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Minimizing ICC When I/O Is Used to Control LED

LED

100 kW

VCC

3.3 V

LED

5 V

VCC

PCA9557

www.ti.com.................................................................................................................................................... SCPS133I – DECEMBER 2005 – REVISED JUNE 2008

When an I/O is used to control an LED, normally it is 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 ΔICC 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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