• State Resolved
  • Locked Locked
  • Replies 6 replies
  • Subscribers 62 subscribers
  • Views 390 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

BQ27621-G1: BQ27621-G1 – I2C Bus Issue and Power Domain Recommendation

Tarek Sharbo
Prodigy 80 points

Part Number: BQ27621-G1
Other Parts Discussed in Thread: EV2400, BQSTUDIO

Tool/software:

Dear TI Support Team,

I’m experiencing an issue with the I2C communication on the BQ27621-G1 fuel gauge.

In my current design, the I2C pull-up resistors are connected to an external 3.3V LDO used elsewhere in the system. During initial testing, the fuel gauge communicated properly with BQStudio via the EV2400. However, the next day, BQStudio was unable to detect the device. Upon checking the I2C lines:

  • SDA is stuck at 0V

  • SCL reads 1.8V

  • No activity is observed on the bus using a logic analyzer

A new board shows SDA/SCL at 3.3V as expected, but I’m hesitant to connect it to the EV2400 for fear of causing similar damage.

Could you please advise:

  1. Is it safe to use 3.3V pull-ups on the I2C lines of the BQ27621-G1, or should they be connected to the internal LDO (1.8V) output?

  2. Would you recommend using a level shifter between the 3.3V host and the gauge to avoid potential backfeeding or damage?

  3. Any idea to solve the current problem, I tried to switch the power supply, but it didn't help.

I’d appreciate your guidance on how to properly interface the fuel gauge to avoid such issues in the future.

Best regards,
Tarek Sharbo

  • +1
    TI__Guru 70376 points

    1: Yes, this is safe. See d/s, 7.1. Max. voltage = 6V. Please do not connect anything other than a 2.2uF capacitor and optionally the BIN pull-up resistor (1.8MOhm) to VDD.

    2: Not necessary

    3: Make sure that your design doesn't violate the abs. max. values from the datasheet.

  • 0 in reply to Dominik Hartl11
    Prodigy 80 points

    Thank you for the clarification.

    In my current circuit, the absolute maximum ratings are not exceeded, but the I2C communication still doesn’t work, even though it was initially functional. To address this, in the new revision, I’ve modified the design to isolate the I2C bus and added a level shifter from 1.8V to 3.3V. As mentioned in the datasheet, both 1.8V (internal) and 3.3V (external) connections to the I2C bus are valid options.

    I’ve also included some unfitted components to allow bypassing the level shifter if needed.

    Please find the updated schematic attached. I’d appreciate it if you could review it and share any feedback or suggestions you might have.




  • +1 in reply to Tarek Sharbo
    TI__Guru 70376 points

    The schematics look fine. Did you check, if the I2C digital IO specifications between the bq27621 (table 7.6, datasheet) and you I2C host are compatible?

  • 0 in reply to Dominik Hartl11
    Prodigy 80 points

    I have confirmed the compatibility of the IC with our host MCU (ESP32) by checking Table 7.6 of the datasheet.

    I have a question regarding the functionality of the GPOUT pin. Is it required to be toggled by the host MCU under normal operating conditions? Or is its use limited to specific scenarios, such as indicating an I2C communication fault or waking the IC from sleep mode?

    I understand that the GPOUT is an open-drain pin, which can be configured to provide the system with the State of Charge (SoC) value interrupt. To avoid any risk of damage, I have ensured that the host MCU cannot send an output signal to this pin. My concern is that the MCU's push-pull output, if driven high while the GPOUT is in a low state, would create a direct path to ground, resulting in a short circuit that could damage one or both components.

    Considering this potential issue, what is the best practice? Should we avoid connecting the GPOUT directly to the host MCU if we are confident in the stability of our I2C communication?


  • +1 in reply to Tarek Sharbo
    TI__Guru 70376 points

    You do not need to toggle GPOUT in regular use. However, if the chip enters shutdown state, then you need to either power cycle the gauge or toggle GPOUT to get it out of this state.

    I would always advise to connect GPOUT to the host uC because that's the only 100% sure way to avoid having it stuck in a shutdown state.

  • 0 in reply to Dominik Hartl11
    Prodigy 80 points

    Now it's clearer. Thank you so much for your support.