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BQ76940: i2c communication lines went down when connected with micro controller i2c lines

Satish
Prodigy 40 points
Part Number: BQ76940


We have BQ76940EVM with BQ7694000DBT chip on it, and successfully communicated with the I2C communication.

Now we developed the same circuit with BQ7694003DBT chip, but when ever micro controller I2C bus is connected to the circuit then immediately SDA & SCL lines got low and raised to normal level when disconnected

the same micro controller & firmware was working successfully with EVM again.

  • 0
    TI__Expert 6085 points
    Check the exact version of the bq76940. There are 2.5V and 3.3V. On the EVM the bq76940 (depending on the ver) is REGOUT=2.5V is selected to be compatible with 2.5V Gauge. On your design, The I2C communication of the SCLK, SDATA lines may need > Vih of the bq76940. Most uC go from 0-5V. Thus may not see the 3.3V as a valid logic High. Check the uC I/O spec and configuration.
  • 0 in reply to Vish Nadarajah
    Prodigy 40 points
    As we mention in the problem description, we are already communicating with the EVM module which has BQ7694000DBT(2.5V), and we develop one more Board with BQ7694003DBT(3.3V). For testing we have a MCU Board where the I2C lines connected to EVM and worked perfectly, but the same setup is failed when connected to the 3.3V developed board.
    The final point is when we are connecting the MCU to EVM, i2c communication is good; when the same setup is connected the developed board, i2c lines went low.
  • 0 in reply to Satish
    TI__Expert 6085 points
    Please check the input logic of the MCU. the bq769X0 is NOT seeing the logic 1 from the MCU. the Vih needs to be revisited.

    EVM1 , I2C is configured( pullup) to 2.5V; EVM1 worked with the MCU Board. Good job!
    EVM2 is i2C configured(pullups) to 3.3V. EVM2, I2C communication is failing with MCU. am I correct in the summary?