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PCA9518: PCA9518

eli
Guru 13485 points
Part Number: PCA9518

In my customer  design,he  is connected to another OEM board as described below.

The I2C coming from the OEM board is expanded using PCA9518 device on my board.

Is there any issue with this connection?

  • 0
    TI__Guru 62920 points
    Hi Eli,

    No, it is not possible to connect multiple PCA9518 devices in series like this. The output low level is intentionally set to be higher than the input low level of this device (to support bidirectional communication without requiring a direction control signal), which means that low signals output from one device may not be recognized by another device sharing the same port.

    It is possible to use the EXPx pins to connect two of these buffers together to allow for higher port counts. Figure 3 in the datasheet gives an example implementation.

    Best regards,
    Max
  • 0 in reply to Miguel Robertson
    Guru 13485 points

    Hi Max

    The OEM board cannot be changed, what do you suggest me to do? I need to use USB HUB on my design.

    Attached is the OEM AN on that issue,

    Base on the AN do you think using  PCA9512 between PAC9518 will solve the issue?CTN 20150526 001.pdf

  • 0 in reply to eli
    TI__Guru 60850 points
    Hey Eli,

    "Base on the AN do you think using PCA9512 between PAC9518 will solve the issue?"
    -That device is not a TI device so I am unfamiliar with it. Based on the first page of the datasheet of the PCA9512 though I would say no because it runs into the same problem our buffered devices have. Buffered offset sides cannot be connected to each other. I also don't think that app note you referenced states what the devices are actually connected to (like another PCA9518 for example like you are doing).

    The only way I see this working correctly without contention problems is if you connect the EXPx pins together from your design to the OEM board (solder some jumper cables). Adding a buffer between the two like what that app note suggests will only work in one direction of communication and be prone to contention problems in the other direction.

    Thanks,
    -Bobby