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

Part Number: ISO1640
Other Parts Discussed in Thread: PCA9306

In this 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?

  • Hi Christian,

    Thank you for posting, and welcome to E2E! If complete isolation is not necessary in this application, the ISO1640 and other digital isolation devices can be used with a shared GND connection to enable the use of two separate power supplies with the same GND reference, as you mentioned. It is okay to use the device this way, and there will not be any current flow from either power supply to the other through the ISO1640; it could even be configured in such a way that the power supplies are at different voltage levels as mentioned in this FAQ:



    ISO1640 and other digital isolation devices are not meant to share GND, signal, or Vcc connections across each side of the isolation device to preserve optimal isolation protection by the device, but as mentioned above, this can be done and the isolator will prevent current flow from Vcc1 to Vcc2 and vice versa.

    Please let us know if you have additional questions.


    Respectfully,
    Manuel Chavez

  • Hi Manual,

    Thank you for welcoming me to E2E and for your reply! Due to supply concerns for the ISO1640, the PCA9306 device is being considered.

     Can you confirm that the PCA9306 device will also work in this same use case?

    Thanks,

    -Christian

  • Hi Christian,

    You're welcome! PCA9306 should work in this same application without isolation protection, but please do confirm this by asking the supporting team on E2E. The device packages for ISO1640 and PCA9306 are not identical, but either of the devices can still work so long as the corresponding pins are connected on the PCB layout.

    You can create a new or related thread using the red and yellow buttons in the top corner of this window or the link below:
    https://e2e.ti.com/p/addpost?rt=1024318

    Please ensure to list the part number as PCA9306, and let us know if you have any follow up questions.


    Thank you,
    Manuel Chavez