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BQ24192: Is it normal that battery is discharged when adaptor is connected?

Nils Larsen
Prodigy 70 points
Part Number: BQ24192
Other Parts Discussed in Thread: BQ27531-G1,

Hello,

We're using the charger bq24192 together with the fuel gauge bq27531-G1 in a product.

The question is about the case when an adaptor is connected (VBUS=5,1V) and a charging cycle has just been terminated sucessfully. In case it matters, we have programmed the charging voltage to 4,05V and termination occurs when charging current drops below 120 mA.

Until recently, we were expecting for this case:

  • Charging stops
  • VSYS stays at ~4,05V and is being powered from adaptor

However, we have seen that rather this happens:

  • Charging stops
  • VSYS stays at ~4,05V and is being powered from battery
  • After a while (~30 minutes), charging starts again

We have verified that Dynamic Power Management ist NOT active (the bit is not set and the adaptor is sufficently strong).

Is it expected behavior that the battery is discharged when an adaptor is connected? We observe an endless charge-discharge-cycle.
Can we influence if VSYS is being powered from battery or from adaptor? It would actually be great, if the host could configure this.

Thanks you in advance, best regards,
Nils

  • 0
    Prodigy 70 points

    BTW, here is a related question (answer was not posed in public): https://e2e.ti.com/support/power-management/f/196/t/606947

  • 0 in reply to Nils Larsen
    TI__Mastermind 46551 points

    Nils,

    Could you please provide these information when you think the operation is not abnormal?

    What are VBUS (voltage at VBUS pin), IVBUS, VSYS, ISYS, VBAT (voltage at VBAT pin), IBAT? Could you please provide all register values of the charger?

    Thanks,

    Ning.

  • 0 in reply to Ning T
    Prodigy 70 points

    Thank you, Ning, for the support.
    I have recorded those values and checked them. I could post them all, but I'm suspecting it has to do with EN_HIZ (bit 7 in REG00). I wasn't aware of this mode/feature before.

    EN_HIZ goes from 0 to 1 when the charging stops. I think BQ27531-G1 sets the bit, because I did not change the BQ27531-G1 default setting CHGTRM_HIZ=1 in "Charger Options".

    I'll change CHGTRM_HIZ and see what happens. Probably, VSYS will the be powered from adapter after charge termination (as I expected) and not from battery.

    If so, it leave me with just one question: Can I influence EN_HIZ when charger is controlled by BQ27531-G1 without re-flashing BQ27531-G1configuration? I would like the host processor to change the behaviour depending on external circumstances and avoid re-flashing each time.

    Best regards, Nils

  • 0 in reply to Nils Larsen
    TI__Mastermind 46551 points

    Nils,

    The host may modify EN_HIZ bit any time. Please note that In default mode, the device keeps charging the battery with 5-hour fast charging safety timer regardless of REG05[2:1] default value. At the end of the 5 hours, the EN_HIZ (REG00[7]) is set to signal the buck converter stops and the system load is supplied by the battery. Please refer to 9.3.3.6 Charging Safety Timer on the d/s for the details.

    Thanks,

    Ning.