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BQ25713: How to increase battery charging current as state of charge increases

Sudha Nayak S
Intellectual 380 points
Part Number: BQ25713
Other Parts Discussed in Thread: BQ34Z100, , BQSTUDIO

Hi,

We are using BQ34Z100 as a gauge-meter along with BQ25713 as part of main charge control IC in our battery back up based design.

Battery used is 2-terminal 3SP1 with 10.7V as max voltage.

Currently we are performing learning cycle and to capture the log information we are using BQStudio.

We captured the log while battery is charging, initially charging current was 370mA and as state of charge increased,0434.battery_charge_log.csv charge current got decreased (below 50mA), because of that it was taking more time to charge the battery.

Please find the attached .csv file for the same.

We are using following register setting

ChargeCurrent() [Reg 0x03/02] - 1A

ChargeVoltage() [Reg 0x04/05] - 10.7V

InputVoltage() [Reg 0X0B/0A] - 2V

IIN_HOST() [Reg 0x0F/0E] - 3.3A

MinSystemVoltage() [Reg0x0D/0C] - 10.7V

Could you please give any solution on how to increase charging current ?

Thanks and Regards,

Sudha Nayak

  • 0
    TI__Mastermind 32745 points

    Hi, Sudha,

    The charge current decreases when it reaches max charge voltage, thus operates in constant voltage charging mode. Suggest raising the max charge voltage to 12.6V according to the battery specification. The max charge voltage is usually higher than the min system voltage 10.7V. 

  • 0 in reply to Tiger Zhou
    Intellectual 380 points

    Hi Zhou,

    As you have suggested, I have set max charge voltage to 12.6V and battery charging current increased as expected, however we are facing problem during charging.

    We have bq34z100 battery gauge to read the battery information using BQstudio.

    When we completely discharge the battery and when we connect main supply to charge the battery, it is not charging and we are reading current information in bqstudio as 0 mA.

    Are we missing any register settings in BQ25713 that is not allowing to charge the battery?

    Thanks and Regards,

    Sudha Nayak

  • 0 in reply to Sudha Nayak S
    TI__Mastermind 32745 points

    Hi, Sudha,

    To start charging, you may need to set the charge current and charge voltage registers. See BQ25713 quick start guide. 

    https://www.ti.com/tool/BQ25713EVM-017

  • 0 in reply to Tiger Zhou
    Intellectual 380 points

    Hi Zhou,

    I have already set those registers.

    MinSystemVoltage() [Reg0x0D/0C] - 10.7V [0x2A00]

    IIN_HOST() [Reg 0x0F/0E] - 3.3A [0X4100]

    InputVoltage() [Reg 0X0B/0A] - 2V [0x0800]

    MaxChargeVoltage() [Reg 0x04/05] - 10.7V [0x3200]

    ChargeCurrent() [Reg 0x03/02] - 1A [0x0400]

    While testing we have captured following readings for BQ25713

    1) When for the first time, Main power supply and battery is connected [Battery starts charging]

    MinSystemVoltage () = 0x2A00

    IIN_Host() [ Input Current Limit] = 0x4100

    InputVoltage () [input voltage Limit] = 0x0800

    MaxChargeVoltage () = 0x3200

    ChargeCurrent () = 0x0400

    ADCVSYVBAT() = 0X7C7C

    2) When we remove Main power supply and only battery is connected [Battery starts discharging]

    MinSystemVoltage () = 0x2A00

    IIN_Host() [ Input Current Limit] = 0x4100

    InputVoltage () [input voltage Limit] = 0x0800

    MaxChargeVoltage () = 0x3200

    ChargeCurrent () = 0x0000

    ADCVSYVBAT() = 0X6364

    3) When for the second time, Main power supply and battery is connected [Battery will not charge]

    MinSystemVoltage () = 0x2A00

    IIN_Host() [ Input Current Limit] = 0x4100

    InputVoltage () [input voltage Limit] = 0x1D00

    MaxChargeVoltage () = 0x3200

    ChargeCurrent () = 0x0400

    ADCVSYVBAT() = 0X7D6F

    When we are trying to reconnect Main supply for the second time, battery is not getting charging and InputVoltage() value is changed to 0X1D00 from 0x0800.

    Please guide us on how to resolve this issue?

    Best Regards,

    Sudha Nayak

  • 0 in reply to Sudha Nayak S
    TI__Mastermind 32745 points

    Hi, Sudha,

    This is an expected behavior. To protect the battery from unintentional charging, please set the charge current and charge voltage again when reconnecting your main power supply. 

  • 0 in reply to Tiger Zhou
    Intellectual 380 points

    Hi Zhou,

    After setting charge current again, we are able to charge the battery after connecting main power supply for the second time.

    Thanks and Regards,

    Sudha Nayak