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 1 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. 2 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 3 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). 4 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 5 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 6 EV-130.2006.08.1.0 Form#: FM-QA-001 Rev. 01