PCA9554ADGVR datasheet(23/33 Pages) TI

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Minimizing I

CC When I/Os Control LEDs

LED

LEDx

VCC

100 kW

VCC

LED

3.3 V

5 V

LEDx

VCC

PCA9554A

REMOTE 8-BIT I2C AND SMBus I/O EXPANDER

WITH INTERRUPT OUTPUT AND CONFIGURATION REGISTERS

SCPS127A – SEPTEMBER 2006 – REVISED FEBRUARY 2007

APPLICATION INFORMATION (continued)

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

Figure 14. The LED acts as a diode so when the LED is off the I/O VIN is about 1.2 V less than VCC. ∆ICC 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 15 shows a high value resistor in parallel with the LED.

Figure 16 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.

Figure 15. High-Value Resistor in Parallel With LED

Figure 16. Device Supplied by a Lower Voltage

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