9.1.1.1 Detailed Design Procedure

9.1.1.1.1 Minimizing ICC When I/Os Control Leds

When the I/Os are used to control LEDs, they are normally connected to VCC through a resistor as shown

in Figure 9-1. Because the LED acts as a diode, when the LED is off, the I/O VIN is about 1.2 V less than

VCC. The supply current, ICC, increases as VIN becomes lower than VCC and is specified as ΔICC in Electrical

Characteristics.

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 prevents additional supply-current consumption when the LED is off.

LED

LEDx

VCC

100 kW

VCC

Figure 9-2. High-Value Resistor In Parallel With The Led

LED

3.3 V

5 V

LEDx

VCC

Figure 9-3. Device Supplied By A Lower Voltage

PCA9554A

SCPS127F – SEPTEMBER 2006 – REVISED MARCH 2021

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