TCA6424_10 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
SCPS175A – NOVEMBER 2007 – REVISED NOVEMBER 2009
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
Power-On Reset Requirements
In the event of a glitch or data corruption, TCA6424 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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