EVALUATION BOARD DATA SHEET EV183 Evaluation Board for the AAT2822/2823/2824/2825 TFT-LCD DC-DC Converter with WLED Driver and VCOM Buffer Introduction The AAT282x family (AAT2822, AAT2823, AAT2824, AAT2825) of integrated panel power solutions provides the regulated voltages required by an active-matrix thin-film transistor (TFT) liquid-crystal display (LCD). The AAT282x family includes a boost DC-DC converter for LCD bias up to 14.5V, two charge pumps up to ±30V, a WLED backlight driver up to 28V, and a VCOM buffer in a 4 mm x 4mm TQFN package. The AAT282x have power sequence of VAVDD -> VGH -> VGL. The AAT282x-1 have power sequence of VAVDD -> VGL -> VGH. This document highlights the use of the AAT282x family evaluation board to demonstrate the functions and performance of the AAT282x power ICs. A brief “Getting Started” section is included to help the user to set up and operate the evaluation board. The board is shown in Figure 1. Figure 2 and Figure 15 depict the board schematic and layout. For additional information, refer to the AAT282x product datasheets. Board Pictures (a) Top (b) Bottom Figure 1: AAT282xIBK Evaluation Board. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202319A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 30, 2012 1 EVALUATION BOARD DATA SHEET EV183 Evaluation Board for the AAT2822/2823/2824/2825 TFT-LCD DC-DC Converter with WLED Driver and VCOM Buffer Board Schematic WLED- VIN 10V C1 4.7μF VIN-WLED R20 0Ω J3 C4 HF-PWM R1 0Ω VIN adj 10V C2 0.1μF PWM R21 0Ω OVP 10μF 16V 15 10kΩ 19 20 21 OVP WFB WCOMP VOPIN C22 0.1μF stage 2 C18 0.22μF 25V 6 13 R11 4 C19 0.22μF 50V J5 3 0.1μF 50V BAT54SDW A3 200kΩ LX C8 100pF 1 C20 0.22μF 50V 6 0.1μF 50V 5 4 C21 0.22μF 50V C14 3 BAT54SDW VAVDD 0.6V R6 J1 FBP Adj C26 10pF R7 6.04kΩ 25V EN DRVP R18 open A1 C10 3 4 C11 6 1 VAVDD AVDD C16 0.22μF 25V J8 stage2 2 C17 0.22μF 50V BAT54SDW A4 3 J9 4 0.1μF 50V C28 R19 VIN 5 0.1μF 50V C27 VDD VIN 0Ω C15 0.1μF 50V Adj R3 6.04kΩ C3 10μF 10V L1 2.2μH D1 VIN 0.1μF 25V 2 stage 3 stage4 C12 C13 1 2 C6 22μF 25V 0.1μF 25V 5 J7 0.6V R2 14 stage3 1 2 1 2 16 R14 R13 1 2 1 1 2 17 C23 0.1μF 25V 2 WEN 1 2 18 5 6 1 C29 0.22μF J10 stage4 50V 1 2 J2 J6 COMP open 0Ω R15 10kΩ VDD A2 J4 23 FB 7 DRVN VIN 22 WEN DRVN R16 LX 0V OP+ OPIN C25 open 12 6 FBN PGND1 R9 Adj 5 AAT2822 REF FBP VGL (negative) 4 11 3 FBN R10 6.04kΩ C7 OP- VDD 0.22μF 6.3V OUT R23 open C9 100Ω 8.2nF R17 U1 PGND2 10 1.2V WLX EN 2 9 1 C5 2.2μF 50V VIN 24 WDIM WLED+ AGND D2 DRVP R4 adj 8 10kΩ R12 AGND L2 2.2μH WLX 0.6V R22 open C24 10nF 17.4kΩ OVP R5 WFB R8 0.1μF 50V VGH (positive) 2 BAT54SDW C30 0.22μF 50V Figure 2: AAT2822IBK Evaluation Board Schematic. 2 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202319A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 30, 2012 EVALUATION BOARD DATA SHEET EV183 Evaluation Board for the AAT2822/2823/2824/2825 TFT-LCD DC-DC Converter with WLED Driver and VCOM Buffer WLED- VIN 10V C1 4.7μF VIN-WLED R20 0Ω J3 C4 HF-PWM R1 0Ω VIN adj 10V C2 0.1μF PWM 10μF 16V DRVN 7 200kΩ LX C8 100pF stage 2 C18 0.22μF 25V 6 4 C19 0.22μF 50V J5 3 C13 0.1μF 50V BAT54SDW A3 1 stage4 C12 20 21 22 19 WFB WCOMP D1 C20 0.22μF 50V 6 C21 0.22μF 50V C14 0.1μF 50V 5 4 3 BAT54SDW VAVDD 0.6V R6 VIN J1 FBP C26 R18 open A1 C10 3 4 C11 6 1 VAVDD AVDD C16 0.22μF 25V J8 stage2 2 C17 0.22μF 50V BAT54SDW A4 3 J9 4 0.1μF 50V C28 R19 VIN 5 0.1μF 50V C27 VDD VIN 0Ω C15 0.1μF 50V Adj 10pF R7 6.04kΩ 25V EN DRVP 0.1μF 25V 2 stage 3 L1 2.2μH C6 22 μF 25V 0.1μF 25V 5 Adj R3 6.04kΩ C3 10μF 10V stage3 1 2 1 2 0.6V R2 R11 1 2 1 1 2 13 C23 0.1μF 25V 2 WEN 1 2 COMP 15 14 5 6 1 C29 0.22μF J10 stage4 50V 1 2 J2 J6 OVP FB 16 VDD A2 J4 23 WEN DRVN VIN N/C 17 LX 0V N/C 18 12 6 PGND1 R9 Adj 5 AAT2823 FBN 11 VGL (negative) 4 REF FBP FBN R10 6.04kΩ C7 N/C N/C VDD 0.22μF 6.3V 3 C9 8nF U1 PGND2 10 1.2V WLX EN 2 9 1 C5 2.2μF 50V VIN 24 WDIM WLED+ AGND D2 C25 open R12 DRVP R4 adj 8 10kΩ R23 open 17.4kΩ AGND L2 2.2μH WLX 0.6V R22 open R21 0Ω OVP OVP R5 WFB R8 0.1μF 50V VGH (positive) 2 BAT54SDW C30 0.22μF 50V Figure 3: AAT2823IBK Evaluation Board Schematic. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202319A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 30, 2012 3 EVALUATION BOARD DATA SHEET EV183 Evaluation Board for the AAT2822/2823/2824/2825 TFT-LCD DC-DC Converter with WLED Driver and VCOM Buffer VIN 10V C1 4.7μF R1 0Ω 10V C2 0.1μF C24 10nF 100Ω R17 7 stage 2 C18 0.22μF 25V 6 19 20 N/C 22 21 VIN N/C 13 R11 4 C19 0.22μF 50V J5 3 0.1μF 50V BAT54SDW A3 200kΩ LX C8 100pF 1 C20 0.22μF 50V 6 C14 0.1μF 50V 5 4 C21 0.22μF 50V C3 10μF 10V L1 2.2μH D1 VAVDD 0.6V R6 VIN J1 FBP 3 BAT54SDW C26 R18 open A1 C10 3 4 C11 6 1 VAVDD AVDD C16 0.22μF 25V J8 stage2 2 C17 0.22μF 50V BAT54SDW A4 3 J9 4 0.1μF 50V C28 R19 VIN 5 0.1μF 50V C27 VDD VIN 0Ω C15 0.1μF 50V Adj 10pF R7 6.04kΩ 25V EN DRVP 0.1μF 25V 2 stage 3 stage4 C12 C13 1 2 Adj R3 6.04kΩ C6 22 μF 25V 0.1μF 25V 5 J7 0.6V R2 14 LX PGND1 C22 0.1μF stage3 1 2 1 2 10kΩ 1 2 1 1 2 15 VOPIN C23 0.1μF 25V 2 WEN 1 2 16 R14 R13 5 6 1 0.1μF 50V C29 0.22μF 50V VGH (positive) 2 BAT54SDW J10 stage4 1 2 J2 J6 COMP 18 17 VDD A2 J4 open 0Ω R15 10kΩ 12 DRVN DRVN VIN OPIN FB 11 0V OP+ WEN FBP R9 Adj 6 FBN VDD VGL (negative) 5 AAT2824 REF EN R10 6.04kΩ C7 OP- 9 4 OUT PGND2 10 3 FBN R16 U1 N/C 8 1.2V 0.22μF 6.3V N/C 24 N/C 2 DRVP 1 AGND 23 AGND C30 0.22μF 50V Figure 4: AAT2824IBK Evaluation Board Schematic. 4 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202319A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 30, 2012 EVALUATION BOARD DATA SHEET EV183 Evaluation Board for the AAT2822/2823/2824/2825 TFT-LCD DC-DC Converter with WLED Driver and VCOM Buffer VIN 10V C1 4.7μF R1 0Ω 10V C2 0.1μF 20 21 19 N/C N/C N/C 0.6V R2 14 13 R11 LX 200kΩ LX C8 100pF L1 2.2μH D1 C19 0.22μF 50V J5 3 C13 0.1μF 50V BAT54SDW A3 1 C20 0.22μF 50V 6 C21 0.22μF 50V C14 0.1μF 50V 5 4 3 BAT54SDW 0.6V R6 VIN J1 FBP C26 R18 open A1 C10 3 4 C11 6 1 VAVDD AVDD C16 0.22μF 25V J8 stage2 2 C17 0.22μF 50V BAT54SDW A4 3 J9 4 0.1μF 50V C28 R19 VIN 5 0.1μF 50V C27 VDD VIN 0Ω C15 0.1μF 50V Adj 10pF R7 6.04kΩ 25V EN DRVP 0.1μF 25V 2 stage 3 stage4 C12 0.1μF 25V 5 4 VAVDD C6 22 μF 25V stage3 1 2 stage 2 C18 0.22μF 25V 6 Adj R3 6.04kΩ C3 10μF 10V 5 6 1 C29 0.22μF J10 stage4 50V 1 2 1 2 15 1 2 1 1 2 16 C23 0.1μF 25V 2 WEN 1 2 17 12 7 J2 J6 COMP 18 VDD A2 J4 22 23 DRVN DRVN VIN VIN FB PGND1 R9 Adj N/C WEN FBP 6 0V AAT2825 FBN 11 5 N/C 10 VGL (negative) 4 REF EN FBN R10 6.04kΩ C7 N/C VDD 0.22μF 6.3V 3 N/C PGND2 8 1.2V U1 N/C DRVP 2 9 1 AGND N/C 24 AGND 0.1μF 50V VGH (positive) 2 BAT54SDW C30 0.22μF 50V Figure 5: AAT2825IBK Evaluation Board Schematic. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202319A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 30, 2012 5 EVALUATION BOARD DATA SHEET EV183 Evaluation Board for the AAT2822/2823/2824/2825 TFT-LCD DC-DC Converter with WLED Driver and VCOM Buffer Getting Started Setup 1. Connect an input power source (to supply between 2.5V and 5.5V) between VIN and ground. 2. Connect the jumpers to the positions shown in Figure 6. 3. Place the J2 jumper to the ON position before connecting the external WLED. To reduce inrush current, do not enable the main boost and the white LED driver concurrently. (a) Jumper Position when WLED Disabled b) Jumper Position when WLED Enabled Figure 6: AAT282x Evaluation Board Measurement Configuration. Table 1 shows the jumper functions. Jumper Description J1 J2 Enable the VAVDD, VGH, and VGL channels by setting the jumper EN from OFF to ON position. Enable the WLED by setting the jumper WEN from OFF to ON position. LED dimming control input to WDIM. Set to “100” position for maximum brightness and “0” position for shut down. Apply an external PWM signal up to 1 kHz to pin 2 of J3 by removing the jumper and adjust the duty cycle of the PWM signal from 100% to 5%, the LED brightness will change proportionally. Stage select for VGL channel with one of the three jumpers: J4 for two stages selection; J5 for three and J6 for four. Detail stage selection is discussed in section: “Boost and Dual Charge Pump Output Setting.” Stage select for VGH channel with one of the three jumpers: J4 for two stages selection; J5 for three and J6 for four. Detail stage selection is discussed in section: “Boost and Dual Charge Pump Output Setting.” Connect J7 OPIN for using VAVDD as VCOM buffer input voltage (VOPIN). The maximum input bias voltage for the VCOM buffer cannot exceed 13V. To prevent damage to the device when VAVDD is greater than 13V, OPIN should be connected to an external supply to the top pin of J7 by removing the jumper. J3 J4, J5, J6 J8, J9, J10 J7 Table 1: AAT282x Evaluation Board Jumper Functionality. 6 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202319A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 30, 2012 EVALUATION BOARD DATA SHEET EV183 Evaluation Board for the AAT2822/2823/2824/2825 TFT-LCD DC-DC Converter with WLED Driver and VCOM Buffer Functional Testing and Evaluation Measurement for Boost and Dual Charge Pumps The boost of LCD bias and dual charge pumps can be measured by test points of VAVDD, VGH and VGL. The boost output voltage can be set up to 14.5V and the outputs, VGH and VGL, of the two charge pumps can be set up to +30V and -30V by external resistor dividers. For details refer to the section: “Boost and Dual Charge Pumps Output Setting”. Figure 7 shows the configuration and the waveforms for the power up sequencing of the AAT282x-1 boost and the dual charge pumps. A 1Hz pulse signal is fed in to the Enable pin, EN. VIN is 5V, VAVDD is 10V, VGH is 18V, VGL is 20V. The waveform shows the power sequence is VAVDD -> VGL -> VGH. (a) Measurement Configuration (b) Waveform of AAT2822-1 Power-up Sequence Figure 7: AAT2822 Evaluation Board Boost and Dual Charge Pump Measurement. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202319A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 30, 2012 7 EVALUATION BOARD DATA SHEET EV183 Evaluation Board for the AAT2822/2823/2824/2825 TFT-LCD DC-DC Converter with WLED Driver and VCOM Buffer Measurement for WLED Backlight Driver The WLED backlight driver is a step-up DC-DC converter with sense resistor to provide feedback voltage. Its input voltage, VDD, on the board is either VAVDD with R19 set to 0Ω or external VIN with R18 set to 0Ω. The WLED brightness can be adjusted by either the PWM dimming or the ballast resistor (R8). The PWM signal can be fed in through WDIM pin at pin2 of jumper J3. The ballast resistor is used to set the maximum WLED current. For details refer to the section: “WLED Backlight”. Figure 8 shows the configuration and the measurement waveforms with R8 = 3Ω at 5V VIN. The current for each string is 20mA. In this configuration, 3 series 5 parallels WLEDs (3S5P), the total current is 100mA. (a) Measurement Configuration (b) Waveform for WLED 3S5P Configuration Figure 8: AAT2822 Evaluation Board Backlight Driver Measurement Operation. 8 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202319A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 30, 2012 EVALUATION BOARD DATA SHEET EV183 Evaluation Board for the AAT2822/2823/2824/2825 TFT-LCD DC-DC Converter with WLED Driver and VCOM Buffer Measurement for LCD VCOM Buffer The VCOM buffer is designed to drive the voltage on the backplane of an LCD display. The VCOM output voltage is typically set to half of the main boost output (VAVDD). Figure 9 shows the configuration for the measurement. The maximum input bias voltage for the VCOM buffer (VOPIN) cannot exceed 13V. To prevent damage to the device, connect VOPIN to an external supply when VAVDD is greater than 13V and leave the jumper J7 open to disconnect VAVDD from VOPIN. Figure 9: AAT282x Evaluation Board: Measurement Configuration for VCOM Buffer Output. Boost and Dual Charge Pump Output Setting The output voltage VAVDD of the LCD bias boost is set by external resistor divider R2 and R3. The dual charge pumps output voltages are determined by both resistor divider and charge pump stages. Table 2 shows the resistor divider selection equation and table 3 shows the charge pump stage selection equation. Output Channel Output Range VAVDD VIN - VDIODE to 14.5V VGL VDD to 30V VGH -VDD to -30V Equation For Adjustable Resistor R2 = R3 · VAVDD VAVDD VFB -1 = R3 · 0.6V - 1 VGL VGL R9 = V · R10 = 1.2V · R10 REF R6 = R7 · VGH VGH - 1 = R7 · -1 VFBP 0.6V Eq.1 Eq.2 Eq.3 Table 2: Resistor Divider Equations for Boost and Dual Charge Pumps. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202319A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 30, 2012 9 EVALUATION BOARD DATA SHEET EV183 Evaluation Board for the AAT2822/2823/2824/2825 TFT-LCD DC-DC Converter with WLED Driver and VCOM Buffer Charge Pump Equation For Stage Selection VGL nN = VGL 2VF - VAVDD(MIN) Eq.4 VGH nP = VGH - VAVDD(MIN) VAVDD(MIN) - 2VF Eq.5 Table 3: Charge Pump Stage Selection Equations. For example, if VAVDD = 5V, VGH = 18V and the forward voltage of the Schottky diode VF is 0.31V. nP = 18 - 5 = 2.97 5 - 2 · 0.31 So, to set VGH to 18V, three stages need to be used (J5 must be connected and J4, J6 left open). WLED Backlight WLED brightness can be adjusted either by setting the ballast resistor for max WLED current or by varying the duty cycle of the PWM signal. Ballast Resistor Selection The white LED driver can be enabled by setting J2 from OFF to ON position. The backlight current is set by an external ballast resistor (R8) up to a maximum of 260mA at 12V or 50mA at 28V. The AAT282x can drive from 3 WLEDs up to a maximum of 7 WLEDs in series. The number of WLEDs depends on the LCD panel size. Table 4 gives some examples of different LCD panel size and corresponding WLED configurations. The brightness of the white LED can be controlled by a PWM signal. By connecting a 1 kHz PWM signal to the WDIM pin and adjusting the duty cycle of the PWM signal from 100% to 5%, the brightness of the LED will change proportionally. The higher frequencies are achieved by filtered PWM and the value of R21, R22, R23, C25 should be calculated. See AAT2282 datasheet for more details. The equation for calculating OVP adjustable resistor (R4) is: R4 = R5 · VLED(MAX) VLED(MAX) VOVP -1 = R5 · 0.6V -1 where VLED(MAX) equals the forward voltage of the WLED series plus 0.3V VWFB. The equation for the number of series-connected LEDs is given by: N= VOVP(MIN) - VWFB(MAX) = VFLED(MAX) VOVP(MIN) - 0.3V 3.5V So, for example, when VOVP(MIN) = 28V, VWFB(MAX) = 0.3V, and VFLED(MAX) = 3.5V N= 28V - 0.6V 3.5V = 7.8 LEDs The maximum number of WLEDs in series for the given VOVP output range is, therefore, seven. 10 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202319A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 30, 2012 EVALUATION BOARD DATA SHEET EV183 Evaluation Board for the AAT2822/2823/2824/2825 TFT-LCD DC-DC Converter with WLED Driver and VCOM Buffer The equation for calculating ballast resistor (R8) is: R8 = 0.3V ILED(MAX) VWFB(MAX) = ILED(MAX) For example, for a 10-inch panel with 3 series and 13 parallel (3S13P) string configuration and the maximum current in each string being 20mA: R8 = WLED Matrix (Series and Parallel) 3S5P 0.3V = 1.15Ω 13 · 20mA Maximum ILED Current (mA) Ballast Resistor R8 (Ω) 5 10 15 20 25 30 12.0 6.0 4.0 3.0 2.4 2.0 WLED Matrix (Series and Parallel) 3S13P Maximum ILED Current (mA) Ballast Resistor R8 (Ω) 5 10 15 20 25 30 4.62 2.31 1.54 1.15 0.92 0.77 Table 4: Ballast Resistor Selection. Maximum WLED Output Current Maximum WLED output current is determined by both WLED driver input voltage VIN_WLED and WLED string voltage VLED. Figure 10 shows the relationship of the three factors. 600 ILED_MAX (mA) 500 V IN_WLED = 3.6V V IN_WLED = 4.2V 400 V IN_WLED = 5V V IN_WLED = 8V 300 V IN_WLED = 10V V IN_WLED = 12V V IN_WLED = 15V 200 V IN_WLED = 18V V IN_WLED = 20V 100 0 6 10 14 18 22 26 VLED (V) Figure 10: WLED Driver Maximum Output Current for different VLED Voltage. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202319A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 30, 2012 11 EVALUATION BOARD DATA SHEET EV183 Evaluation Board for the AAT2822/2823/2824/2825 TFT-LCD DC-DC Converter with WLED Driver and VCOM Buffer PWM Dimming The brightness of the white LED can be controlled using a PWM signal. By connecting a 1 kHz PWM signal to pin 2 of jumper J3 and adjusting the duty cycle of the PWM signal from 5% to 100%, the brightness of the LED will change proportionally. Figure 11 shows the variation of ILED with the PWM duty cycle. 20 18 16 ILED (mA) 14 12 10 8 6 4 2 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 PWM Duty Cycle (%) Figure 11: 1kHz PWM control (VIN = 5V, ILED(MAX) is set to 20mA). For applications requiring a PWM frequency higher than 1kHz, an external filter PWM is connected to the WFB pin to control the dimming of the white LED. Connect the PWM signal from "HF-PWM" test point and connect WDIM Pin to VIN. Figure 12 shows a low path filter used in the high frequency PWM control application. In this method, the LED dimming has relationship with both PWM high voltage level and duty cycle. WLEDadj VR8 I3 R8 R21 4.99k Connect WDIM to VIN I2 R22 VWFB 28k REF WCOMP 20 19 22 21 VIN OVP WFB OP+ AAT2822 FBN OPIN 18 17 16 15 14 13 LX COMP HF-PWM 12 11 8 7 10 DRVN PGND1 FB FBP WEN VDD 6 OP- EN 5 OUT R23 4.99k C25 0.1uF U1 PGND2 DRVP 4 WLX 9 3 AGND 24 2 WDIM 1 23 I1 VC25 Figure 12: Low-Pass Filter PWM Dimming Control. Figure 9: Low-Pass Filter PWM Dimming Control. 12 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202319A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 30, 2012 EVALUATION BOARD DATA SHEET EV183 Evaluation Board for the AAT2822/2823/2824/2825 TFT-LCD DC-DC Converter with WLED Driver and VCOM Buffer When the PWM duty cycle is adjusted, the average voltage on C25(VC25) will change. Because the VWFB is fixed at 0.3V, so I2 and I3 will change. The changed I3 will adjust the voltage drop, VDROP, across R21. The voltage across resistor R8, VR8, changes, leading to the change of the white LED current. Figure 13 shows PWM control by changing the PWM duty cycle with 2.4V high level and 0V low level. Figure 14 shows PWM control by varying the PWM high level with 50% fixed duty cycle. The following example illustrates the calculations for ILED in a 3S5P matrix where the PWM high level voltage is 1.2V, the frequency is 10kHz the duty cycle is 50%, and R8 = 3Ω. I3 = I1 + I2 = 0 + 1.2 - 0.3 2 28kΩ = 0.01mA VR8 = VWFB − I3 · R21 = 0.3 − 0.01mA · 4.99kΩ = 0.2501V ILED = VR8 R8 = 0.2501 = 83mA (Total current in 5 parallel strings) 3 Note: If the voltage in C25 is lower than VWFB, the current direction will reverse and I3 will equal I1 - I2. This will cause VR8 to be pulled up and decrease ILED. 20 18 16 I LED ᧤mA) 14 12 10 8 6 4 2 0 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 HF_PWM Duty Cycle (%) Figure 13: 10kHz High Frequency PWM Control by PWM Duty Cycle (VIN = 5V, ILED(MAX) = 20mA). Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202319A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 30, 2012 13 EVALUATION BOARD DATA SHEET EV183 Evaluation Board for the AAT2822/2823/2824/2825 TFT-LCD DC-DC Converter with WLED Driver and VCOM Buffer 20 18 16 14 I LED (mA) 12 10 8 6 4 2 0 0.6 1.2 1.8 2.4 3 3.6 4.2 4.8 High level of PWM Signal (V) Figure 14: 10kHz High Frequency PWM Control by PWM High Level Voltage (VIN = 5V, ILED(MAX) = 20mA). Printed Circuit Board (a) Top Layer (b) Bottom Layer Figure 15: AAT282xIBK Evaluation Board. 14 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202319A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 30, 2012 EVALUATION BOARD DATA SHEET EV183 Evaluation Board for the AAT2822/2823/2824/2825 TFT-LCD DC-DC Converter with WLED Driver and VCOM Buffer Layout Guidelines Use the following guidelines to ensure proper operation of the AAT282x: 1. Minimize the distance from the input capacitor negative terminal to the GND pins. 2. Maintain a ground plane and connect to the IC GND pin(s) as well as the GND connections of CIN and COUT. 3. Connect PGND and AGND as close as possible to the package and maximize the heat sinking space for overall performance. 4. To maximize package thermal dissipation and power handling capacity of the TQFN44-24 package, solder the exposed paddle of the IC onto the thermal landing of the PCB, where the thermal landing is connected to the ground plane. AAT282x EVAL Board Component Listing Component Part Number Description U1 AAT2822/3/4/5IBK C1 C2 C3, C4 C5 C6 C7 C8 C9 C10, C12, C22, C23 C11, C13, C14, C15, C27, C28 C16, C18 C17, C19, C20, C21, C29, C30 C24 C25 C26 A1, A2, A3, A4 D1, D2 L1, L2 GRM188R61A475K GRM188R71C104K GRM21BR61C106K GRM31CR71H225K GRM31CR61E226M GRM188R71A224K GRM1885C1H101J GRM2195C1H822J GRM188R61E104K TFT-LCD DC-DC Converter with WLED Driver and VCOM Buffer CAP CERAMIC 4.7μF 0603 X5R 10V 10% CAP CERAMIC 0.1μF 0603 X7R 16V 10% CAP CERAMIC 10μF 0805 X5R 16V 10% CAP CERAMIC 2.2μF 1206 X7R 50V 10% CAP CERAMIC 22μF 1206 X5R 25V 20% CAP CERAMIC 0.22μF 0603 X7R 10V10% CAP CERAMIC 100pF 0603 COG 50V 5% CAP CERAMIC 8.2nF 0805 X7R 50V 10% CAP CERAMIC 0.1μF 0603 X5R 25V 10% GRM188R71H104K CAP CERAMIC 0.1μF 0603 X7R 50V 10% GRM188R61E224K CAP CERAMIC 0.22μF 0603 X5R 25V10% GRM21BR71H224K CAP CERAMIC 0.22μF 0805 X7R 50V10% GRM188R71H103K NC GRM1885C1H100J BAT54SDW-7-F SS16L CDRH5D16-2R2 CAP CERAMIC 10nF 0603 X7R 50V 10% R2, R4, R6, R8, R9 R3, R7, R10 R5, R13, R14 R11 R12 R15, R19, R20, R21 R17 R16, R18, R22, R23, R25 RC0603FR-076K04L RC0603FR-0710KL RC0603FR-07200KL RC0603FR-0717K4L RC0603FR-070RL RC0603FR-07100RL CAP CERAMIC 10pF 0603 COG 50V 5% Schottky Diode Array 30V SC70-6 Schottky Diode 1A 60V Micro SMP POWER INDUCTOR 2.2μH 3.0A SMD Adjustable Value (See Equations 1 – 5 and Table 4); 0603 SMD Res 6.04kΩ 1/10W 1% 0603 SMD Res 10kΩ 1/10W 1% 0603 SMD Res 200kΩ 1/10W 1% 0603 SMD Res 17.4kΩ 1/10W 1% 0603 SMD Res 0Ω 1/10W 1% 0603 SMD Res 100Ω 1/10W 1% 0603 SMD Manufacturer Skyworks Murata Diode Inc Taiwan Semiconductor Sumida Yageo Not Populated Table 5: AAT2822 Evaluation Board Bill of Materials. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202319A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 30, 2012 15 EVALUATION BOARD DATA SHEET EV183 Evaluation Board for the AAT2822/2823/2824/2825 TFT-LCD DC-DC Converter with WLED Driver and VCOM Buffer Copyright © 2012 Skyworks Solutions, Inc. All Rights Reserved. Information in this document is provided in connection with Skyworks Solutions, Inc. (“Skyworks”) products or services. These materials, including the information contained herein, are provided by Skyworks as a service to its customers and may be used for informational purposes only by the customer. Skyworks assumes no responsibility for errors or omissions in these materials or the information contained herein. Skyworks may change its documentation, products, services, specifications or product descriptions at any time, without notice. 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Additional information, including relevant terms and conditions, posted at www.skyworksinc.com, are incorporated by reference. 16 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202319A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 30, 2012