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TCA9801: I2C Issues using I2C Buffer TCA9801+TCA9617

Nicolai Adelhoefer
Prodigy 30 points
Part Number: TCA9801
Other Parts Discussed in Thread: TCA9617B, TCA9509

Hey,
actually I have some issues with the I2C bus using ti components. I have connected the TCA9801->B and TCA9617->B Side. I have some undershooting issues which may be resolved by a series resistance. But there is also some kind of square wave on scl + sda when bus is pulled low.... this is alternating so high(up to 0.58V which is > 0.4V) that it causes errors on the i2c, the slaves don't acknoledge. I have read the datasheets + recommendations but I didnt come to a solution.

When connecting both sides to other i2c debugging tool or master/slaves they work good, so there might be some issue with TCA9801->B and TCA9617->B. But considering the datasheets it shall be okay if I understood everything correctly...

Maybe you have some idea ... Thanks for your help!

  • 0
    Guru 299120 points

    The TCA9617B uses a static voltage offset on the B side. Section 10.1.2.2 of the TCA9801 datasheet says this cannot be used with its B side.

  • 0 in reply to Clemens Ladisch
    Prodigy 30 points

    Hey,

    thank you a lot for the quick response! Well you are definitly right, I must have overseen the section. I found another chip, the TCA9509 wich is pin compatible to the TCA9801 but has the current sources at the A side, what would fit my design as well. Do you think a connection of TCA9509->B to TCA9617->B can work?

  • 0 in reply to Nicolai Adelhoefer
    TI__Guru 63720 points

    Hi Nicolai,

    That kind of set up an work. I should point out that TCA9509 was designed such that VccB should be larger than VccA by atleast 1V otherwise you may see some differences in the electrical characteristics.

    -Bobby