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EV-130
AAT1231 EVAL: Step-Up DC/DC Converter
for White LED Backlight Applications
Introduction
The AAT1231 is a high frequency, high efficiency constant current boost converter driving up to six white LEDs
in series or up to twelve white LEDs in parallel/series configuration. The input voltage is 2.7V to 5.5V, which
is ideal for portable devices powered by single-cell lithium-ion/polymer (Li-ion) batteries. With over-voltage protection and dynamically-programmable voltage control via AnalogicTech’s patented Simple Serial Control™
(S2Cwire™) interface, the AAT1231 is an ideal choice for white LED backlight applications.
The AAT1231 evaluation board provides a platform for test and evaluation of the AAT1231 for white LED backlight applications driving six LEDs. The AAT1231 is programmable with the S2Cwire interface, using an
onboard microcontroller which is capable of brightening and dimming the LEDs in 26 discrete steps. The
SELECT logic signal from the microcontroller provides a stepped load from 1.5x to 3.0x of nominal output current, depending on the S2Cwire data register (default = 3.0x).
This document describes the evaluation board and its accompanying user interface. In addition, a brief
"Getting Started" section is included to help the user begin operating the evaluation board. A schematic of the
complete circuit is shown in Figure 1. The board layout is also provided. For additional information, please
refer to the AAT1231 product datasheet.
Schematic
VCC
R7
1K
R8
330
R6
1K
R5
1K
1
02
4
Up
D7
RED
02
4
Down
Select
02
4
1
3
5
1
3
5
1
3
5
C3
1µF
U2
SW3
2
3
4
SW2
VDD
GP5
GP4
GP3
VSS
GP0
GP1
GP2
8
7
6
R9
330
5
PIC12F675
D8
GREEN
(Select indicator)
SW1
R4
10K
J2
DC-
J3
DC+
DS1
Schottky
L1
J1
1
2
3
2.2µH
U1
VCC
1
JP1
2
3
4
C1
2.2µF
5
6
VIN
EN
SEL
VP
N/C
SW
LIN
OVP
FB
GND
PGND
SW
VOUT
R2
226K
12
11
10
R3
12K
9
8
7
AAT1231
R1
D6
D5
30.1Ω
LED
LED
D1
LED
D2
LED
D3
LED
C2
2.2µF
D4
LED
Figure 1: AAT1231 Evaluation Board Schematic with Six White LEDs and Microcontroller.
EV-130.2006.08.1.0
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EV-130
AAT1231 EVAL: Step-Up DC/DC Converter
for White LED Backlight Applications
Getting Started
The ballast resistor (R1) is set to 30.1Ω on the evaluation board. This sets the maximum LED current to 20mA.
ILED =
VFB
R1
Over-voltage protection is set to the maximum operation voltage (24V) to protect the IC from damage.
There are three (3) buttons on the evaluation board. The modes of operation are detailed in Table 1. Each
button controls a particular function. The SW1 (Up) button increments the number of EN/SET edges, and the
AAT1231 increases the FB pin voltage according to Table 2. By holding down the Up button for more than 1.5
seconds, the microcontroller enters auto-increment mode. The SW2 (Down) button decrements the number
of EN/SET edges and the AAT1231 decreases the FB pin voltage. By holding down the Down button for more
than 1.5 seconds, the microcontroller enters auto-decrement mode. The SW3 (Select) button toggles
High/Low on the SEL pin. A green LED (D8) indicates the status on the SEL pin. If the green LED turns ON,
the SEL pin is set to High. If the green LED turns off, the SEL pin is set to Low. Figure 2 details the LED nominal current levels for SEL=High and SEL=Low settings with R1=30.1Ω.
LED Current (mA)
25
20
SEL = HIGH
15
10
(Default)
SEL = LOW
5
0
1
4
7
10
13
16
S2Cwire Data Register
Ω.
Figure 2: Programming LED Current with RBALLAST = 30.1Ω
Upon initial power-up and prior to S2Cwire programming, the default FB pin voltage is set at 0.1V/0.3V depending on the SEL pin logic level. The red LED (D7) should illuminate, indicating that power has been connected
to the evaluation board.
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EV-130.2006.08.1.0
EV-130
AAT1231 EVAL: Step-Up DC/DC Converter
for White LED Backlight Applications
User Interface Functionality
Button(s) Pushed
SW1 (Up)
SW2 (Down)
SW3 (Select)
Description
[Push/Release once] Increment the number of EN/SET edges. Toggles through the
available brightness level settings for the backlighting section.
[Holding 1.5 sec.+] Auto-increment one voltage level per second.
[Push/Release once] Decrement the number of EN/SET edges. Toggles through the
available dimming level settings for the backlighting section.
[Holding 1.5 sec.+] Auto-decrement one voltage level per second.
[Push/Release once] Toggles the SEL logic pin High/Low.
Table 1: User Interface Functionality.
SEL = Low
SEL = High
Rising Clock
Edges/Data
Register
Reference
Voltage (V)
LED Current (mA);
Ω
RBALLAST = 30.1Ω
Reference
Voltage (V)
LED Current (mA);
Ω
RBALLAST = 30.1Ω
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
0.1 (default)
0.12
0.14
0.16
0.18
0.20
0.22
0.24
0.26
0.28
0.30
0.32
0.34
0.36
0.38
0.40
3.32
3.99
4.65
5.32
5.98
6.64
7.31
7.97
8.64
9.30
9.97
10.63
11.30
11.96
12.62
13.29
0.3 (default)
0.32
0.34
0.36
0.38
0.40
0.42
0.44
0.46
0.48
0.50
0.52
0.54
0.56
0.58
0.60
9.97
10.63
11.30
11.96
12.62
13.29
13.95
14.62
15.28
15.95
16.61
17.28
17.94
18.60
19.27
19.93
Ω
Table 2: AAT1231 S2Cwire Reference Feedback Voltage Control Settings with RBALLAST = 30.1Ω
(Assume Nominal Values).
EV-130.2006.08.1.0
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EV-130
AAT1231 EVAL: Step-Up DC/DC Converter
for White LED Backlight Applications
Printed Circuit Board
Figure 3: AAT1231 Evaluation
Board Top Layer (not to scale).
Figure 4: AAT1231 Evaluation
Board Bottom Layer (not to scale).
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EV-130.2006.08.1.0
EV-130
AAT1231 EVAL: Step-Up DC/DC Converter
for White LED Backlight Applications
AAT1231 EVAL Component Listing
Component
Part Number
Description
U1
AAT1231
U2
PIC12F675
Step Up DC-DC Converter for White LED
Backlight Applications; TSOPJW-12 Package
8-bit CMOS, FLASH-Based µC; 8-Pin
PDIP Package
Switch Tact, SPST, 5mm
30.1Ω, 1%, 1/4W; 0603
226kΩ, 1%, 1/4W; 0603
12.1kΩ, 1%, 1/4W; 0603
10kΩ, 5%, 1/4W; 0603
1kΩ, 5%, 1/4W; 0805
330Ω, 5%, 1/4W; 0805
0Ω, 5%, 0805
2.2µF, 10V, X5R, 0603
2.2µF, 25V, X7R, 0805
1µF, 10V, X5R, 0805
2.2µH, Core Shield
SW1 - SW3
R1
R2
R3
R4
R5, R6, R7
R8, R9
JP1
C1
C2
C3
L1
DS1
D1-D6
D7
D8
J1, J2, J3
PTS645TL50
Chip Resistor
Chip Resistor
Chip Resistor
Chip Resistor
Chip Resistor
Chip Resistor
Chip Resistor
GRM188R60J225KE01
GRM21BR71E225KA73
GRM216R61A105KA01
SD3814-2R2
BAT42W
LW M673
CMD15-21SRC/TR8
CMD15-21VGC/TR8
PRPN401PAEN
Schottky Diode; VR = 30V, IFM = 0.2A
SOD-123
White Hyper-Bright LED
Red LED; 1206
Green LED; 1206
Connecting Header, 2mm Zip
Manufacturer
AnalogicTech
Microchip
ITT Industries
Vishay
Vishay
Vishay
Vishay
Vishay
Vishay
Vishay
MuRata
MuRata
MuRata
Cooper Electronics;
Coiltronics
Diodes, Inc.
OSRAM
Chicago Miniature Lamp
Chicago Miniature Lamp
Sullins Electronics
Table 3: AAT1231 Evaluation Board Component Listing.
EV-130.2006.08.1.0
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EV-130
AAT1231 EVAL: Step-Up DC/DC Converter
for White LED Backlight Applications
© Advanced Analogic Technologies, Inc.
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.
Customers are advised 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.
AnalogicTech and the AnalogicTech logo are trademarks of Advanced Analogic Technologies Incorporated. All other brand and product names appearing in this document are registered trademarks or trademarks of their respective holders.
Advanced Analogic Technologies, Inc.
830 E. Arques Avenue, Sunnyvale, CA 94085
Phone (408) 737-4600
Fax (408) 737-4611
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EV-130.2006.08.1.0
Form#: FM-QA-001 Rev. 01