PCA9555
REMOTE 16-BIT I2C AND SMBus I/O EXPANDER
WITH INTERRUPT OUTPUT AND CONFIGURATION REGISTERS
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SCPS131D–AUGUST 2005–REVISED OCTOBER 2006
APPLICATION INFORMATION (continued)
Minimizing ICC When I/O Is Used to Control LED
When an I/O is used to control an LED, normally it is connected to VCC through a resistor as shown in Figure 15.
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 ∆ICC
parameter 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 16 shows a high-value resistor in parallel with the LED. Figure 17 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.
V
CC
LED
100 kW
V
CC
Pn
Figure 16. High-Value Resistor in Parallel With LED
3.3 V
5 V
V
CC
LED
Pn
Figure 17. Device Supplied by Lower Voltage
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