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PCA9306: Questions about the two VREF

Silvia Gao
Prodigy 170 points
Part Number: PCA9306


Hi team,

For "PCA9306DCUR", VREF1 is connected to "P3V3_STBY", VREF2 is connected to "P3V3" (main power supply) as the figure below. There is no voltage difference between VREF1 and VREF2.

I am wondering does the "PCA9306DCUR" operate in a proper condition under this connection?

Best Regards

Silvia Gao

  • +1
    Guru 318050 points

    When the difference between the two reference voltages is too small, then the clamping voltage is slightly below VREF1, and the maximum speed is somewhat lower. For a slow protocol like I²C, this does not matter.

  • +1
    TI__Guru 51398 points

    HI Silvia,

    This implementation should work properly since you are not using the device as a level translator. 3.3V from two different power supplies on VREF1 and VREF2 should work. If customer decides to use the device as a level translator (say 1.8V to 3.3V), this would not work in the current setup. 

    Clemens comment is also correct. He is touching on the threshold voltage of the internal passFET. The output side will not see an input LOW signal until the input voltage falls below 3.3V - Vth = ~ 2.7V since the threshold voltage of the internal passFET can be estimated to be 0.6V. At I2C speeds <1MHz, this should not be a problem since the hang time is effect from this threshold voltage is on the scale of nanoseconds. 

    Regards,

    Tyler