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BQ25720: I2C pins shorted to grounded after disconnecting BQ25720 PCB from MCU PCB

Alexandru Marin
Prodigy 10 points
Part Number: BQ25720


Tool/software:

In our design, we have two PCBs: one with the BQ25720 charger IC and the other with an STM32 MCU.

We’ve encountered an issue where disconnecting the BQ25720 PCB appears to cause the I2C pins on the charger to short to ground, resulting in irreversible damage. Based on our testing, ensuring a consistent ground connection between the two PCBs during disconnection seems to prevent this problem. However, we cannot always guarantee a ground connection during PCB disconnection in the final design.

Both PCBs already include TVS diodes on the I2C pins.

What could be causing this issue, and what additional measures can we take to protect the I2C pins from damage during PCB disconnection?

  • 0
    TI__Mastermind 34905 points

    Hi, Alexandru,

    This is weird. I don't think this is related to BQ25720. When connecting SMBUS, try three wires only - SDA, SCL and GND. 

    Regards,

    Tiger

  • 0 in reply to Tiger Zhou
    Prodigy 10 points

    Hello Tiger,

    Thank you for your response.

    The battery remains connected to the BQ25720 when we disconnect the MCU PCB. Between the two PCBs, we only have SDA, SCL, and GND connections. Additionally, the pullup resistors are located on the MCU PCB.

    My assumption is that disconnecting the BQ25720 PCB from the main PCB also disconnects the ground, which might be causing issues on the SDA and SCL lines. What measures could I take to better protect these pins on the BQ25720 side?

  • 0 in reply to Alexandru Marin
    TI__Mastermind 34905 points

    Hi, Alexandru,

    We always plug and unplug the SMBus connector from BQ25720 PCB, without any issue. SDA/SCL are open-drain lines with 1K-10K pull-up resistor. 

    You can protect the line with schottky diodes like below. 

    Regards,

    Tiger