TCA9554_15 Datasheet, PDF (23/38 Pages) Texas Instruments – TCA9554 Low Voltage 8-Bit I2C and SMBus Low-Power I/O Expander With Interrupt Output and Configuration Registers

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TCA9554
SCPS233D – MARCH 2012 – REVISED AUGUST 2015
Typical Application (continued)
9.2.1 Design Requirements
9.2.1.1 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 24. For a P-port configured as an input, I_CC increases as V_I becomes lower than V_CC. The LED is a diode,
with threshold voltage V_T, and when a P-port is configured as an input the LED will be off but V_I is a V_T drop
below V_CC.
For battery-powered applications, it is essential that the voltage of P-ports controlling LEDs is greater than or
equal to V_CC when the P-ports are configured as input to minimize current consumption. Figure 25 shows a high-
value resistor in parallel with the LED. Figure 26 shows V_CC less than the LED supply voltage by at least V_T.
Both of these methods maintain the I/O V_I at or above V_CC and prevents additional supply current consumption
when the P-port is configured as an input and the LED is off.
V_CC
V_CC
LEDx
LED 100 kW
Figure 25. High-Value Resistor in Parallel With LED
3.3 V
5V
V_CC
LED
LEDx
Figure 26. Device Supplied by a Lower Voltage
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