Datasheet

Minimizing I
CC
When I/O Is Used to Control LED
V
CC
V
CC
LED
Pn
100 kW
V
CC
3.3 V 5 V
LED
Pn
PCA9535
SCPS129I – AUGUST 2005 – REVISED MAY 2008 ........................................................................................................................................................... www.ti.com
When an I/O is used to control an LED, normally it is connected to V
CC
through a resistor as shown in Figure 15 .
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 Δ I
CC
parameter 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 16 shows a high-value resistor in parallel with the LED. Figure 17 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 16. High-Value Resistor in Parallel With LED
Figure 17. Device Supplied by Lower Voltage
22 Submit Documentation Feedback Copyright © 2005 – 2008, Texas Instruments Incorporated
Product Folder Link(s): PCA9535