Datasheet

Minimizing I
CC
When I/O Is Used to Control LED
LED
100 kW
V
CC
V
CC
Pn
3.3 V
LED
5 V
V
CC
Pn
PCA9557
www.ti.com .................................................................................................................................................... SCPS133I – DECEMBER 2005 – REVISED JUNE 2008
When an I/O is used to control an LED, normally it is 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 Δ I
CC
parameter in
Electrical Characteristics shows how I
CC
increases as V
IN
becomes lower than V
CC
. Designs needing to 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.
Figure 15. High-Value Resistor in Parallel With the LED
Figure 16. Device Supplied by a Low Voltage
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