PCA9554DW Datasheet, PDF (23/36 Pages) Texas Instruments – REMOTE 8-BIT I2C AND SMBus I/O EXPANDER WITH INTERRUPT OUTPUT AND CONFIGURATION REGISTERS

Not Recommended for New Designs
PCA9554
www.ti.com ........................................................................................................................................................ SCPS128B – JULY 2006 – REVISED AUGUST 2008
Minimizing I_CC When I/Os Control LEDs
When the I/Os are used to control LEDs, they are normally connected to V_CC through a resistor as shown in
Figure 14. The LED acts as a diode, so when the LED is off, the I/O V_IN is about 1.2 V less than V_CC. ΔI_CC in
Electrical Characteristics shows how I_CC increases as V_IN becomes lower than V_CC.
For battery-powered applications, it is essential that the voltage of I/O pins is greater than or equal to V_CC when
the LED is off to minimize current consumption. Figure 15 shows a high-value resistor in parallel with the LED.
Figure 16 shows V_CC less than the LED supply voltage by at least 1.2 V. Both of these methods maintain the I/O
V_IN at or above V_CC and prevent additional supply-current consumption when the LED is off.
V_CC
V_CC
LEDx
LED 100 kW
Figure 15. High-Value Resistor in Parallel With LED
3.3 V
5V
V_CC
LED
LEDx
Figure 16. Device Supplied by a Lower Voltage
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