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BQ76942: bq76942 Battery Management System, communications issue

Hiroshi Ransom
Prodigy 30 points
Part Number: BQ76942

Hi TI,

We have a bq76942  Evaluation board and are having difficulty operating it over I2C using the Arduino I2C library (Wire).

Reg1 has been configured for 5V, with the Pullup jumpers applied on SDA and SCL.

Our setup uses the below circuit with smaller resistors for logic level shifting.


We have a nice waveform at 400kHz and at 3v3.



Can you make any suggestions on how we can establish communications?

I can see that the first command sent to the device should be: SET_CFGUPDATE 0x0090

We did some testing with a oscilloscope and this board is showing waveforms which are 20kHz or 80kHz however the datasheet says it should start up with waveforms at 400kHz.

Thanks,

-Hiro

  • 0
    TI__Mastermind 42060 points

    Hello Hiro,

    I'd suggest to use a logic analyzer to see what is being seen on the I2C lines of the EVM.

    The BQ769x2 Software Development Guide shows examples on how communication should look.

    For the level-shifting circuit, you must ensure that you use FETs with small gate-source threshold voltage. Does your host MCU support clock stretching? Typically clock stretching is required to ensure proper communication.

    Best Regards,

    Luis Hernandez Salomon