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Original question:

TCA9509: I2C buffer Application

TCA9509: I2C buffer Application

R. E. Jozefzoon
Prodigy 120 points
Part Number: TCA9509
Other Parts Discussed in Thread: TCA9517

Hi,

I am using two TCA9509DGKR to disable/isolate two humidity I2C sensors. The A and B side of the TCA9509 are both running on 5V. I cannot seem to get any data from the B side, The A side is showing I2C data.

Removing the sensors as a test and changing the output resistors did not improve anything. 

Attached my schematic. Please give me your support.

Thank you,

Roy

  • 0
    TI__Guru 60540 points

    Hey Roy,

    I see two potential concerns with your schematic.

    1) TCA9509 wants VccB to be atleast 1 V larger than VccA

    2) Having two TCA9509 A sides connected together (assuming they are both enabled) could cause issues because they both use a current sensing/sourcing mechanism on A side to detect lows. Having both of them connect together could be causing the two to interfere with each other.

    Can you show me scope shots of SDA and SCL on A side?

    Can you remove one TCA9509 and see if communication works if one is removed?

    Are you sure the device is enabled when you are trying to communicate?

    Are there any pull up resistors on A side? (internal pull ups from your master?) This could also affect the current sensing/sourcing mechanism of the device.

    I believe TCA9517 would be a more suitable solution than TCA9509 because of the VccA=VccB rule. It is also pin to pin from what I can see so I also suggest you swap out the TCA9509 and TCA9517 (add pull up resistors on A side) and see if you are still seeing issues.

    Thanks,

    -Bobby

  • 0 in reply to BOBBY
    Prodigy 120 points

    Hi Bobby,

    Thanks for your very valuable response.

    I missed the part about Vccb having to be at least 1V or higher than Vcca. Too bad that this kind of important detailed is not given the importance it deserves, i.m.o..

    Maybe I should not use this part since Vcca ≤ (Vccb -1) and I only have 5V available on my board.

    It is a good thing that I can use a pin compatible device like your suggestion the TCA9517, this also saves me a board redesign. It also clearly states that I can use the TCA9517 in a star configuration (exactly how I want to use it).

    I will order a few of these parts and do some tests.

    side A has pull-ups resistors but are not installed (and shown in the schematic). When using the TCA9517 I will install them.

    Sorry for not answering your other questions but I just makes perfect sense to use the TCA9517.

    Thank you again,

    Regards,

    Roy