Introduction EVALUATION BOARD DATA SHEET The AAT1278 evaluation board demonstrates the functionality of the AAT1278 and its application as LED photo flash driver under Skyworks' AS 2 Cwire serial digital interface control. The AAT1278 is a boost converter with a programmable constant current LED driver with an input voltage range of 2.7V to.v. The single flash LED driver delivers up to 100mA output current in flash mode. An external resistor is employed to set the flash LED maximum current for flash and movie modes; the movie mode LED current can be easily programmed from 100% to 0% of the maximum current value in 16 steps with a single GPIO output via the AS 2 Cwire interface; the flash to movie mode ratio can also be easily programmed from 2:1 to OFF in 16 steps with a single GPIO output via the AS 2 Cwire interface and the fixed flash to movie mode ratio is 7.3:1.The wide input voltage range, small solution size, and high switch frequency is suitable for small battery-powered applications. This document describes the evaluation board and its accompanying user interface. A Getting Started section is included to help the user to begin operating the evaluation board. The AAT1278 evaluation board is shown in Figure 1; Figures 2 and 6 depict the board schematic and layout. For additional information, please consult the AAT1278 product datasheet and application note (AN-111) for understanding of the AS 2 Cwire serial digital interface. Board Pictures (a) Top Side. Figure 1: AAT1278 Evaluation Board Picture. (b) Bottom Side. 1
Board Schematic VIN GND Movie Mode Control Flash/Movie Mode Current Ratio FLEN JP1 MCU SW1 0 2 1 4 3 SW2 0 2 1 4 3 SW3 0 2 1 4 3 Getting Started R 10K R6 10K R7 10K JP3 EN/SET U2 1 VDD 2 GP 3 GP4 4 GP3 PIC12F67 VSS GP0 GP1 GP2 8 7 6 C3 1µF R9 330 R2 100K LED2 GRN C4 NA R8 330 LED1 RED C1 2.2µF Figure 2: AAT1278 Evaluation Board Schematic. R3 10k U1 A3 AGND RSET B1 A1 EN/SET FLGND C2 C1 FL A2 FLEN FLINHIBIT C3 SW B3 B2 IN SW B4 A4 OUT C4 PGND AAT1278 CSP-12 The board has two terminals labeled VIN and GND for the input power supply connection. Jump the JP1 to connect the V IN power to microcontroller VDD and AAT1278 IN. Jump JP2 to connect the SW4 to AAT1278 FLINHIBIT pin for inhibiting flash current. Jump the JP3 to set the microcontroller to generate AS 2 C code signal for driving LED. After all jumpers are in the correct positions, apply power between 2.7V and.v to the V IN and GND terminals to power the AAT1278 (U1) and microcontroller (U2); the red LED (LED1) should illuminate when the microcontroller is powered. The green LED (LED2) should flicker when microcontroller sends the AS 2 C digital signal to AAT1278.Table1 shows the jumps function, Figure 3 shows the connection of the AAT1278 board. R10 100k FLINH 0 2 1 4 3 R4 100k (opt) SW4 JP2 R1 133k D1 L1 1µH V OUT C2 2.2µF 2
Jumper Name JP1 JP2 JP3 Description Jump JP1 MCU ON position to power on the microcontroller and AAT1278, Jump JP1 MCU OFF position to disconnect the power. Connect JP2 to active the Flash Inhibit function by push SW4. Jump JP3 low position to generate AS 2 C code signal from microcontroller to AAT1278, Jump JP3 high position to cut off the AS 2 C signal between microcontroller and AAT1278. Table 1: Jumpers Function Description User Interface Functionality Figure 3: AAT1278 Evaluation Board Demonstration Connection. The user interface is provided by four push buttons: MMC (SW1), FMM (SW2), FLEN (SW3) and FLINH (SW4). A summary of operational modes for each button is outlined in Table 2. Definition of Each Control MMC Movie Mode Control (SW1): Sets movie mode current. Each switch closure will incrementally decrease the movie mode current stating at 100% to 0% (off) in 16 steps. Refer to the AAT1278 datasheet for detailed explanations of movie mode operation. FMM Flash/Movie Mode Current Ratio Control (SW2): Sets Flash/Movie Mode Current Ratio. Each switch closure will incrementally decrease the flash/movie mode current ratio stating at 2:1 to 0% (off) in 16 steps. Refer to the AAT1278 datasheet for detailed explanations of Flash to Maximum Movie Mode Current Ratio operation. FLEN Manual Flash Enable (SW3): Initiates a flash of maximum flash current. FLINH Inhibit Flash (SW4): Inhibit a flash current into default movie-mode current level 3
Button(s) SW1(MMC) SW2(FMM) SW3(FLEN) SW3(FLEN)+SW4(FLINH) Description LED Drive Current Set-Up [Push/Release once per step] Movie mode LED current dimming control. Each switch closure will issue an AS2C command to increment the data of the movie mode current register bits There are 16 steps in this register to step movie mode current from full scale to off (refer to the AAT1278 product datasheet for additional information). [Push/Release once per step] Flash/Movie Mode Current Ratio Control. Each switch closure will issue an AS2C command to increment the data of the Flash/Movie Mode Current Ratio register bits There are 16 steps in this register to step Flash/Movie Mode Current Ratio from 2:1 to off (refer to the AAT1278 product datasheet for additional information). [Push/Release once] Flash enable. Manually enables the AAT1278 boost converter to get the maximum flash current, initiates a single flash pulse. [Push SW4 and hold, then Push/Release SW3 once] Flash inhibit. Manually inhibit a flash current and enables the AAT1278 boost converter to get the maximum movie mode current, initiates a single flash pulse. Table 2: User Interface Functionality. LED Drive Current The AAT1278 can be set up to provide 1.A maximum flash mode current. The maximum flash mode current is set by R1 and can be set to 107kΩ for a maximum flash LED drive current of 1.A. In this AAT1278 manual s application R1 is set to 133kΩ for 1.2A maximum flash current. Flash current can be calculated using Equation1 by change the value of R1. Refer to the AAT1278 datasheet to program a desired flash current, the default maximum Movie Mode Current can be calculated using Equation2 in this AAT1278 manual. I FL = 162kΩ A 1200mA I MOVIE MODE = I FL (FL to MM Ratio) = = 164.4mA 7.3 AS²Cwire Interface and Control JP3 connects GPIO (U2) and AAT1278 (U1) AS 2 Cwire interface EN/SET, AS 2 Cwire interface data is programmed by the microcontroller U2 and its associated push button function switches SW1, SW2. The movie current can be programmed from 100% to 0% of the maximum movie mode current in 16 linear steps controlled by AS 2 Cwire data signal as shown in Table 3.The flash to movie mode ratio may be varied from 2:1 to OFF in 16 linear steps controlled by AS 2 Cwire data signal as shown in Table 4, the default ratio between the flash current level and maximum movie mode current level is 7.3:1. R 1 4
Data Percentage of Maximum MM Current 1* 100% 2 89% 3 79% 4 71% 63% 6 6% 7 0% 8 4% 9 40% 10 36% 11 32% 12 28% 13 2% 14 22% 1 20% 16 0% Table 3: Movie Mode (MM) Current Programming. Data Flash to Movie Mode Ratio 1 2:1 2 3.8:1 3.:1 4* 7.3:1 8.9:1 6 10.:1 7 12.2:1 8 13.8:1 9 14.9:1 10 16.:1 11 18:1 12 19.6:1 13 21.1:1 14 22.6:1 1 24:1 16 OFF Table 4: Flash/Movie Mode Current Ratio.
Test Waveform Movie Mode Waveform Figure 4 shows the waveform under movie mode controlled by AS 2 Cwire with data code.the I OUT rises to 100mA (63% of maximum movie mode current) as expected. Figure 4: Movie Mode Current Controlled by AS 2 Cwire Data (Ch1: V OUT ; Ch2: EN/SET; Ch3: I IN ; Ch4: I OUT ). 6
Maximum Flash Current Waveform Figure shows the AAT1278 Flash Current waveform with a FLEN pulse. I OUT maintains 1.2A when the flash enable pulse is asserted. Figure : Flash Current Operation with FLEN Pulse (Ch1: V OUT ; Ch2: FLEN; Ch3: I IN ; Ch4: I OUT ). 7
Maximum Movie Mode Current Waveform Figure 6 shows the AAT1278 Maximum Movie Mode Current waveform with a FLINH pulse, while FLEN is keeping high. I OUT maintains 164mA when the FLINH pulse is asserted. Figure 6: Complete Flash current operation waveform (Ch1: FLINH pulse; Ch2: FLEN; Ch4: I OUT ). 8
Printed Circuit Board EVALUATION BOARD DATA SHEET (a) Top Layer. AAT1278 EVAL Component Listing Figure 6: AAT1278 Evaluation Board. (b) Bottom Layer. Component Part Number Description Manufacturer U1 AAT1278 1.A Step-Up Current Regulator for Flash LED; Skyworks U2 PIC12F67 8-Pin FLASH-Based 8-Bit CMOS Microcontrollers Microchip SW1 SW4 PTS64TL0 Switch Tact, SPST, mm ITT Industries R1 Chip Resistor 133kΩ, 1%, 1/4W,0402 R2, R4, R10 Chip Resistor 100kΩ, 1%, 1/4W,0603 Vishay R3, R, R6, R7 Chip Resistor 10kΩ, %, 1/4W,0603 R8, R9 Chip Resistor 330Ω, %, 1/4W,0603 C1, C2 GRM188R71A22KE1 2.2μF, 10V, X7R, 0603 C3 GRM188R71C10K 1μF, 16V, X7R, 0603 MuRata C4(No Mounted) L1 SD3812-1R0-R Drum Core, 1μH, 2.69A, 48mΩ Cooper Bussmann LED1 080KRCT Red LED,080 LED2 080KGCT Green LED,080 HB JP1, JP2, JP3 PRPN401PAEN Conn. Header, 2mm zip Sullins Electronics D1 FCW401Z4 White Flash LED Seoul Semiconductor Table : AAT1278 Evaluation Board Bill of Materials. 9
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