Datasheet

Minimizing I
CC
When I/Os Control LEDs
LED
LEDx
V
CC
100 kW
V
CC
LED
3.3 V
5 V
LEDx
V
CC
PCA9538
www.ti.com ................................................................................................................................................ SCPS126E – SEPTEMBER 2006 – REVISED JUNE 2008
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
. I
CC
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 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.
Figure 15. High-Value Resistor in Parallel With LED
Figure 16. Device Supplied by a Lower Voltage
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