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PCA9306: PCA9306 behaviour when one side is unpowered

Mat1980
Intellectual 1260 points
Part Number: PCA9306

Hello gents,

I am using 3.3V on side 1 and 5V on side 2. EN is connected through a pullup through on the 5V side.

Now my question is, what can happen if the 5V rail is powered up before the 3.3V?
Is there a chance that the device is harmed?

Thanks!
Matthias

  • 0
    TI__Guru 62920 points

    Hi Matthias,

    Just to confirm - you have both EN and VREF2 tied together and then pulled via a shared 200-kOhm resistance to your 5-V supply (as shown on the first page of the datasheet), correct?

    Assuming that is the case, having the 5-V side powered before the 3.3-V side will not stress the device or result in damage.  There are a couple of things to be aware of, though.  One is that since the SCL1/SDA1 signals will likely be low, the SCL2/SDA2 signals would be low as well.  This means I2C communication may not work until the 3.3-V rail is active.  Another thing to know is that there will be some leakage current flow from VREF2 to VREF1.  The magnitude of the leakage would be [VREF2 - (VREF1 + 0.6 V)] / Rpullup.  If the components on the VREF1 side do not sink this small current, you may observe a voltage rise on the VREF1 rail before the 3.3-V power supply is active.

    Regards,
    Max

  • 0 in reply to Miguel Robertson
    TI__Intellectual 1260 points

    thanks for the feedback Max!