SCPS128D July 2006 – March 2021 PCA9554
When the I/Os are used to control LEDs, they are normally connected to VCC through a resistor as shown in Figure 9-1. The LED acts as a diode, so when the LED is off, the I/O VIN is about 1.2 V less than VCC. ΔICC in Electrical Characteristics shows how ICC increases as VIN becomes lower than VCC.
For battery-powered applications, it is essential that the voltage of I/O pins is greater than or equal to VCC when the LED is off to minimize current consumption. Figure 9-2 shows a high-value resistor in parallel with the LED. Figure 9-3 shows VCC less than the LED supply voltage by at least 1.2 V. Both of these methods maintain the I/O VIN at or above VCC and prevent additional supply-current consumption when the LED is off.