EVALUATION BOARD DATA SHEET EV171 Evaluation Board for the AAT2868 CABC Compatible Four-Channel Backlight Driver with Dual LDO Regulators Introduction The AAT2868 EVAL board demonstrates the functionality of the AAT2868 and its application as a backlight driver with dual LDO outputs. The AAT2868 is a low-noise, constant-frequency charge pump DC/DC converter that uses a dual-mode load switch (1x) and fractional (1.5x) conversion to maximize efficiency for white LED Content Adaptive Brightness Control (CABC) applications. The AAT2868 is capable of driving 4 white LEDs at a total of 124mA and two 150mA low dropout (LDO) linear regulators from a 2.7V to 5.5V input. All these functions can be programmed using the AS2Cwire™ interface. Skyworks' AS2Cwire™ serial digital input is used to enable, disable and set the maximum LED current to one of 32 levels for the LEDs. Each LED current ranges from 31mA to 0.4mA. An external PWM input is adopted to dim the LED current from 100% to 1% of the maximum LED current by varying the PWM duty cycle with frequencies up to 100kHz. The AS2Cwire interface is also used to enable and disable LDOs and set the LDOs' output voltages. Five output voltage levels and sixteen combinations of LDOA and LDOB can be set via the interface. This document describes the AAT2868 evaluation board and its accompanying user interface. A brief “Getting Started” section is also included to help the user to begin operating the evaluation board. The AAT2868 evaluation board is shown in Figure 1; Figures 2 and 6 depict the board schematic and layout. Figure 4 illustrates the functions of the three buttons on the EVAL board. For additional information, please consult the AAT2868 product datasheet. Board Picture (a) Top Side (b) Bottom Side Figure 1: AAT2868 Evaluation Board. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202289A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 23, 2012 1 EVALUATION BOARD DATA SHEET EV171 Evaluation Board for the AAT2868 CABC Compatible Four-Channel Backlight Driver with Dual LDO Regulators Evaluation Board Schematic U1 AAT2868 C1 1µF J1 1 18 7 6 DC+ V_LDO CIN 2.2µF DC- 8 5 AAT2868 White LED Driver R1 0 D1 FCAP CF 56nF EP D1 D2 D3 D4 LDOA LDOB R2 0 R3 0 R4 0 D3 D2 10 11 12 13 3 D4 LDOA 2 LDOB CLDOB 2.2µF PWM CLDOA 2.2µF EN/SET R10 R11 R12 1k 1k 1k SELECT R7 50k VOUT COUT 1µF EN/SET PWM 9 R8 50k C2 1µF 16 15 17 GND AGND 14 4 V _MCU C2+ C2OUTCP C1+ C1IN INLDO 1 2 3 4 U2 VDD GP5 GP4 GP3 PIC12F675 VSS GP0 GP1 GP2 C3 0.1µF 8 7 6 5 R9 1k LED2 Red R6 1k DETAIL LED1 SEND AS2Cwire Microcontroller Figure 2: AAT2868 Evaluation Board Schematic. 2 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202289A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 23, 2012 EVALUATION BOARD DATA SHEET EV171 Evaluation Board for the AAT2868 CABC Compatible Four-Channel Backlight Driver with Dual LDO Regulators Getting Started The board has two terminals labeled DC+ and DC- for the input power supply connection. Set J1 to the left position; jump the V_MCU and apply 2.7V to 5.5V power to the DC+ and DC- terminals to power the AAT2868 (U1) and microcontroller (U2); the red LED (LED2) should illuminate when the microcontroller is powered. EN/SET option provides access to the microcontroller program. Jump the EN/SET terminal when using microcontroller program to generate AS2Cwire data for the AAT2868. Figure 3 shows the connection of the AAT2868 board. Figure 3: AAT2868 Evaluation Board Demonstration Connection. The three buttons on the AAT2868 evaluation board are used to set address and data for the registers and send the selected address and data to the AAT2868 through the EN/SET signal line. Figure 4 shows the functions of the three buttons. Button Functions Three buttons are located on the evaluation board: SELECT, DETAIL, and SEND. The SELECT button is used to select a register address. Each press of the SELECT button selects a register address from 0 to 5 then wraps back to 0 (register address 1 is reserved and the processor program is designed to skip this address selection). The DETAIL button is used to select data for a particular address register. The SEND button sends the selected address and data to the EN/SET signal line. Details of the button functions are shown in Figure 4. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202289A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 23, 2012 3 EVALUATION BOARD DATA SHEET EV171 Evaluation Board for the AAT2868 CABC Compatible Four-Channel Backlight Driver with Dual LDO Regulators SELECT Button DETAIL Button Pressed times Register Addr. 0 1 2 Backlight MSB 2 3 Backlight LSBs 3 4 LDO Enable/Disable 4 5 LDO Output Voltage Selected Register Addr. 0 Addr. 2 Three Button Functions Addr.3 Addr. 4 Addr. 5 SEND Button Register Function 0 Backlight Enable Pressed times 0 Detail selected Backlighting Enable 1 Backlighting Disable 0 BL[4] = 0 1 BL[4] = 1 0 BL[3~0] = 0000 1 BL[3~0] = 0001 15 BL[3~0] = 1111 0 LDOA off, LDOB off 1 LDOA off, LDOB on 2 LDOA on, LDOB off 3 LDOA on, LDOB on 0 LDOA=3.0V LDOB=2.8V 1 LDOA=3.0V LDOB=1.8V 2 LDOA=3.0V LDOB=1.5V 3 LDOA=3.0V LDOB=1.2V 4 LDOA=2.8V LDOB=2.8V 5 LDOA=2.8V LDOB=1.8V 6 7 LDOA=2.8V LDOB=1.5V LDOA=2.8V LDOB=1.2V 8 LDOA=1.8V LDOB=2.8V 9 LDOA=1.8V LDOB=1.8V 10 LDOA=1.8V LDOB=1.5V 11 LDOA=1.8V LDOB=1.2V 12 LDOA=1.5V LDOB=2.8V 13 LDOA=1.5V LDOB=1.8V 14 LDOA=1.5V LDOB=1.5V 15 LDOA=1.5V LDOB=1.2V Send Selected Address and Data through EN/SET Signal Line Figure 4: Button Functions of the AAT2868 Evaluation Board. 4 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202289A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 23, 2012 EVALUATION BOARD DATA SHEET EV171 Evaluation Board for the AAT2868 CABC Compatible Four-Channel Backlight Driver with Dual LDO Regulators LED Current Control AS2Cwire Interface The LED current can be programmed from 0.4mA to 31mA with 32 steps via the AS2Cwire interface. Address 3 and 2 with 5 bits from BL[0] to BL[5] are used to set the LED current value as shown in Table 1. Addr2 Addr3 LED Current Codes BL4 BL3 BL2 BL1 BL0 LED Current (mA) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0.4 0.9 1.9 2.9 3.9 4.9 6.0 7.0 8.0 9.0 10.0 11.0 12.0 13.0 14.0 15.0 16.0 17.0 18.0 19.0 20.0 [Default] 21.0 22.0 23.0 24.0 25.0 26.0 27.0 28.0 29.0 30.0 31.0 Table 1: AAT2868 Maximum LED Current Set Registers. The LED current changes to the programmed value only after the “Backlight LSBs” register is written. For example, the LED current settings can be reset from the default setting of 20mA to 31mA via the following steps: 1. 2. 3. 4. 5. 6. Press Press Press Press Press Press the the the the the the SELECT button to select the Address 2 “Backlight MSB” register. DETAIL button to set BL[4] to 1. SEND button to send the selected address and data to AAT2868 via the EN/SET pin. SELECT button to select Address 3 “Backlight LSBs” register. DETAIL button to set BL[3~0] to 1111. SEND button to set each LED's current to 31mA. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202289A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 23, 2012 5 EVALUATION BOARD DATA SHEET EV171 Evaluation Board for the AAT2868 CABC Compatible Four-Channel Backlight Driver with Dual LDO Regulators PWM Interface An external PWM signal with a frequency of 1kHz to 100kHz and duty cycle varying from 100% to 1% can be fed into the AAT2868's PWM pin to dim the LED current from the programmed maximum value to 1% of maximum through the PWM terminal on the board for CABC applications. Figure 5 shows an example of linear change of the LED current level as the PWM duty cycle varies with the current level set to a maximum of 20mA. 22 20 18 ILED (V) 16 14 12 10 8 6 4 2 0 100 95 90 85 80 75 70 65 60 55 50 45 40 35 30 25 20 15 10 5 0 PWM Duty Cycle (%) Figure 5: LED Current Dimming vs. PWM Duty Cycle (Maximum Current = 20mA). LDO Control The AAT2868 includes two LDOs: LDOA and LDOB. The LDOs' enable, disable, and output voltage values are controlled by writing register through AS2Cwire interface. Figure 4 shows how to use the three buttons on the evaluation board to select and send LDO settings. Printed Circuit Board (a) Top Layer (b) Bottom Layer Figure 6: AAT2868 Evaluation Board Layout. 6 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202289A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 23, 2012 EVALUATION BOARD DATA SHEET EV171 Evaluation Board for the AAT2868 CABC Compatible Four-Channel Backlight Driver with Dual LDO Regulators AAT2868 EVAL Component List Component Part Number Description Manufacturer U1 U2 R1, R2, R3, R4 R7, R8 R6, R9, R10, R11, R12 C1, C2, COUT CIN, CLA, CLB C3 CF D1, D2, D3, D4 LED1 LED2 CYCLE,UP, DOWN AAT2868IDT-T1 PIC12F675 RC0603FR-070RL RC0603FR-0749K9L RC0603FR-071KL GRM188R71C105K GRM188R61A225K GRM188R71C104K GRM188R71C563K RS-0805UW 0805KGCT 0805KRCT 6*6*5 High Efficiency, 4 Channel Backlight Driver with Dual LDOs 8-Pin FLASH-Based 8-Bit CMOS Microcontroller Res 0Ω 1/10W 1% 0603 SMD Res 49.9KΩ 1/10W 1% 0603 SMD Res 1KΩ 1/10W 1% 0603 SMD Cap Ceramic 1μF 0603 X7R 16V 10% Cap Ceramic 2.2μF 0603 X5R 10V 10% Cap Ceramic 0.1µF 0603 X7R 16V 10% Cap Ceramic 0.056μF 0603 X7R 16V 10% 20mA White LED 0805 Green LED 0805 Red LED 0805 12V 50mA Pushbutton Skyworks Microchip Yageo Murata Realstar HB E-LT Table 2: AAT2868 Evaluation Board Component List. 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Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202289A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 23, 2012 7