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Original question:

BQ24773: Individual Cell Balancing in a 4 cell pack and State of Charge(SOC) monitoring

Compiler/BQ24773: BQ24773 I2C

David chen
Expert 1200 points
Part Number: BQ24773

Tool/software: TI C/C++ Compiler

Now I USE I2C driver the BQ24773 has a problem. When I  not connect the battery, I only provide the adapter power supply. After MCU sends disabled charging function data (ChargeOption0() sends 0x67CF), the power output of the whole system is turned off? how to Solve the problem?

  • 0
    TI__Genius 11850 points
    Hi David,

    Just to clarify, are you saying that with the adapter connected, no battery connected, and charge disabled, VSYS = 0 V?

    What is VSYS when charge is enabled (before the MCU disables charge)? What are your minimum system voltage and maximum charge voltage register settings? Are you testing this on an EVM or your own circuit?

    Best regards,
    Angelo
  • 0 in reply to Angelo Zhang87
    Expert 1200 points
    1. Just to clarify, are you saying that with the adapter connected, no battery connected, and charge disabled, VSYS = 0 V?-----YES
    2. VIN 19v, to 3S bat charge,test in my circuit,when charge is enabled, VSYS is normal, I set VSYS MIN=10V，Vsys max=13.5V;
  • 0 in reply to Angelo Zhang87
    Expert 1200 points
    HI Angelo:
    In the datasheet,there is not have how to use in no Battery describe ,could you pls help to share it for me?
  • 0 in reply to David chen
    TI__Genius 11850 points

    Hi David,

    Thanks for the clarification. I just tested this on an EVM and got similar results for #2. However, for #1 (no battery connected), VSYS should be set by your maximum charge voltage register. This is true whether charging is enabled or disabled.

    One possible reason that your VSYS falls to 0 V is if the charger enters SYSOVP (see Section 8.3.10.4 in the datasheet for more details). SYSOVP causes ACFET and RBFET to latch off, so with no battery connected, VSYS will fall to 0 V. I was able to get VSYS to fall to 0 V on the EVM if I entered SYSOVP.

    To confirm whether or not SYSOVP is the issue, please check bit [11] in register ChargeOption0 right after VSYS falls to 0 V. Also, please double check your CELL pin configuration, as this sets the SYSOVP threshold. Is the CELL pin pulled low, floating, or pulled high?

    To answer your last question, here's a waveform showing the behavior with no battery and no system connected. Yellow is VSYS and green is VBAT. When I plug in the 19 V adapter, VSYS rises up to my max charge voltage register setting (9 V), and VBAT oscillates as the BQ24773 performs float charging and continuously enters charge/recharge cycles. I then disabled charging, which caused VBAT to fall to 0 V while VSYS was still regulated to 9 V. Finally, I enabled charging again, and float charging resumes.

    Best regards,

    Angelo