Freescale Semiconductor Application Note Document Number: AN4292 Rev 0, 10/2012 DEMOMMA8491 Xtrinsic Accelerometer Evaluation Kit by: FengYi Li Applications Engineer This application note provides an overview of the Xtrinsic DEMOMMA8491 kit and its evaluation guidelines. The DEMOMMA8491 kit contains two boards: • Demo board: provides a tamper detection sensor demonstration using the Xtrinsic MMA8491Q 45° tilt sensor and 3-axis accelerometer, housed in a transparent plastic case. • Breakout board: provides easy access to every pin of the QFN sensor for evaluation. This document describes board functionality and features, how to use these boards, and what to look for when evaluating the devices. The last section provides reference schematics and the bills of materials. © 2012 Freescale Semiconductor, Inc. All rights reserved. Contents 1 2 3 4 DEMOMMA8491 Demo Board . . . . . . . . . . . . . . . . . . . . 1.1 Acceleration directions . . . . . . . . . . . . . . . . . . . . . . 1.2 Using the demo board . . . . . . . . . . . . . . . . . . . . . . . 1.3 Acceleration values are cumulative . . . . . . . . . . . . . DEMOMMA8491 Breakout Board . . . . . . . . . . . . . . . . . . 2.1 Pin map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2 Suggested application connections . . . . . . . . . . . . . 2.3 Soldering considerations . . . . . . . . . . . . . . . . . . . . . 2.4 Evaluating performance. . . . . . . . . . . . . . . . . . . . . . Schematics and Bill of Materials (BOM) . . . . . . . . . . . . . 3.1 Demo board schematic . . . . . . . . . . . . . . . . . . . . . . 3.2 Demo board BOM . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3 Breakout board schematic. . . . . . . . . . . . . . . . . . . . 3.4 Breakout board BOM. . . . . . . . . . . . . . . . . . . . . . . . Revision History. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 2 2 3 4 4 5 5 6 6 6 6 7 7 8 1 DEMOMMA8491 Demo Board The demo board of the DEMOMMA8491 kit is an out-of-the-box 3-axis MEMS tilt sensor. It showcases a simple tilt sensor implemented with the MMA8491Q device, with 10 additional passive components. Figure 1. DEMMMA8491 demo board 1.1 Acceleration directions The demo board uses the acceleration directions in Figure 2. The left image shows the acceleration direction on the MMA8491Q device. The right image shows the acceleration direction of the demo board. Figure 2. Sensor orientation 1.2 Using the demo board The demo is powered by a 3V coin battery and is controlled by one switch button (SW1). When the switch is pressed, the tilt sensor is powered on, and it takes one sample of the current acceleration. The tilt detection result is simultaneously displayed with 3 LEDs (each LED is paired with one of the X, Y, Z axes). A lit LED indicates that a tilt angle greater than or equal to 45° is detected on that axis. DEMOMMA8491 Xtrinsic Accelerometer Evaluation Kit, Rev 0 2 Freescale Semiconductor, Inc. To demonstrate the kit, hold the demo board to the desired position, then press and hold down the switch button. Make sure that your hand is steady. Observe the LEDs for a tilt report. Release the button to discard the sample. Figure 3 shows the LED status at 6 different orientations. • • LED X = 0 indicates that LED X is turned off. LED X = 1 indicates that LED X is turned on. Figure 3. LED states for different orientations 1.3 Acceleration values are cumulative The MMA8491Q device is a MEMS-based accelerometer. It picks up the acceleration signal (if it is present), and compares the acceleration to an internal threshold of 0.688g. When the demo board is held at a 45° angle, the acceleration reading along that axis (coming from the earth gravity) is about 0.688g. In this case, that axis's output (XOUT, YOUT or ZOUT) is triggered to logic high. When you provide external acceleration (other than the earth gravity) on the demo board, the tilt sensor reports the cumulative acceleration. As the result of these additional g-forces, you might observe positive tilt detection when the board is at a position less than a 45°angle. DEMOMMA8491 Xtrinsic Accelerometer Evaluation Kit, Rev 0 Freescale Semiconductor, Inc. 3 2 DEMOMMA8491 Breakout Board For evaluating the MMA8491Q industrial 12-pin QFN tilt sensor, the breakout board provides practical and efficient access, with minimum soldering work. J1-1 J3-1 J1-2 J3-2 J1-3 J3-3 J2-1 J2-2 J2-3 Figure 4. Breakout board The DEMOMMA8491 breakout board has fanned out all of the MMA8491Q pins, except the bypass pin (BYP). It has three top-layer components: the MMA8491Q device and two 0.1 uF ceramic capacitors (C1, C2). The board itself is a two-layer PCB, using a 0.1 inch pitch between the breakout pins. The device should have a 0.1 uF capacitor connected between the bypass pin (BYP) and ground. This requirement is satisfied with the capacitor C1. The device also needs a high frequency filter capacitor on VDD. This requirement is satisfied with the capacitor C2. These recommendations are listed in the MMA8491Q data sheet. 2.1 Pin map Table 1 maps the pins of the breakout board to the MMA8491Q device pins. Table 1. Breakout board to MMA8491Q sensor pins Breakout Board MMA8491Q Device Description Pin Status Pin Name Pin Name J1-1 VDD 2 Vdd Supply Voltage Input J1-2 EN 4 En Enable Accelerometer on logic 1 Input J1-3 GND 7 Gnd Ground plate Ground J2-1 SDA 4 SDA I2C bus data Ground J2-2 SCL 5 SCL I2C bus clock Input J2-3 GND 6 Gnd Ground J3-1 ZOUT 8 Zout Tri-state Z-Axis tilt detect output Input / Output Output DEMOMMA8491 Xtrinsic Accelerometer Evaluation Kit, Rev 0 4 Freescale Semiconductor, Inc. Table 1. Breakout board to MMA8491Q sensor pins (Continued) Breakout Board 2.2 MMA8491Q Device Description Pin Status Pin Name Pin Name J3-2 YOUT 9 Yout Tri-state Y-Axis tilt detect output Output J3-3 XOUT 10 Xout Tri-state X-Axis tilt detect output Output Suggested application connections To ensure that the accelerometer is fully functional, connect the breakout board as shown in Figure 5. VDD Xout EN Yout Pulsed EN signal Zout VDD VDD 4.7kΩ 4.7kΩ SDA SCL Figure 5. Example application with I2C bus engaged This connection follows the recommendations listed in MMA8491Q data sheet. • The power supply decoupling capacitor is placed as close as possible to the VDD pin. The 0.1 μF capacitor value has been chosen to minimize the average current consumption, while still maintaining an acceptable level of power supply high-frequency filtering. • When the I2C communication line is used, pullup resistors (one pullup resistor for each line) should be used to connect to SDA and SCL. If the SDA/SCL pins are not used, then they should be tied to ground. It is recommended that you use resistors no less than 1KΩ, to reduce the current load on the I2C bus. 2.3 Soldering considerations The breakout board is a top component two-layer PCB board, with device pins fanned out to 0.1 inch pitch copper pads. There is no special soldering handling requirement when using the breakout board—you can directly hand-solder wires to it. For more information about the standard MMA8491Q device mounting process, see the MMA8491Q data sheet. DEMOMMA8491 Xtrinsic Accelerometer Evaluation Kit, Rev 0 Freescale Semiconductor, Inc. 5 2.4 Evaluating performance When evaluating the MMA8491Q tilt sensor performance using the breakout board, consider offset factors: • Offset variation over temperature • Board mount offset • Breakout-board-to-system alignment For offset variation and board mount offset data, see the MMA81941Q data sheet. We suggest that you perform a breakout-board-to-system alignment check. Typically, the tilt sensor axes may not exactly align with the axes of the customer's system. This misalignment translates to the cross-axis offset, effectively changing the tilt detection angle. A system adjustment helps to get a more accurate evaluation result. You can use the readouts from the MMA8491Q device via I2C bus for a coarse alignment check, without having to use a reference accelerometer. 3 Schematics and Bill of Materials (BOM) 3.1 Demo board schematic Figure 6. Demo board schematic 3.2 Demo board BOM Table 2. Demo board BOM Item Quantity Reference Value Description 1 1 BT1 CR2016-F2N 2 2 C1, C2 GRM188R71H104KA93D 3 3 D1, D2, D3 HLMP-Q156-H0011 LED, RED SGL 50MA SMT 4 3 R1, R2, R3 RK73H1JTTD6800F Resistor, MF 680 OHM 1/10W 1% 0603 Battery, lithium coin, 3V 90MAH 20MM PCB SMT Capacitor, ceramic, 0.1UF 50V 10% X7R 0603 DEMOMMA8491 Xtrinsic Accelerometer Evaluation Kit, Rev 0 6 Freescale Semiconductor, Inc. Table 2. Demo board BOM (Continued) Item Quantity Reference Value 5 1 SW1 EVQQ2B03W 6 1 U1 MMA8491Q 3.3 Description Switch SPST, PB NO 0.5N 20MA 15V SMT IC, 3-axis low voltage tilt sensor 1.95–3.6V QFN12 Breakout board schematic Figure 7. Breakout board schematic 3.4 Breakout board BOM Table 3. Breakout board BOM Item Quantity Reference Value 1 1 U1 MMA8491Q 2 2 C1,C2 GRM188R71H104KA93D Description IC, 3-axis low voltage tilt sensor 1.95–3.6V QFN12 Capacitor, ceramic, 0.1UF 50V 10% X7R 0603 DEMOMMA8491 Xtrinsic Accelerometer Evaluation Kit, Rev 0 Freescale Semiconductor, Inc. 7 4 Revision History Revision 0 is the initial release of this document. DEMOMMA8491 Xtrinsic Accelerometer Evaluation Kit, Rev 0 8 Freescale Semiconductor, Inc. How to Reach Us: Information in this document is provided solely to enable system and software Home Page: freescale.com implementers to use Freescale products. There are no express or implied copyright Web Support: freescale.com/support information in this document. licenses granted hereunder to design or fabricate any integrated circuits based on the Freescale reserves the right to make changes without further notice to any products herein. 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