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BQ25892: BQ25892 Not working without battery, battery doesn't seem to charge.

der.uLe
Prodigy 30 points
Part Number: BQ25892

Hello,

I would like to use the BQ25892 in default mode (no host) with the following design:

My objective is to power my device from the USB line while charging the battery (LiPo 3.7V 1300mAh), the device should be powered when no battery present or directly from the battery when the USB line is not connected. From the documentation I am not sure if all this scenarios are possible without a host.

So my first question is, are all this scenarios possible without host ? if not which ones are and is there cases where the functionality would be impaired? (e.g. compulsory power cycle after the 12h watchdog timer have run out, etc.)

While validating the design with our prototypes, the output of the pin SW was 0.7V when no battery was connected to the system and the input VBUS was 5V from a power supply with ample reserve. From other post in this forums I have been able to deduce that this should not be the case, but I haven't been able to find the reason why this could happen.

After connecting the LiPo to the system and keeping the VBUS input at 5V the output SW was 3.75V, the same voltage as the LiPo, however, this voltage never increased even after an hour of being connected, as I expected if the LiPo was to be charged.

My second question is, how do I go about to troubleshooting this problems without a host interface?

Looking forward to your answer, thank you for your support.

  • 0
    TI__Mastermind 46551 points

    Hi,

    Referring to 9.2.7.1 Autonomous Charging Cycle, with battery charging is enabled (CHG_CONFIG bit = 1 - default and CE pin is low), the device autonomously completes a charging cycle without host involvement per the device default charging settings. Please check the default settings listed on Register Maps on the d/s and see if the default settings fit your application and batteries being used.


    It will be easier to debug with reading register values via I2C. If not using I2C, please check if STAT and/or INT indicate any faults and debug from there. Please also check if the input source is over-loaded, either the current exceeds the input current limit or the VBUS pin voltage falls below the input voltage limit. Please refer to 9.2.6.2 Dynamic Power Management on the d/s for the details.

    Please visit https://e2e.ti.com/support/power-management/f/196/t/874557 for BQ2589X: Schematic Review and PCB Layout Design Tips and https://e2e.ti.com/support/power-management/f/196/t/875386 for BQ2589x/BQ25898x FAQs.

    Please watch the video below for charger operations and valuable tips.

     Battery charger system overview (training.ti.com/battery-charger-system-overview

    Battery Charger Common Issues: Why my Battery is Not Charging (training.ti.com/battery-charger-common-issues-why-my-battery-not-charging


    Thanks,

    Ning.

     

  • 0 in reply to Ning T
    Prodigy 30 points

    Hi Ning,

    thank you for the pointer, they where pretty informative and as a result I've been able to clear some of the questions that I had, however, in reference to:

    Referring to 9.2.7.1 Autonomous Charging Cycle, with battery charging is enabled (CHG_CONFIG bit = 1 - default and CE pin is low), the device autonomously completes a charging cycle without host involvement per the device default charging settings. Please check the default settings listed on Register Maps on the d/s and see if the default settings fit your application and batteries being used.

    Looking at the Table 5 in the datasheet, the only condition that is not compatible with my battery is the 2.048A Charging Current, but I assume that the charging current still will be the lower value between the internal registers (2.048A) and the current set by the ILIM resistor. Is that the case ? Will the charging current still be 2.048A if PSEL is pulled up to the SYS voltage? If the charge of the battery successfully finishes before 12h, will a new charge cycle will start when the battery voltage comes below recharge threshold again?

    Thank you.

  • 0 in reply to der.uLe
    TI__Mastermind 46551 points

    Hi,

    1. The actual input current limit is the lower limit set by ILIM pin (when EN_ILIM bit is high) or IIINLIM register bits. Input current limit of less than 500 mA is not support on ILIM pin.

    The device features Dynamic Power Management (DPM). When input source is over-loaded, either the current exceeds the input current limit (IINLIM or IDPM_LIM) or the voltage falls below the input voltage limit (VINDPM). The device then reduces the charge current until the input current falls below the input current limit and the input voltage rises above the input voltage limit. Please refer to 9.2.6.2 Dynamic Power Management on the d/s for the details.

    2. When a full battery voltage is discharged below recharge threshold (threshold selectable via VRECHG bit), the device automatically starts a new charging cycle.

    Thanks,

    Ning.

  • 0 in reply to Ning T
    Prodigy 30 points

    Hi,

    thank you very much, with this are my issues solved and the device is working as designed.

    Best regards,