TCA9554A Datasheet, PDF (25/33 Pages) Texas Instruments – LOW VOLTAGE 8-BIT I2C AND SMBus I/O EXPANDER

TCA9554A
www.ti.com
SCPS196 – DECEMBER 2010
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. 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
supply current, I_CC, increases as V_IN becomes lower than V_CC and is specified as ΔI_CC in Electrical
Characteristics.
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 prevents 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 the LED
3.3 V
5V
V_CC
LED
LEDx
Figure 16. Device Supplied by a Lower Voltage
Power-On Reset Requirements
In the event of a glitch or data corruption, TCA9554A 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 17 and Figure 18.
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}
Time
Figure 17. V_CC is Lowered Below 0.2 V or 0 V and Then Ramped Up to V_CC
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