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I plan to use an I2C extender over 30 meters. I am left with no choice as this is the only chip that is still in stock at Digi-Key, the LTC4311. I am also confident that this chip is up to the task since Adafruit says it can do it even if its at 100kHz, I don't mind with the 100kHz clock.

The problem I'm having is I'm not sure how the IC works, typically the I2C extenders I used usually in between the line and either buffer/converts the signal.

This one seems to "hook up" into an I2C bus just like any I2C device. The question is, do I place this IC on both ends? Just like this?

enter image description here

Although the question is mainly focused on the LTC4311, if you can offer other alternatives of an I2C extender that can reach 30m I will be glad to hear it (Digi-Key must have them in stock)

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  • \$\begingroup\$ I have used P82B715 over 20m of multi-core (not twisted-pair) cable without difficulty, and I expect it would go much further with a lower transmission speed. \$\endgroup\$
    – user131342
    Commented Oct 5, 2021 at 20:32

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You will need to use pull-up resistors as normal. The LTC4311 senses the beginning of the rise in voltage that the pull-up resistor produces and shoots more current into the bus to reduce the rise time to less than the R-C line system would normally take. You should only need one LTC4311 (30m of CAT5 cable is ~2000pF, well within the driving capability of the chip). You can also see that they show you how to substitute the LTC1694, which is in plentiful stock.

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  • \$\begingroup\$ Can i parrelel multiple of these so that i can increase the speed/length? Also my i2c master has only 10mA drive? will it be allright? \$\endgroup\$
    – DrakeJest
    Commented Oct 5, 2021 at 20:52
  • \$\begingroup\$ Yes, page 10 states that you can put two in parallel to drive very heavily loaded lines though like I said, I doubt you'll need two. Couldn't hurt to drop in the footprint and not populate it. The drive current of the master is mostly irrelevant as the LTC4311 provides its own current to the bus. You can also try your luck with low capacitance cable (~12 pF/ft) but you should be fine with normal stuff for 30m. \$\endgroup\$
    – vir
    Commented Oct 5, 2021 at 20:57
  • \$\begingroup\$ _ Couldn't hurt to drop in the footprint and not populate it._ My thoughts exactly ! Then this is i think a good IC for me. Thank you very much! \$\endgroup\$
    – DrakeJest
    Commented Oct 5, 2021 at 21:04

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