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BQ76930: Is breaking after a while in operation mode, please help us and review our schematic

Florian Seibold62
Prodigy 20 points
Part Number: BQ76930
Other Parts Discussed in Thread: TIDA-00449,

Hello,

we develope a battery management system with an BQ76930 as battery management controller. After connecting the prototypes to the battery everything seems to be fine:

V_CAP ~ 3.3V

V_RegOut ~ 2.5V

I2C Communication is ok

=> Everything is fine.

After doing I2C Communication for a few hours (without charging or discharging) the bq dies:

V_CAP ~ 0V

V_RegOut ~ 0V

I2C Communication is not available

=> Worst case.

Gen_01_PART_NAME_SCH_Standard_Schematic_03_SCHEMATIC_VERSION.PDF

Can you please review the bq relevant parts of our schematic and give me feedback?

Thanks a lot. Florian

  • 0
    TI__Guru 54715 points
    Hi Florian,
    R22 was a current shunt resistor on the EVM, it would not be needed and could be shorted.
    I don't see a power filter for the BAT pin, a 1k from C10 net to BAT pin of IC1 with a 10 uF from BAT to VC5X.
    So the BAT pin of the bq76930 does not seem to have a power filter. I don't know if that would cause a shutdown, it could give very strange readings causing the MCU to send a shutdown. You might correct this and/or check the behavior of the MCU, perhaps monitor the commands sent to the bq76930 before power goes off.
  • 0 in reply to WM5295
    Prodigy 20 points

    Hi,

    Thanks for your help. I changed the schematic as you recomended to the following one:

    Bmc_Update_20190123.pdf

    I also remplaces the populated BQ to a new one to check if it's broken. The new one doesn't boot, too.



    I removed the BQ relevant code, too. Now the microcontroller doesn't send anything to the BQ. I still have no voltage on V_Regout or V_Cap after reconnecting the battery voltages.

    Do you have another idea? Can it be possible, that I break the BQ? Do you have ideas how that could happen?

    Thanks a lot.

    Best regards,

    Florian

  • 0 in reply to Florian Seibold62
    TI__Guru 54715 points
    Hi Florian,
    The power connection for the BAT pin is still not correct. Power for BAT and the REGSRC supply circuit should come from the battery+, Cell10pos. In the bq76930EVM user guide notice the connection of R22, R58, and R77 to net C10. In TIDA-00449 notice R1, R3 and D1 all connect to net C10. When using TIDA-00449 as a reference, note that C21 is not connected as recommended in the data sheet. You have your C21 connected correctly to VSS (BAT_GND).
    In the schematic I don't see a connection problem which would prevent boot or have caused the shutdown described earlier. C4 and C13 on the TSn pins have a 4U7 designation same as the REGOUT capacitor. The EVM and many designs use a 4.7nF cap on TSn, 4.7uF will be too large for TSn, it could prevent a proper rising edge for boot depending on the source or hold a voltage on the pins to prevent boot or proper start of the top group.
    Measure voltages, compare to the data sheet and schematic and find the missing voltages, connection, or event.