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PCA9306: About I2C layout

Driscoll Tsai
Expert 1590 points
Part Number: PCA9306

Hi Sir,

In its DS page 14, the I2C layout recommend using fan out signal traces away from each other.

why can't using "differential traces"? has any purpose?

thanks~

Regards,

Driscoll

  • 0
    TI__Mastermind 49270 points

    Hello Driscoll,

    The reason why we recommend you fan the signals away from each other is to avoid cross talk between the two lines. A lot of the time, we see when SCL/SDA changes, part of the signal jumps to the other signal. If you run the signals next to each other, you basically will have a conductor (trace) next to an insulator(part between the traces) and another trace (conductor). This forms a parasitic capacitance between the SDA/SCL lines where the fast falling edges can affect the signal (as well as fast rising edges).

    Thanks,

    -Bobby

  • 0 in reply to BOBBY
    Expert 1590 points
    Hi Bobby,

    Thanks for you quick reply.
    BTW, how about the distance between SCL and SDA?
    Beside PCA9306, the other I2C layout is also follow this way (fan-out)?
    thanks~

    Regards,
    Driscoll
  • 0 in reply to Driscoll Tsai
    TI__Mastermind 49270 points

    Hello Driscoll,

    "BTW, how about the distance between SCL and SDA?"
    Distance between the two doesn't need to be that large in my opinion. Ideally further is better but maybe around ~50mills from each other would be sufficient.

    "the other I2C layout is also follow this way (fan-out)?"
    That is correct.

    -Bobby