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Minimizing I

CC When the I/O is Used to Control LEDs

LED

100 k

Ω

3.3 V

LED

5 V

TCA6408

LOW-VOLTAGE 8-BIT I2C AND SMBus I/O EXPANDER

WITH INTERRUPT OUTPUT, RESET, AND CONFIGURATION REGISTERS

SCPS151C – FEBRUARY 2007 – REVISED JUNE 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. The ∆ICC

parameter in "Electrical Characteristics" shows how ICC increases as VIN becomes lower than VCC. Designs

needing to minimize current consumption, such as battery power applications, should consider maintaining the

I/O pins greater than or equal to VCC when the LED is off.

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 prevent additional

supply current consumption when the LED is off.

Figure 15. High-Value Resistor in Parallel With the LED

Figure 16. Device Supplied by a Low Voltage

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