Communication failure using PCA9615 Differential I2C Bus Extender

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ehabawni

Joined Dec 7, 2011
7
I have used PCA9615 differential I2C bus driver in one design to extend the I2C bus over CAT5 cable.
(datasheet https://www.nxp.com/docs/en/data-sheet/PCA9615.pdf)

The design has been done according to the datasheet recommendation and with the help of a reference design of a popular open-source board manufactured by Sparkfun which I used as a demo board, before starting the design.

Unfortunately, the design didn't work well in my case, as the communication doesn't establish when connecting a pair of PCA9615 using CAT5 cable.
I have attached my schematic and layout of the board, and the connection topology I used.
Here are some observations:
  • It seems when connecting the PCA9615 boards over the ethernet cable (tested it using 1 m long cable), both SDA and SCL lines get pulled low, so there is no connection over I2C.
  • The termination resistors have been calculated according to the datasheet recommendations (yielding 88.5Ohm parallel resistance close to the 100Ohm indicated in the datasheet, it should work since SparkFun's module uses the same values as I)
  • I tested it for the pin-to-pin continuity for one board to another and it's correct.
  • Every board is designed with three I2C inputs, if I connected to two I2C devices on the same board without connecting the second board, then it works fine, which means no problem from the I2C side.
  • I have tested the voltage levels on both boards and they indicate correct voltage levels (5V in my case)

I would appreciate any help or suggestion regarding this problem.
 

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