TCA6424 Datasheet, PDF (24/29 Pages) Texas Instruments – LOW-VOLTAGE 24-BIT I2C AND SMBus I/O EXPANDER WITH INTERRUPT OUTPUT, RESET, AND CONFIGURATION REGISTERS

TCA6424
LOW-VOLTAGE 24-BIT I²C AND SMBus I/O EXPANDER
WITH INTERRUPT OUTPUT, RESET, AND CONFIGURATION REGISTERS
SCPS175 – NOVEMBER 2007
www.ti.com
Minimizing I_CC When I/Os Control LEDs
When the I/Os are used to control LEDs, normally they are 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. The ΔI_CC
parameter in Electrical Characteristics shows how I_CC increases as V_IN becomes lower than V_CC. Designs that
must minimize current consumption, such as battery power applications, should consider maintaining the I/O pins
greater than or equal to V_CC when the LED is off.
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
Px
LED
100 kW
Figure 15. High-Value Resistor in Parallel With the LED
3.3 V
5V
V
CC
Px
LED
Figure 16. Device Supplied by a Low Voltage
24
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