AATIAN78 Datasheet, PDF (1/4 Pages) SiGe Semiconductor, Inc. – Triple I/O Expander Load Switch with Serial Control

EV-101
AAT4291 RGB EVAL
Triple I/O Expander Load Switch with Serial Control
Introduction
This document discusses the AAT4291 RGB EVAL
evaluation board and the application of the AAT4291
as an RGB LED driver. Advanced RGB LED control
is realized without having to use multiple discrete
MOSFET switches controlled by multiple I/O pins
from the system processor. Only one digital I/O pin
is needed for complete, independent brightness
control of each of the R, G, and B LEDs.
The AAT4291 SmartSwitch™ is a member of
AnalogicTech’s Application Specific Power MOS-
FET™ (ASPM™) product family. The AAT4291 has
three P-channel MOSFETs configured for use as a
microprocessor I/O expander. Having independent
drain outputs and a common input, the AAT4291
operates with an input voltage ranging from 1.8V to
5.5V, making it ideal for 2.5V, 3.3V, or 5V systems,
as well as systems powered by lithium-ion/polymer
batteries. Each switch features a fast 500ns turn-
SmartSwitch^™
on time. The switch states are controlled by the
Simple Serial Control™ (S²Cwire™) serial digital
interface. The quiescent supply current is very low,
typically 5µA. In shutdown mode, the supply cur-
rent is reduced to less than 1µA.
Using RGB LEDs to generate various colors pres-
ents unique challenges. Among them is a require-
ment to pulse width modulate (PWM) three inde-
pendent LED currents to accurately control the
brightness for each LED color. The AAT4291 is well
suited for this. Using only one GPIO pin from the sys-
tem processor, a high PWM rate can be achieved
with complete brightness control for each LED.
The following material describes the hardware and
software platform used to generate many colors of
light from RGB LEDs. In addition to this literature,
the reader is encouraged to also consult the
AAT4290/4291 product datasheet.
Schematic
C2
10µF
U1
1
2
VOUT
GND
3 _GND
4 _GND
C+ ⁸
VIN
C-
7
6
SHDN ⁵
AAT3110-4.5
VIN
J1
VIN
2
1
GND
R6
100K
C1
10µF
VIN
C3
1µF
U2
1 _IN
OUT3 ⁸
2 _NC
OUT2 ⁷
3 _NC
OUT1 ⁶
4 _{EN/SET GND} 5
ATT4291
C4
VIN 10µF
C6
0.1µF
S1
S2
S3
S4
S5
R1 R2 R3 R4 R5
1K 1K 1K 1K 1K
U3
1 _VDD
2 _GP5
3 _GP4
4 _GP3
VSS ⁸
GP0 ⁷
GP1 ⁶
GP2 ⁵
PIC12C671
R9
R8
R7
60.4
249
249
4
3
2
D1R
RED
1615 SMD
D1G
GREEN
1
D1B
BLUE
R10
R11
R12
60.4
249
249
2
3
4
D2R
RED
1615 SMD
D2G
GREEN
1
D2B
BLUE
Figure 1: Evaluation Board Schematic.
EV-101.2005.01.1.0
1