PCA9557: about PCA9557 I/O impedance

Hey Vera,

The answer really depends:

1) If the ports are all set as inputs, then all the pins would be high impedance.

2) If all the ports are outputs, the pins with a push pull design should always be applying a bias voltage (0V or Vcc) at the gate and turning on a FET (p or n) resulting in a low impedance path on the output. With P0, the design is an open drain. With 0V applied on the gate, the FET will not be turned on and will act as high impedance. However if Vcc is applied to the gate, the FET will turn on as a low impedance path to ground.

You can see a simplified internal schematic on the datasheet on pages 13 and 14. (Figures 17 and 18)

Thanks,

-Bobby