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ANALOGICTECH
ANALOGICTECH

EV-101 Datasheet Preview

EV-101 Datasheet

Triple I/O Expander Load Switch

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EV-101 pdf
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.
www.DataSheet4U.com
Schematic
C2
10µF
U1
1
2
VOUT
GND
3 GND
4 GND
C+ 8
VIN
C-
7
6
SHDN 5
AAT3110-4.5
J1
VIN
GND
2
1
VIN
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
60.4 249
R7
249
432
D1R
RED
1615 SMD
D1G
GREEN
1
D1B
BLUE
R10 R11
60.4 249
R12
249
234
D2R
RED
1615 SMD
D2G
GREEN
1
D2B
BLUE
EV-101.2005.01.1.0
Figure 1: Evaluation Board Schematic.
1



ANALOGICTECH
ANALOGICTECH

EV-101 Datasheet Preview

EV-101 Datasheet

Triple I/O Expander Load Switch

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EV-101 pdf
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 gen-
erally 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 Set-
ting 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 incre-
ment 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


Part Number EV-101
Description Triple I/O Expander Load Switch
Maker ANALOGICTECH
Total Page 4 Pages
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