AATI_AN_78.pdf

EV-101
AAT4291 RGB EVAL
Triple I/O Expander Load Switch with Serial Control
SmartSwitch™
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.
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 current is reduced to less than 1µA.
Using RGB LEDs to generate various colors presents unique challenges. Among them is a requirement to pulse width modulate (PWM) three independent 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 system processor, a high PWM rate can be achieved
with complete brightness control for each LED.
The AAT4291 SmartSwitch™ is a member of
AnalogicTech’s Application Specific Power MOSFET™ (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-
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
U1
1
2
C2
10µF
3
4
VOUT
C+
GND
VIN
GND
CGND SHDN
8
7
C3
1µF
6
5
U2
1
AAT3110-4.5
2
R6
VIN
GND
4
100K
J1
VIN
3
1
8
7
6
5
ATT4291
C1
10µF
2
IN
OUT3
NC
OUT2
OUT1
NC
EN/SET GND
R9
60.4
VIN
VIN
4
C6
0.1µF
R8
249
R7
249
R10
60.4
R11
249
R12
249
2
3
4
D2R
RED
D2G
GREEN
D2B
BLUE
C4
10µF
3
2
U3
R1
1K
R2
1K
R3
1K
R4
1K
R5
1K
1
2
3
4
S1
VDD
GP5
GP4
GP3
PIC12C671
VSS
GP0
GP1
GP2
8
7
6
5
D1R
RED
D1G
GREEN
D1B
BLUE
1
1615 SMD
1
1615 SMD
S2
S3
S4
S5
Figure 1: Evaluation Board Schematic.
EV-101.2005.01.1.0
1
EV-101
AAT4291 RGB EVAL
Triple I/O Expander Load Switch with Serial Control
Getting Started
The evaluation board comes with a battery pack
attached. In this configuration, VIN is supplied from
three standard “AAA” alkaline batteries. Under new
conditions for the batteries, the input voltage is generally 4.7V ~ 4.8V and falls off depending on the
degree of discharge and load conditions. If desired,
the batteries can be removed and an independent,
DC supply can be used.
There are five buttons on the board. Their functions
are as follows:
•
•
•
•
•
SW1: Increments through the eight Output Setting states (Table 2 in the product datasheet).
SW2: Increments B_LED duty cycle.
SW3: Increments G_LED duty cycle.
SW4: Increments R_LED duty cycle.
SW5: Brings EN/SET low (shuts down the
AAT4291 device).
Notes:
1. Buttons 1 through 4 will automatically increment if held down.
2. Buttons 2 through 4 are set up so that a user
can independently control the corresponding
R, G, or B LED brightness. This is done by
incrementing the PWM duty cycle through the
following states: 0%, 25%, 50%, 75%, 100%,
0%, …
The PIC microcontroller toggles the EN/SET line
high and low at 500kHz. The rise and fall times of
the EN/SET signal are small relative to the period,
so THI and TLO are roughly 1µs (see Figure 1). THI
and TLO depend on the µC's internal RC oscillator,
so the 1µs reference is an approximate figure and
subject to the precision of the RC oscillator.
Figure 2: Typical EN/SET Signal.
2
EV-101.2005.01.1.0
EV-101
AAT4291 RGB EVAL
Triple I/O Expander Load Switch with Serial Control
Printed Circuit Board
Figure 3: Top Layer Silkscreen (not to scale).
Figure 4: Top Layer (not to scale).
Figure 5: Bottom Layer (not to scale).
EV-101.2005.01.1.0
3
EV-101
AAT4291 RGB EVAL
Triple I/O Expander Load Switch with Serial Control
AAT4291 EVAL-RGB Component Listing
Component
U1
U2
U3
OP1, OP2
C1, C2, C4
C3
C6
R1 - R5
R6
R7, R12
R8, R11
R9, R10
SW1 - SW5
Part#
Description
Manufacturer
AAT3110
AAT4291
PIC12C671
1615 SMD
GRM31CR70J106KA01L
ECJ-1VB1A105K
ECJ-1VB1C104K
Chip Resistor
Chip Resistor
Chip Resistor
Chip Resistor
Chip Resistor
PTS645TL50
µPower Regulated 4.5V CP; SC70JW-8 Package
I/O Expander Load Switches; SC70JW-8 Package
8-Bit CMOSµC; 8-Pin PDIP Package
RGB LED, Common-Cathode; 1615 SMD
10µF, 6.3V, X7R, 10%; 1206
1µF, 10V, X5R, 10%; 0603
0.1µF, 16V, X7R, 10%; 0603
1K, 5%, 1/8W; 0805
100K, 5%, 1/10W; 0603
249, 1%, 1/10W; 0805
249, 1%, 1/10W; 0805
60.4, 1%, 1/10W; 0805
Switch Tact, SPST, 5mm
AnalogicTech
AnalogicTech
Microchip
Lasemtech
Murata
Panasonic-ECG
Panasonic-ECG
Vishay
Vishay
Vishay
Vishay
Vishay
ITT Industries
AnalogicTech cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in an AnalogicTech product. No circuit patent licenses, copyrights, mask work
rights, or other intellectual property rights are implied.
AnalogicTech reserves the right to make changes to their products or specifications or to discontinue any product or service without notice, and advise customers to obtain the latest
version of relevant information to verify, before placing orders, that information being relied on is current and complete. All products are sold subject to the terms and conditions of sale
supplied at the time of order acknowledgement, including those pertaining to warranty, patent infringement, and limitation of liability.
AnalogicTech warrants performance of its semiconductor products to the specifications applicable at the time of sale in accordance with AnalogicTech’s standard warranty. Testing and
other quality control techniques are utilized to the extent AnalogicTech deems necessary to support this warranty. Specific testing of all parameters of each device is not necessarily
performed.
Advanced Analogic Technologies, Inc.
830 E. Arques Avenue, Sunnyvale, CA 94085
Phone (408) 737-4600
Fax (408) 737-4611
4
EV-101.2005.01.1.0
Similar pages