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Original question:

BQ24192: Charging safety timer

BQ24192: Charge Termination

Janhavi Rane
Prodigy 170 points
Part Number: BQ24192
Other Parts Discussed in Thread: BQ27531-G1, , BQSTUDIO

Hello,

We are using BQ27531-G1 along with bq24192 charger. Our circuitry as follows:

As per the circuitry, rechargable Li-ion battery is connected to the BAT pin of bq27531-g1 gas gauge. External 5V power supply is connected to the VBUS pin of charger and SYS pin provides voltage to the system. During the test when device is on with external power supply, we observed in bqstudio that when FC bit set (battery capacity :100%) DSG bit also sets at the same time and it starts to discharge the battery for few mintues and then it clears both the bits and start to charge again.

From this test, we understand that when rechargeable battery is full , VBUS disconnect the connection with external power supply and system runs via battery. Did we understood correctly? is chager works like this when battery is full?

Regards,

Janhavi Rane

  • 0
    TI__Mastermind 24075 points

    Hi,

       The converter should still supply SYS when battery is fully charged, and valid VBUS is connected.

  • 0 in reply to Kedar Manishankar
    Prodigy 170 points

    Hello Kedar,

    Thank you for your reply. But still some terms in charger are not clear for us. 

    We are using this charger in one of our medical device where in most of the cases the device will remain continuously on with rechargeable battery and external power adapter.

    As per the functional block diagram, pg 12 (bq24192 SLUSAW5B –JANUARY 2012–REVISED DECEMBER 2014 datasheet, ) and after performing test we observed that, (RBFET, Q1) switch will open and the system will be powered  by the rechargeable battery  (BATFET Q4 is closed) when FC bit is set.

    During this process battery is discharging in small amount(from 100% to approx. 98%) and charge again (from approx. 98% to 100%) even though power adapter is connected. From the log data(which is attached below), we have seen that during one day accumulated discharge is more than our CC threshold(4000) which is effectively increasing the battery charge cycle count. Is this complete behaviour correct?  Why the battery is repeatedly discharging till approx.98% and start to charge again?

    Which settings we need to adapt to overcome this issue ? As frequent cycle count increment (per day) is not good in our use case where power is continuously connected. 

    We just want to know how charger works when rechargeable battery is full and external power supply connected. We are seeking support from TI in this subject as our device is in approval process.

    I am attaching log and gg file below for more information.

    Performance test_charge cycle count_24.08.log

    also gg file:

    2475.Board_15.gg.csv

    Thanks in advance.

    Regards,

    Janahvi Rane

  • 0 in reply to Janhavi Rane
    TI__Mastermind 24075 points

    Hi Janahvi,

       Battery applications prefer having battery fully charged as long as adapter is connected, to maximize run time whenever the adapter is removed and the battery has to solely power the system. This is called recharge threshold and you can read more about it in the datasheet. Below is the EC table snippet from the BQ24192 datasheet:

  • 0 in reply to Kedar Manishankar
    Prodigy 170 points

    Hello Kedar,

    Thank you. How to change VRECHG (REG04 (0) ) to 100 mv ? In our case gauge is controlling the charger. As per the bq27531-G1 gas gauge datasheet, the battery recharge threshold from the bq24192 charger is not used here. The gauge controls the recharge function based on the FC Clear % or FC Clear Volt thresholds.

    Regards,

    janhavi Rane

  • 0 in reply to Janhavi Rane
    TI__Mastermind 24075 points

    Hi,

       Your host controller can configure that register value. Alternatively if gauge is handling all of the termination, then you can just disable termination from the BQ24192 charger through REG0x05 bit 7

  • 0 in reply to Kedar Manishankar
    Prodigy 170 points

    Hello Kedar,

    Thank you so much for your support. We found an error as in our case CHGTRM_HIZ bit was enable therefore after full charging the charger was going in HIZ mode and the system was powered by the battery.

    We have disabled the CHGTRM_HIZ bit and now cycle count is not increasing anymore with continuous external power supply.

    Have a nice weekend. 

    Regads,

    Janhavi Rane