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TCA9406: VCCA to get HiZ on ports

Michael Jensen
Intellectual 485 points
Part Number: TCA9406
Other Parts Discussed in Thread: PCA9306, TCA9517

I am using the TCA9406 to separate TM4C1290 from longer lines to battery driven devices. 3V3 is connected to TM4C1290 and TCA9406 VCCA and OE. VCCB is always powered.

When the 3V3 is shut off, it falls to below 0,8V, will the TCA9406 then go into HiZ? Or at what voltage can that be expected?

/Michael

  • 0
    TI__Guru 72751 points

    Hey Michael,

    I would suggest you pull the OE to below 0.6V to ensure the device goes into Hi-Z.

    What voltage is VCCB and what is the max frequency you expect to be using? If this voltage (on OE) is too low for you to obtain, I can see if I can find you a different solution.

    Thanks,

    -Bobby

  • 0 in reply to BOBBY
    Intellectual 485 points

    Hi Bobby,

    datasheet says Vil for OE to be VCCAx0,35 but since VCCA is falling at the same time, I can only rely on VCCA to get into HiZ. Or?

    The question was at what voltage will the VCCA turn it into HiZ? The datasheet says 0V but that is actual very hard to get precisely, so I expect something like below 1,5V or similar but I can't find it in the datasheet.

    VCCB is 3,5V - 4,2V and frequency is up to 400K.

    /Michael

  • 0 in reply to Michael Jensen
    TI__Guru 72751 points
    Hey Michael,

    My original response assumed that the internals of the TCA9406 was similar to PCA9306 where EN would need to be below 0.6V to make the device Hi-Z. I spoke with our senior engineer and it looks like the datasheet's VccAx0.35 is actually the correct value for the enable ViL voltage. This means you would see the device go into the HI-Z once VccA falls below around 1.2V (because it is tied to EN).

    It seems like your question is if VCCA drops below a certain voltage, will it go into Hi-Z and if so what voltage (independent of the EN pin). A quick guess is that it will be around 800mV (similar to TCA9517).... In this case, it does not state in the datasheet and I will likely have to try to get a set up in the lab to verify this. I likely won't be able to get this information for you until either Monday or Tuesday of next week.

    Thanks,
    -Bobby
  • 0 in reply to BOBBY
    Intellectual 485 points
    Hi,
    and thanks for the info!

    It seems that I can derive a signal to control OE instead of relying on a low VCCA and that will probably be implemented. Better safe than sorry.

    /Michael