Datasheet

LED
LEDx
V
CC
100 kW
V
CC
LED
3.3 V
5 V
LEDx
V
CC
V
CC
Ramp-Up Re-Ramp-Up
Time to Re-Ramp
Time
Ramp-Down
V
CC_RT
V
CC_RT
V
CC_FT
V
CC_TRR_GND
TCA9554
SCPS233A –NOVEMBER 2011–REVISED MARCH 2012 www.ti.com
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 16. 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 17 shows a high-value resistor in parallel with the LED.
Figure 18 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.
Figure 17. High-Value Resistor in Parallel With the LED
Figure 18. Device Supplied by a Lower Voltage
Power-On Reset Requirements
In the event of a glitch or data corruption, TCA9554 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 19 and Figure 20.
Figure 19. V
CC
is Lowered Below 0.2 V or 0 V and Then Ramped Up to V
CC
22 Submit Documentation Feedback Copyright © 2011–2012, Texas Instruments Incorporated
Product Folder Link(s): TCA9554