MMA6281QT

Freescale Semiconductor Technical Data Document Number: MMA6281QT Rev 0, 10/2006 ±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 ideal for handheld battery powered electronics. Features • • • • • • • • • • • 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 MMA6281QT MMA6281QT: XZ AXIS ACCELEROMETER ± 2.5g/3.3g/6.7g/10g Bottom View Typical Applications • • • • • • • • 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) ORDERING INFORMATION N/C 16-LEAD QFN CASE 1622-02 Top View XOUT ZOUT 13 12 Sleep Mode 11 N/C 10 N/C 9 N/C 5 N/C 6 N/C 7 N/C 8 N/C Device MMA6281QT MMA6281QR2 Temp. Range – 20 to +85°C – 20 to +85°C Case No. 1622-02 1622-02 Package QFN-16, Tray QFN-16,Tape & Reel g-Select1 1 g-Select2 2 VDD 3 VSS 4 16 15 Figure 1. Pin Connections © Freescale Semiconductor, Inc., 2006. All rights reserved. N/C 14 VDD g-Select1 g-Select2 Oscillator Clock Generator X-Temp Comp XOUT Sleep Mode G-Cell Sensor C to V Converter Gain + Filter Control Logic EEPROM Trim Circuits 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 Maximum Acceleration (all axis) Supply Voltage Drop Test (1) Symbol gmax VDD Ddrop Tstg Value ±2000 –0.3 to +3.6 1.8 –40 to +125 Unit g V m °C 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 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) 2.5g 3.3g 6.7g 10g Sensitivity(4) 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(6) Enable Response Time(7) Sensing Element Resonant Frequency X Z Internal Sampling Frequency Output Stage Performance Full-Scale Output Range (IOUT = 30 µA) Nonlinearity, XOUT, ZOUT Cross-Axis Sensitivity(8) VFSO NLOUT VXZ VSS+0.25 –1.0 — — — — VDD–0.25 +1.0 5.0 V %FSO % fGCELL fGCELL fCLK — — — 6.0 3.4 11 — — — kHz kHz kHz tRESPONSE tENABLE — — 1.0 0.5 2.0 2.0 ms ms nRMS nPSD — — 3.0 350 — — mVrms µg/ Hz f-3dB f-3dB — — 350 150 — — Hz Hz Sensitivity (TA = 25°C, VDD = 3.3 V) S2.5g S3.3g S6.7g S10g S,TA 444 333 167 111 — 480 360 180 120 ±0.03 516 387 193 129 — mV/g mV/g mV/g mV/g %/°C VOFF VOFF, TA 1.485 — 1.65 ±2 1.815 — V mg/°C gFS gFS gFS gFS — — — — ±2.5 ±3.3 ±6.7 ±10.0 — — — — g g g g VDD IDD IDD TA 2.2 — — –20 3.3 500 3 — 3.6 800 10 +85 V µA µA °C Symbol Min Typ Max Unit 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. The response time between 10% of full scale Vdd input voltage and 90% of the final operating output voltage. 7. The response time between 10% of full scale Sleep Mode input voltage and 90% of the final operating output voltage. 8. 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 0 0 1 1 g-Select1 0 1 0 1 g-Range 2.5g 3.3g 6.7g 10g Sensitivity 480 mV/g 360 mV/g 180 mV/g 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 Top View XOUT ZOUT N/C N/C PCB Layout POWER SUPPLY 16 15 g-Select1 g-Select2 VDD VSS 1 2 3 4 5 N/C 6 N/C 14 13 12 11 10 9 7 N/C 8 N/C Sleep Mode N/C Accelerometer N/C N/C VDD VSS Sleep Mode g-Select1 g-Select2 XOUT R C R C C VRH P0 P1 P2 A/DIN Microcontroller VDD VSS C Figure 4. Pinout Description Table 4. Pin Descriptions Pin No. 1 2 3 4 5-7 8 - 11 12 13 14 15 16 Pin Name g-Select1 g-Select2 VDD VSS N/C N/C Sleep Mode ZOUT N/C XOUT N/C Description Logic input pin to select g level. Logic input pin to select g level. Power Supply Input Power Supply Ground No internal connection. Leave unconnected. Unused for factory trim. Leave unconnected. Logic input pin to enable product or Sleep Mode. Z direction output voltage. No internal connection. Leave unconnected. X direction output voltage. No internal connection. Leave unconnected. ZOUT 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 on VDD-GND. 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. 7. Accelerometer and microcontroller should not be a high current path. 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. Logic Inputs 1 g-Select1 ZOUT 13 1 kΩ 0.1 µF VDD 2 g-Select2 MMA6281QT 3 VDD 0.1 µF 4 VSS XOUT 15 Sleep Mode 1 kΩ 0.1 µF 12 Logic Input Figure 5. Accelerometer with Recommended Connection Diagram MMA6281QT Sensors Freescale Semiconductor 5 DYNAMIC ACCELERATION Top View Top View Side View 16 1 15 14 13 12 Top +X 3 4 5 6 7 8 10 9 -X -Z Bottom 2 11 +Z : Arrow indicates direction of mass movement. 16-Pin QFN Package STATIC ACCELERATION In 2.5g mode Top View Direction of Earth’s gravity field.* Side View XOUT@ 0g = 1.65 V ZOUT @ 0g = 1.65 V XOUT @ 0g = 1.65 V ZOUT @ +1g = 2.13 V XOUT @ +1g = 2.13 V ZOUT @ 0g = 1.65 V XOUT @ -1g = 1.17 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. 6.0 0.55 12 4.25 9 13 6.0 8 1.00 1 4 Flag Solder areas Non-Solder areas 5 0.50 Pin 1 ID (non metallic) 16 MMA6281QT Sensors Freescale Semiconductor 7 PACKAGE DIMENSIONS PAGE 1 OF 3 CASE 1622-02 ISSUE B 16-LEAD QFN MMA6281QT 8 Sensors Freescale Semiconductor PACKAGE DIMENSIONS PAGE 2 OF 3 CASE 1622-02 ISSUE B 16-LEAD QFN MMA6281QT Sensors Freescale Semiconductor 9 PACKAGE DIMENSIONS PAGE 3 OF 3 CASE 1622-02 ISSUE B 16-LEAD QFN MMA6281QT 10 Sensors Freescale Semiconductor How to Reach Us: Home Page: www.freescale.com E-mail: support@freescale.com USA/Europe or Locations Not Listed: Freescale Semiconductor Technical Information Center, CH370 1300 N. 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Freescale™ and the Freescale logo are trademarks of Freescale Semiconductor, Inc. All other product or service names are the property of their respective owners. © Freescale Semiconductor, Inc., 2006. All rights reserved. MMA6281QT Rev. 0 10/2006