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TXB0104 fanout I2C

Mike Wang2
Intellectual 2760 points
Other Parts Discussed in Thread: TXB0104

Hi team,

My customer wants to use TXB0104 to do a 1:2 fanout for I2C signal, as below:

two channels are tied together as fan out function. Do you think this design is correct?

BR,

Mike

  • 0
    TI__Guru 62480 points
    Moving to voltage translation forum for support .
  • 0
    TI__Expert 6335 points
    Mike,

    TXB devices are not appropriate for open-drain interfaces such as I2C. TXS devices should be selected instead.

    For auto-direction translators, shorting I/Os together is not recommended. Keep in mind that each data pin functions as an input AND as an output. So when you short two data pins together, you are also shorting an output of one pin to the input of another pin (and vice versa). This can cause erroneous data trasmission. An example of such an erroneous event is explained below:

    1. An external device drives pin B3 to Logic High
    2. This causes the translator to drive pin A3 to Logic High
    3. Since pin A3 is shorted to pin A4, then pin A4 is driven to Logic High
    4. This causes the translator to drive pin B4 to Logic High, which is an error!

    Best Regards,
    Nirav
  • 0 in reply to Nirav Patel
    TI__Intellectual 2760 points

    Hi Nirav,

    Thanks for your reply.

    But for I2C, the B3 and B4 pin should originally be connected together., as I2C supports multi-load condition. Customer didn't do that because the signal integrity was not good if B3/B4 are tied together. They want to use TXS0104 to improve the signal.

    Do you see other issues here?

    BR,

    Mike

  • 0 in reply to Mike Wang2
    TI__Expert 6335 points
    Mike,

    My previous comment about shorting I/Os on the TXB devices also applies to the TXS devices. In addition, each I/O has a rise time accelerator, and shorting those together is not recommended.

    Can the custome consider our I2C translators/repeaters instead?

    Best Regards,
    Nirav