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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 SmartSwitchTM is a member of AnalogicTech's Application Specific Power MOSFETTM (ASPMTM) 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-
SmartSwitchTM
on time. The switch states are controlled by the Simple Serial ControlTM (S2CwireTM) serial digital interface. The quiescent supply current is very low, typically 5A. In shutdown mode, the supply current is reduced to less than 1A. 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 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 3 4
C2 10F
VOUT C+ GND VIN GND CGND SHDN AAT3110-4.5
8 7 6 5
C3 1F U2
1 2
R6 VIN J1 VIN GND
2 1
3 4
100K C1 10F
IN OUT3 NC OUT2 OUT1 NC EN/SET GND ATT4291
8 7 6 5
R9 60.4 VIN C4 10F
4
R8 249
R7 249
R10 60.4
R11 249
R12 249
VIN
3
2
2
3
4
C6 0.1F
U3 R1 1K R2 1K R3 1K R4 1K R5 1K
1 2 3 4
S1 S2 S3 S4 S5
VDD GP5 GP4 GP3 PIC12C671
VSS GP0 GP1 GP2
8 7 6 5
D1R RED 1 1615 SMD
D1G GREEN
D1B BLUE
D2R RED
D2G GREEN 1
D2B BLUE
1615 SMD
Figure 1: Evaluation Board Schematic.
EV-101.2005.01.1.0
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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 1s (see Figure 1). THI and TLO depend on the C's internal RC oscillator, so the 1s 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
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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#
AAT3110 AAT4291 PIC12C671 1615 SMD GRM31CR70J106KA01L ECJ-1VB1A105K ECJ-1VB1C104K Chip Resistor Chip Resistor Chip Resistor Chip Resistor Chip Resistor PTS645TL50
Description
Power Regulated 4.5V CP; SC70JW-8 Package I/O Expander Load Switches; SC70JW-8 Package 8-Bit CMOSC; 8-Pin PDIP Package RGB LED, Common-Cathode; 1615 SMD 10F, 6.3V, X7R, 10%; 1206 1F, 10V, X5R, 10%; 0603 0.1F, 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
Manufacturer
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

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