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TCA9803: Attaching local device to A side

k1mgy
Expert 1680 points
Part Number: TCA9803

I intend to use the TCA9803 to insure robust I2C comms to an environmental sensor located about 16cM from my main board.  The same I2C bus (3.3V) serves an ADC device located on my main board.  I was tempted to attach the ADC to the A side and use the B side for my remote sensor (the ADC is only 1cM away from my CPU).  Is best practice to put all I2C devices on the B side (with the A side attaching to my CPU I2C port?).

  • 0
    TI__Guru 62920 points
    Hello,

    It is fine to have I2C devices on either side of the TCA9803 buffer. This part is often used to facilitate communication between two buses that operate at different VCC levels, and so generally it makes sense to group devices together based on their supply voltage. Let me know if I've misunderstood your question, though.

    Regards,
    Max
  • 0 in reply to Miguel Robertson
    Expert 1680 points
    I'm not using this part to level translate, but rather to fortify the I2C bus as the B side will service a long line. My instincts suggest keeping the bus master on the A side and peripherals on the B side, given the B side sources (and sinks) current, offering cleaner signal transitions...
  • 0 in reply to k1mgy
    Guru 317000 points

    If you put the ADC on the A bus, you can disable the buffer and the sensor's bus with the EN pin. (Don't know if that would be useful.)

    But otherwise, it does not matter. If the signal on the A bus is clean enough for the CPU and the TCA, then it is also clean enough for the ADC.

  • 0 in reply to Clemens Ladisch
    TI__Guru 62920 points
    To add on to Clemens's comments, it may make sense to place the ADC on the A side as well so that it does not need to interface directly to the cable. The cable could potentially add some capacitive loading that would distort the I2C signaling produced by the ADC.

    Max