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BQ51021: I2C when chip is not powered

Part Number: BQ51021
Other Parts Discussed in Thread: BQ51221

Hello,

I wanted to double check something regarding this part and I2C. Since the bq51021 is only powered by the wireless power coil, the chip is without power whenever it is not on a charging pad. The I2C bus will have some other devices powered on and communicating on the bus while the bq51021 is powered down.

Can you confirm that the powered-off bq51021 won't interfere with the I2C communication of the remaining devices on the bus?

Thank you,
Ryan B. 

  • Hi Ryan
    The BQ51021 internal circuits are powered from the RECT pin, this is rectified AC1 / 2 input. When not on the charging pad the device is powered down, will have no activity on the bus.
    Customer may want to check this to make sure some parasitic element is not causing issues. This can be checked with the BQ51221 EVM which is very similar to BQ51021, I2C bus wise.
  • Hi Bill,

    Thanks for helping with this question.

    Currently we aren't experiencing any issues. However, before one of our customers releases their design, we wanted to confirm if we needed an I2C switch to put the bq51021 on it's own SDA/SCL lines.

    We are worried that high dV/dT on the I2C lines will cause the self-turn on effect of the internal open-drain FET.

    I'm assuming since this device is meant to be connected and removed from power in everyday applications, that we have worked on designs previously where the bq51021 was placed on the same I2C bus as always-on devices (unless of course that proved to be a problem).

    Has this been done in the past? Or did we purposely put the bq51021 on it's own I2C lines? Thank you!

    Regards,
    Ryan B.
  • Hi Ryan
    I will email you and we can discuss this more.