Freescale Semiconductor Technical Data Document Number: MMA6281QT Rev 1, 06/2007 ±2.5g - 10g Two Axis Low-g Micromachined Accelerometer The MMA6281QT low cost capacitive micromachined accelerometer features signal conditioning, a 1-pole low pass filter, temperature compensation and gSelect which allows for the selection among 4 sensitivities. Zero-g offset full scale span and filter cut-off are factory set and require no external devices. Includes a Sleep Mode that makes it idea l for handheld battery powered electronics. Features • • • • • • • • • • • MMA6281QT MMA6281QT: XZ AXIS ACCELEROMETER ±2.5g/3.3g/6.7g/10g Selectable Sensitivity (2.5g/3.3g/6.7g/10g) Low Current Consumption: 500 µA Sleep Mode: 3 µA Low Voltage Operation: 2.2 V – 3.6 V 6mm x 6mm x 1.45mm QFN Fast Turn On Time High Sensitivity (2.5 g) Integral Signal Conditioning with Low Pass Filter Robust Design, High Shocks Survivability Environmentally Preferred Package Low Cost Bottom View Typical Applications 16-LEAD QFN CASE 1622-02 MMA6281QT – 40 to +105°C 1622-02 QFN-16, Tray MMA6281QR2 – 40 to +105°C 1622-02 QFN-16,Tape & Reel 16 15 14 13 Sleep Mode g-Select1 1 12 g-Select2 2 11 N/C VDD 3 10 N/C VSS 4 9 N/C 5 6 7 8 N/C Package N/C Case No. N/C Temp. Range N/C Device N/C ORDERING INFORMATION ZOUT Top View N/C • • • • • • Portable Applications: Tilt Monitoring Anti-Theft Vibration Monitoring and Recording: Appliance Balance, Seismic, Smart Motors) Pedometer: Motion Sensing PDA: Text Scroll Navigation and Dead Reckoning: E-Compass Tilt Compensation Gaming: Tilt and Motion Sensing, Event Recorder Robotics: Motion Sensing Impact Monitoring (Shipping, Handling, Black Box Event Recorder) XOUT • • Figure 1. Pin Connections © Freescale Semiconductor, Inc., 2005-2007. All rights reserved. VDD g-Select1 g-Select2 G-Cell Sensor Sleep Mode Oscillator Clock Generator C to V Converter Gain + Filter Control Logic EEPROM Trim Circuits X-Temp Comp XOUT Z-Temp Comp ZOUT VSS Figure 2. Simplified Accelerometer Functional Block Diagram Table 1. Maximum Ratings (Maximum ratings are the limits to which the device can be exposed without causing permanent damage.) Rating Symbol Value Unit Maximum Acceleration (all axis) gmax ±2000 g Supply Voltage VDD –0.3 to +3.6 V Ddrop 1.8 m Tstg –40 to +125 °C Drop Test (1) Storage Temperature Range 1. Dropped onto concrete surface from any axis. ELECTRO STATIC DISCHARGE (ESD) WARNING: This device is sensitive to electrostatic discharge. Although the Freescale accelerometer contains internal 2000 V ESD protection circuitry, extra precaution must be taken by the user to protect the chip from ESD. A charge of over 2000 volts can accumulate on the human body or associated test equipment. A charge of this magnitude can alter the performance or cause failure of the chip. When handling the accelerometer, proper ESD precautions should be followed to avoid exposing the device to discharges which may be detrimental to its performance. MMA6281QT 2 Sensors Freescale Semiconductor Table 2. Operating Characteristics Unless otherwise noted: –20°C < TA < 85°C, 2.2 V < VDD < 3.6 V, Acceleration = 0g, Loaded output(1) Characteristic Symbol Min Typ Max Unit VDD IDD IDD TA 2.2 — — –40 3.3 500 3 — 3.6 800 10 +105 V µA µA °C gFS gFS gFS gFS — — — — ±2.5 ±3.3 ±6.7 ±10.0 — — — — g g g g VOFF 1.485 1.65 1.815 V VOFF, TA VOFF, TA ±2.6(6) ±1.0(6) ±0.6 ±0.8 ±3.8(7) ±0.8(7) mg/°C mg/°C S2.5g S3.3g S6.7g S10g 444 333 167 111 480 360 180 120 516 387 193 129 mV/g mV/g mV/g mV/g S,TA S,TA ±0.02(6) ±0.01(6) ±0.02 ±0.00 ±0.02(7) ±0.01(7) %/°C %/°C f-3dB f-3dB — — 350 150 — — Hz Hz nRMS nPSD — — 3.0 350 — — mVrms µg/ Hz tRESPONSE tENABLE — — 1.0 0.5 2.0 2.0 ms ms fGCELL fGCELL fCLK — — — 6.0 3.4 11 — — — kHz kHz kHz VFSO VSS+0.25 — VDD–0.25 V Nonlinearity, XOUT, ZOUT NLOUT –1.0 — +1.0 %FSO Cross-Axis Sensitivity(10) VXZ — — 5.0 % Operating Range(2) Supply Voltage(3) Supply Current Supply Current at Sleep Mode(4) Operating Temperature Range Acceleration Range, X-Axis, Z-Axis g-Select1 & 2: 00 g-Select1 & 2: 10 g-Select1 & 2: 01 g-Select1 & 2: 11 Output Signal Zero-g (TA = 25°C, VDD = 3.3 V)(5) Zero-g(4) X-axis Z-axis Sensitivity (TA = 25°C, VDD = 3.3 V) 2.5g 3.3g 6.7g 10g Sensitivity(4) X-axis Z-axis Bandwidth Response X Z Noise RMS (0.1 Hz – 1 kHz)(4) Power Spectral Density RMS (0.1 Hz – 1 kHz)(4) Control Timing Power-Up Response Time(8) Enable Response Time(9) Sensing Element Resonant Frequency X Z Internal Sampling Frequency Output Stage Performance Full-Scale Output Range (IOUT = 30 µA) 1. For a loaded output, the measurements are observed after an RC filter consisting of a 1.0 kΩ resistor and a 0.1 µF capacitor on VDD-GND. 2. These limits define the range of operation for which the part will meet specification. 3. Within the supply range of 2.2 and 3.6 V, the device operates as a fully calibrated linear accelerometer. Beyond these supply limits the device may operate as a linear device but is not guaranteed to be in calibration. 4. This value is measured with g-Select in 2.5g mode. 5. The device can measure both + and – acceleration. With no input acceleration the output is at midsupply. For positive acceleration the output will increase above VDD/2. For negative acceleration, the output will decrease below VDD/2. 6. These values represent the 10th percentile, not the minimum. 7. These values represent the 90th percentile, not the maximum. 8. The response time between 10% of full scale VDD input voltage and 90% of the final operating output voltage. 9. The response time between 10% of full scale Sleep Mode input voltage and 90% of the final operating output voltage. 10. A measure of the device’s ability to reject an acceleration applied 90° from the true axis of sensitivity. MMA6281QT Sensors Freescale Semiconductor 3 PRINCIPLE OF OPERATION The Freescale accelerometer is a surface-micromachined integrated-circuit accelerometer. The device consists of two surface micromachined capacitive sensing cells (g-cell) and a signal conditioning ASIC contained in a single integrated circuit package. The sensing elements are sealed hermetically at the wafer level using a bulk micromachined cap wafer. The g-cell is a mechanical structure formed from semiconductor materials (postillion) using semiconductor processes (masking and etching). It can be modeled as a set of beams attached to a movable central mass that move between fixed beams. The movable beams can be deflected from their rest position by subjecting the system to an acceleration (Figure 3). As the beams attached to the central mass move, the distance from them to the fixed beams on one side will increase by the same amount that the distance to the fixed beams on the other side decreases. The change in distance is a measure of acceleration. The g-cell beams form two back-to-back capacitors (Figure 3). As the center beam moves with acceleration, the distance between the beams changes and each capacitor's value will change, (C = Aε/D). Where A is the area of the beam, ε is the dielectric constant, and D is the distance between the beams. The ASIC uses switched capacitor techniques to measure the g-cell capacitors and extract the acceleration data from the difference between the two capacitors. The ASIC also signal conditions and filters (switched capacitor) the signal, providing a high level output voltage that is ratiometric and proportional to acceleration. Acceleration SPECIAL FEATURES g-Select The g-Select feature allows for the selection among 4 sensitivities present in the device. Depending on the logic input placed on pins 1 and 2, the device internal gain will be changed allowing it to function with a 2.5g, 3.3g, 6.7g, or 10g sensitivity (Table 3). This feature is ideal when a product has applications requiring different sensitivities for optimum performance. The sensitivity can be changed at anytime during the operation of the product. The g-Select1 and gSelect2 pins can be left unconnected for applications requiring only a 2.5g sensitivity as the device has an internal pull-down to keep it at that sensitivity (480 mV/g). Table 3. g-Select pin Descriptions g-Select2 g-Select1 g-Range Sensitivity 0 0 2.5g 480 mV/g 0 1 3.3g 360 mV/g 1 0 6.7g 180 mV/g 1 1 10g 120 mV/g Sleep Mode The 2 axis accelerometer provides a Sleep Mode that is ideal for battery operated products. When Sleep Mode is active, the device outputs are turned off, providing significant reduction of operating current. A low input signal on pin 12 (Sleep Mode) will place the device in this mode and reduce the current to 3 µA typ. For lower power consumption, it is recommended to set g-Select1 and g-Select2 to 2.5g mode. By placing a high input signal on pin 12, the device will resume to normal mode of operation. Filtering The 2 axis accelerometer contains onboard single-pole switched capacitor filters. Because the filter is realized using switched capacitor techniques, there is no requirement for external passive components (resistors and capacitors) to set the cut-off frequency. Figure 3. Simplified Transducer Physical Model Ratiometricity Ratiometricity simply means the output offset voltage and sensitivity will scale linearly with applied supply voltage. That is, as supply voltage is increased, the sensitivity and offset increase linearly; as supply voltage decreases, offset and sensitivity decrease linearly. This is a key feature when interfacing to a microcontroller or an A/D converter because it provides system level cancellation of supply induced errors in the analog to digital conversion process. MMA6281QT 4 Sensors Freescale Semiconductor BASIC CONNECTIONS Pin Descriptions Connection Diagram ZOUT PCB Layout POWER SUPPLY g-Select2 2 11 N/C VDD 3 10 N/C VSS 4 9 N/C 5 6 7 8 N/C Sleep Mode N/C 12 N/C 1 N/C g-Select1 Figure 4. Pinout Description Table 4. Pin Descriptions Pin No. Pin Name 1 g-Select1 Logic input pin to select g level. 2 g-Select2 Logic input pin to select g level. 3 VDD Power Supply Input 4 VSS Power Supply Ground 5-7 N/C No internal connection. Leave unconnected. 8 - 11 N/C Unused for factory trim. Leave unconnected. 12 Sleep Mode 13 ZOUT Z direction output voltage. 14 N/C No internal connection. Leave unconnected. 15 XOUT 16 N/C Logic Inputs Logic input pin to enable product or Sleep Mode. No internal connection. Leave unconnected. g-Select1 ZOUT 13 1 kΩ 0.1 µF 2 g-Select2 VDD MMA6281QT 3 12 C C g-Select1 VRH VDD P0 VSS P1 g-Select2 P2 XOUT R ZOUT R C C A/DIN C A/DIN Figure 6. Recommended PCB Layout for Interfacing Accelerometer to Microcontroller NOTES: 1. Use 0.1 µF capacitor on VDD to decouple the power source. Do not exceed capacitor values of 2.2 or 3.3 µF. Slow dV/dt rise times on VDD may cause the device to not power up below 0°C.To ensure operation below 0°C ensure VDD line has the ability to reach 2.2V in < 0.1 ms as measured on the device at the VDD pin. If output signal does not assert itself, then the dv/dt at the VDD pin of the device should be measured. 2. Physical coupling distance of the accelerometer to the microcontroller should be minimal. 3. The flag underneath the package is internally connected to ground. It is not recommended for the flag to be soldered down. 4. Place a ground plane beneath the accelerometer to reduce noise, the ground plane should be attached to all of the open ended terminals shown in Figure 6. 5. Use an RC filter with 1.0 kΩ and 0.1 µF on the outputs of the accelerometer to minimize clock noise (from the switched capacitor filter circuit). 6. PCB layout of power and ground should not couple power supply noise. VDD 7. Accelerometer and microcontroller should not be a high current path. 0.1 µF 4 VSS Sleep Mode Description X direction output voltage. 1 VDD Microcontroller 14 13 Accelerometer 16 15 N/C N/C XOUT Top View VSS XOUT Sleep Mode Logic Input 15 1 kΩ 0.1 µF Figure 5. Accelerometer with Recommended 8. A/D sampling rate and any external power supply switching frequency should be selected such that they do not interfere with the internal accelerometer sampling frequency (11 kHz for the sampling frequency). This will prevent aliasing errors. 9. PCB layout should not run traces or vias under the QFN part. This could lead to ground shorting to the accelerometer flag. MMA6281QT Sensors Freescale Semiconductor 5 DYNAMIC ACCELERATION Top View Top View Side View 14 13 1 12 2 11 3 10 4 9 5 6 7 -X -Z Bottom +X 15 Top 16 +Z 8 : Arrow indicates direction of mass movement. 16-Pin QFN Package STATIC ACCELERATION In 2.5g mode Direction of Earth’s gravity field.* Top View Side View XOUT@ 0g = 1.65 V ZOUT @ 0g = 1.65 V XOUT @ 0g = 1.65 V ZOUT @ +1g = 2.13 V XOUT @ -1g = 1.17 V ZOUT @ 0g = 1.65 V XOUT @ +1g = 2.13 V ZOUT @ 0g = 1.65 V XOUT @ 0g = 1.65 V ZOUT @ -1g = 1.17 V XOUT @ 0g = 1.65 V ZOUT @ 0g = 1.65 V * When positioned as shown, the Earth’s gravity will result in a positive 1g output. MMA6281QT 6 Sensors Freescale Semiconductor MINIMUM RECOMMENDED FOOTPRINT FOR SURFACE MOUNTED APPLICATIONS Surface mount board layout is a critical portion of the total design. The footprint for the surface mount packages must be the correct size to ensure proper solder connection interface between the board and the package. With the correct footprint, the packages will self-align when subjected to a solder reflow process. It is always recommended to design boards with a solder mask layer to avoid bridging and shorting between solder pads. The flag underneath the package is internally connected to ground. It is not recommended for the flag to be soldered down. • Do not solder down flag for consumer application • Do not place metal pattern or via structures underneath of package PCB DESIGN GUIDELINES The following are the recommended guidelines to follow for mounting QFN sensors for either automotive or consumer applications. 1. NSMD (Non Solder Mask Defined) is shown in Figure 7. 2. Solder mask opening = PCB land pad +0.1 mm. 3. Stencil aperture size = PCB land pad – 0.025mm, as shown in Figure 8 with a 6 mil stencil. 4. Do not place insertion components or vias at a distance less than 2mm from the package land area. 5. Signal trace connected to pads should be as symmetric as possible. Put dummy traces if there is NC pads, in order to have same length of exposed trace for all pads. Signal traces with 0.1mm width and 6. 7. 8. 9. min. 0.5mm length for all PCB land pad near package are recommended as shown in Figure 7 and Figure 8. Wider trace can be continued after the 0.5mm zone. Use a standard pick and place process and equipment (no hand soldering process). It is recommended to use a cleanable solder paste with an additional cleaning step after SMT mount It is recommended to avoid screwing down the PCB to fix it into an enclosure since this may cause the PCB to bend. PC boards should be rated for multiple reflow of leadfree conditions with 260°C maximum temperature. \ PCB land pattern - NSMD Package Pad Signal trace 0.1mm width and 0.5mm (min) length near package. Wider trace can be continued after these traces. 0.50 mm 0.55 mm Cu: 0.55 x 0.50 mm sq. Solder mask opening = PCB land pad +0.1mm =0.65x0.60 mm sq. Figure 7. NSMD Solder Mask Design Guidelines MMA6281QT Sensors Freescale Semiconductor 7 Signal trace near package: 0.1mm width and 0.5mm (min) length are recommended near package. Wider trace can be continued after these. Stencil opening (black) for land pad (yellow) = PCB landing pad -0.025mm = 0.525mmx0,475mm Package foot pirnt Figure 8. Stencil Design Guidelines MMA6281QT 8 Sensors Freescale Semiconductor PACKAGE DIMENSIONS PAGE 1 OF 3 CASE 1622-02 ISSUE B 16-LEAD QFN MMA6281QT Sensors Freescale Semiconductor 9 PACKAGE DIMENSIONS PAGE 2 OF 3 CASE 1622-02 ISSUE B 16-LEAD QFN MMA6281QT 10 Sensors Freescale Semiconductor PACKAGE DIMENSIONS PAGE 3 OF 3 CASE 1622-02 ISSUE B 16-LEAD QFN MMA6281QT Sensors Freescale Semiconductor 11 How to Reach Us: Home Page: www.freescale.com Web Support: http://www.freescale.com/support USA/Europe or Locations Not Listed: Freescale Semiconductor, Inc. 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