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TCA4311A: Cable extension for I2C communication line

ACGUY
Guru 11170 points
Part Number: TCA4311A

Hello E2E,

Our customer has plan to use the TCA4311A for two new boards.
The two boards communicate with cables of about 10 m. The protocol is i2c.

Please attached file. Their boards can't communicate properly.

Question and Request,
   -   Figure-13 of datasheet, did this circuit operate properly?
   -   Please let me know the design missing point for attached file circuit.

Regards,
ACGUY

TCA4311A_input_output.pdf

  • 0
    TI__Guru 72901 points
    Hey ACGUY,

    "Please let me know the design missing point for attached file circuit."
    The customer design looks a bit blurry, is it possible for you to get us a more clear picture? Also, it would be nice if we could look at the clock signals.

    "did this circuit operate properly?"
    Judging from the SDA waveforms, it looks like Yellow and Green do not match like they should. Are you able to provide us with what the Master device is? Did the master generate the Yellow waveform?

    Thanks,

    -Bobby
  • 0
    TI__Guru 74252 points
    ACGUY,

    One of the limitations for I2C is the amount of bus capacitance, in this application circuit with the TCA4311A can handle up to 1nF of capacitance on the bus. Is there any way you can provide the nominal capacitance for the cable? It's typically listed as pF/m.

    It looks like the rise time on the green and pink waveforms is slightly slower than the yellow waveform, and this is most likely due to higher pull up resistance and increased bus capacitance due to the long cable. You can see in the yellow waveform a faster rise time when the voltage reaches about 0.6-0.7V; this is the rise time accelerators turning on to boost the signal up to the appropriate logic level. When the green and pink waveforms reach this point however, they stop rising and hold the voltage steady.

    I noticed in the customer design that they have 10k pull ups on the cable, and 6.9k pull ups outside the cable, is there any way the customer can swap these values and then look at the signal? Or just place lower value pull ups on the bus cable and report back with the results?

    Another helpful piece to the puzzle would be zoomed in oscilloscope shots, so we can see the exact rise times of each waveform, is there any way the customer can provide this?

    Regards,