TCA9555 Datasheet, PDF (23/32 Pages) Texas Instruments – LOW VOLTAGE 16-BIT I2C AND SMBus I/O EXPANDER WITH INTERRUPT OUTPUT AND CONFIGURATION REGISTERS

TCA9555
www.ti.com .............................................................................................................................................................. SCPS200A – JULY 2009 – REVISED JULY 2009
Minimizing I_CC When I/O Is Used to Control LED
When an I/O is used to control an LED, normally it is connected to V_CC through a resistor as shown in Figure 15.
Because the LED acts as a diode, 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. 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 16 shows a high-value resistor in parallel with the LED. Figure 17 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
Pn
LED
100 kW
Figure 16. High-Value Resistor in Parallel With LED
3.3 V
5V
V_CC
Pn
LED
Figure 17. Device Supplied by Lower Voltage
Power-On Reset Requirements
In the event of a glitch or data corruption, TCA9555 can be reset to its default conditions by using the power-on
reset feature. Power-on reset requires that the device go through a power cycle to be completely reset. This
reset also happens when the device is powered on for the first time in an application.
The two types of power-on reset are shown in Figure 18 and Figure 19.
V_CC
Ramp-Up
Ramp-Down
Re-Ramp-Up
V_{CC_TRR_GND}
V_{CC_RT}
V_{CC_FT}
Time to Re-Ramp
V_{CC_RT}
Figure 18. V_CC is Lowered Below 0.2 V or 0 V and Then Ramped Up to V_CC
Time
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