So this can lead to loss of coulomb count, if you let the gauge sleep in a system where there's significant current present but not enough to immediately wake up the gauge.

    I'll re-assign this to the charger team for your second question.

  • +1 in reply to Dominik Hartl11
    TI__Guru**** 155606 points

    Hi Pushpendra,

    The charger safety timer is only a counter and does not reset itself to a different value than default.  It can slow itself to 2X (i.e. set to 12 hours but potentially take up to 24 hours) if one of the current limiting features (DPM, thermal reg, TS WARM or COOL) is active. 

    Regards,

    Jeff