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TCA9617A: SDA on A side is driven/pulled low

David Guest1
Intellectual 350 points
Part Number: TCA9617A
Other Parts Discussed in Thread: TCA9803, TCA9617B

We have one of these buffers to drive external peripherals off-board.

The A side is connected to the CPU and is running at 3.3V.  The B side supply is currently 0V (off), so we are confused why the SDA pin is pulled/driven low (SCL pin is ok)

We have a 10K pull-up on the pcb - which as its a low power design and compact works well (works perfectly when buffer is removed from pcb)

Any ideas ?

  • 0
    Guru 317260 points

    Section 10 of the datasheet says:

    VCCB cannot be lower than VCCA even when the device is disabled.

    The TCA9617B does not have this restriction, but the datasheet does not say anything about what happens when one supply is off. The TCA9803 has a defined behaviour in this case.

  • 0
    TI__Guru 73591 points

    As Clemen's pointed out, the A version of TCA9617 has an issue where if A side powers up before B side, there will be leakage current into B side which could turn the device on and could drive B side to lock A low. This was resolved/fixed in the B version of the TCA9617 which we recommend customers move to if they are power sequencing A before B.

    -Bobby