• State TI Thinks Resolved
  • Locked Locked
  • Replies 2 replies
  • Answers 1 answer
  • Subscribers 33 subscribers
  • Views 591 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.

Original question:

ISO1640: Back feed current I2C passing between two 3.3V I2C domains

PCA9306: Back feed current I2C passing between two 3.3V I2C domains

Christian Greeff
Prodigy 680 points
Part Number: PCA9306
Other Parts Discussed in Thread: ISO1640,

Greetings!

In my customers application two 3.3V power domains are used. I2C signals need to be passed through these domains. 

Will this part still prevent back feed current in an application where V1 and V2 have the same source but come up at 100ms difference, i.e. V2 comes 100ms after V1 but both have same GND?

I received feedback that the ISO1640 device can do this, however I wanted to verify that the PCA9306 can as well.

Thanks so much,

-Christian Greeff

  • 0
    TI__Prodigy 680 points

    For more context,

    1. 3V3_MCU comes first
    2. 3V3_S5 comes after
    3. M0_I2C is connected to 3V3_MCU power domain source
    4. M0_I2C_SCL and M0_I2C_SDA connected to a I2C device powered by 3V3_S5.
    5. Trying to prevent current flow from the source (powered by 3V3_MCU) to the device (powered by 3V3_S5) through the I2C signals.
    6. FYI, the I2C device on 3V3_S5 is the master in normal operation.

    I would also appreciate feedback if any modification is needed.

  • 0
    TI__Guru 53575 points

    Hi Christian,

    The output pins (SDAx and SCLx) of PCA9306 will remain high impedance until both Vref1 and Vref2 are powered and the device is enabled via the EN pin. 

    There is a leakage path between Vref2 and Vref1 when the EN line is high. This leakage is limited by the required 200k-ohm resistor on this supply. So if Vref2 and EN come up before Vref1, there will be a small leakage path through this resistor. This is not a concern if Vref1 comes up first so long as EN remains low. 

    Let me know if you have any more questions.

    Regards,
    Eric Schott