AAT4296/98
Five/Six Channel Push/Pull I/O Expander
Driving LED Loads
(VIN - VF)
RLED
=
- RDS(ON)
The AAT4296 and AAT4298 can be used to drive
LEDs or other applications with light load current
requirements. LED applications may include main
and sub-LCD display backlighting, camera photo-
flash applications, color (RGB) LEDs, and infrared
(IR) diodes for remotes. In series with LEDs, bal-
last resistors must be used to limit the LED current.
The LED current will vary with supply voltage and
LED forward voltage. Most types of LEDs have for-
ward voltage specifications ranging from 2.0V to
5.0V. Calculate the necessary ballast resistor value
from the following formula:
ILED
Where:
RLED is the resistance of resistor to be placed in
series with the LED (Ω).
VIN is the input supply voltage to the device (V).
VF is the forward voltage of the LED (V).
RDS(ON) is the resistance of the switch when it is
turned on (Ω).
ILED is the desired operating current of the LED (A).
5V
AAT4296
EN
EN
Bluetooth
Device
OUT1
OUT2
OUT3
OUT4
OUT5
OUT6
IN
Infrared
Device
A series of
pulses
EN/SET
GND
Backlighting
R
G
B
Figure 5: Infrared, Bluetooth, RGB, and Backlighting Control.
14
4296.2006.12.1.3
AAT [ ADVANCED ANALOG TECHNOLOGY, INC. ]
