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BQ76940: BQ76940+BQ76200+BQ78350，charging is not working

user5811580
Intellectual 700 points
Part Number: BQ76940
Other Parts Discussed in Thread: BQ78350, BQ76200, , BQSTUDIO, BQ78350-R1

I just want to make a BMS made up of BQ78350+BQ76200+BQ76940, using 15 Li-PO batteries.

After powered on, BQ78350 can communicate with bqStudio by EV2300 normally.

Just download the right firmware to BQ78350,which is downloaded from ti.com.

According to the TRM of bq78350, just enable 15 batteries and 3 temperature sensors and the voltages of these 15 cells are right. The temperature showed on bqStudio is also right.

But DSG and CHG are disabled by default. Just enable FET_EN manually, DSG and CHG are enabled and the load current is also right when the load is on.

Question1: Because of enabling FET_EN manually, DSG is always on. When the charger is on, AFE_OVRD will occur. For the testing of charging, I have to disable FET_EN manually.

However,how does the BMS work without bqStudio?

Question2:During the process of charging, the charging current it very low, only 6mA. The voltage of the batteries is almost 58.4V and the charger is almost 60V.

Would you please give me some suggestions?

What should I do now?

The data of bqStudio is lised as below:

  • 0
    TI__Guru* 81034 points
    Hi,

    The CHG and DSG FETs are intended to protect the battery system during a fault condition and both should be enabled normally.
    The AFE_OVRD flag indicates that the BQ76940 has seen an OVRD_ALERT. This indicates that something in the system has pulled the ALERT pin high. (See Section 7.3.1.3.4 of the BQ76940 datasheet for detailed description. Special care must be taken so that this pin does not accidentally get pulled high - a 1 Mohm pulldown resistor is recommended).

    For the charging issue you describe, I think you are saying the charger has gone down to 6mA charging current because the cells are fully charged. I think the CHG FET is opening due to overvoltage protection triggering. I notice the individual cell voltages in your image are showing wide voltage variation - Cell 12 is showing 4310mV. The COV bit in the Safety Status register is high which confirms overvoltage is detected.

    Two things that may help (I am not sure if you are doing these already):
    - Make sure you run calibration for each cell as described in the EVM User Guide. This will ensure the measurements are accurate for your board.
    - Enable Cell balancing. (See Chapter 7 of the BQ78350-R1 Technical Reference Manual). This should be enabled by default.

    Best regards,
    Matt