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PCA9306: Voltage on SCL/SDA while device unpowered

Matthew Handley
Prodigy 10 points
Part Number: PCA9306


Hello,

I am planning to use the PCA9306DCTR to isolate several slaves on an I2C bus where the slaves are not always powered, but the master is. The master and it's pull-ups are on a different board with it's own 3.3V supply, which I do not easily have access to. I plan to power both VREF1 and VREF2 from the slave's 3.3V bus, which is sometimes off.

My question is this: Are there any problems with the SDA1 and SCL1 pins being pulled high by the master while both the VREF pins are at 0V? Will the voltage from the SCL1 and SDA1 pins leak onto any other pin? Can this damage the device?

Thanks,

Matt

  • 0
    TI__Guru* 75391 points
    Hey Matt,

    "Are there any problems with the SDA1 and SCL1 pins being pulled high by the master while both the VREF pins are at 0V?"
    If the Vref pins and enable pin are GND (0V) then side 1 and side 2 of the device are high impedance (think of it as open switch between the two sides).

    "Will the voltage from the SCL1 and SDA1 pins leak onto any other pin? "
    No, not in the steady state analysis anyways (maybe some nanoamp current range if we wanna be super technical). In the AC sense, fast rise times could result in cross talk into the enable pin though to be honest this is very unlikely and if you have a small capacitor on the enable pin (100pF) it would help to minimize the effect. In my opinion, you shouldn't see any issues.

    "Can this damage the device?"
    If you are keeping the voltage 5V or lower (even when powered off) then this will not damage the device.

    Thanks,
    -Bobby