ZHCS616E March 2012 – February 2017 TCA9554
PRODUCTION DATA.
When an I/O is configured as an input, FETs Q1 and Q2 are off, creating a high-impedance input with a weak pull-up (100 kΩ typical) to VCC. The input voltage may be raised above VCC to a maximum of 5.5 V, however it must be noted that because of the integrated 100 kΩ pull-up resistor it may result in current flow from I/O to VCC pin (Figure 15).
If the I/O is configured as an output, Q1 or Q2 is enabled depending on the state of the output port register. In this case, there are low impedance paths between the I/O pin and either VCC or GND. The external voltage applied to this I/O pin must not exceed the recommended levels for proper operation.