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PCA9306: PCA9306 – Rref1 > Vref2 Question

Part Number: PCA9306

The circuit is designed in the figure below, we measured the value of Pin2 is 3.31V; the Pin7 is 3.25V. What effect will Vref1>Vref2 have on the device? 

BR, Gary

  • In theory, there should be no voltage difference. It looks as if there is a leakage current of 0.3 µA somewhere.

    Anyway, these voltages are OK; the PCA9306 will still work as an I²C switch. (The voltages will be clamped at EN − 0.8 V, but the pull-up resistors take care of that.)

  • One more question.

    If VREF1 = VREF2=3.3V and Ven reach 3.3V, it means that the Vgs voltage is ~0V, which will cause the switch can't turn-on. Is that correct?

    BR, Gary

  • When Vgs = 0 V, then the transistor indeed does not turn on.

    However, the figure shows only the reference transistor, which does not matter in this application. There are similar transistors between the other I/Os, and those switch on when the voltage at an I/O pin goes low.

    (In this figure, no DC current flows through the 200 kΩ resistor, so you can simply connect EN directly to the lowest power supply.)