Freescale Semiconductor Technical Data Document Number: MMA1211D Rev 5, 05/2006 Surface Mount Micromachined Accelerometer MMA1211 The MMA series of silicon capacitive, micromachined accelerometers feature signal conditioning, a 4-pole low pass filter and temperature compensation. Zero-g offset full scale span and filter cut-off are factory set and require no external devices. A full system self-test capability verifies system functionality. Features • • • • • • • • Integral Signal Conditioning Linear Output Ratiometric Performance 4th Order Bessel Filter Preserves Pulse Shape Integrity Calibrated Self-test Low Voltage Detect, Clock Monitor, and EPROM Parity Check Status Transducer Hermetically Sealed at Wafer Level for Superior Reliability Robust Design, High Shocks Survivability MMA1211D: Z AXIS SENSITIVITY MICROMACHINED ACCELEROMETER ±150g Typical Applications • Vibration Monitoring and Recording • Impact Monitoring D SUFFIX EG SUFFIX (Pb-FREE) 16-LEAD SOIC CASE 475-01 ORDERING INFORMATION Device Name Temperature Range Case No. Package MMA1211D –40° to 125°C 475-01 SOIC-16 MMA1211DR2 –40° to 125°C 475-01 SOIC16, Tape & Reel MMA1211EG –40° to 125°C 475-01 SOIC-16 MMA1211EGR2 –40° to 125°C 475-01 SOIC16, Tape & Reel VDD G-Cell Sensor ST Self-test Integrator Gain Control Logic & EPROM Trim Circuits Filter Oscillator Temp Comp Clock Generator VOUT VSS N/C N/C N/C ST VOUT STATUS VSS VDD 1 2 3 4 5 6 7 8 16 15 14 13 12 11 10 9 N/C N/C N/C N/C N/C N/C N/C N/C STATUS Figure 1. Simplified Accelerometer Functional Block Diagram © Freescale Semiconductor, Inc., 2006. All rights reserved. Figure 2. Pin Connections Table 1. Maximum Ratings (Maximum ratings are the limits to which the device can be exposed without causing permanent damage.) Rating Symbol Value Unit Powered Acceleration (all axes) Gpd 1500 g Unpowered Acceleration (all axes) Gupd 2000 g Supply Voltage VDD –0.3 to +7.0 V Ddrop 1.2 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 accelerometers contain internal 2 kV 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. MMA1211D 2 Sensors Freescale Semiconductor Table 2. Operating Characteristics (Unless otherwise noted: –40°C ≤ TA ≤ +105°C, 4.75 ≤ VDD ≤ 5.25, Acceleration = 0g, Loaded output.(1)) Characteristic Symbol Min Typ Max Unit VDD IDD TA gFS 4.75 3.0 –40 — 5.00 — — 169 5.25 6.0 +125 — V mA °C g VOFF VOFF,V S SV f–3dB NLOUT 2.35 0.46 VDD 12.66 2.480 360 –2.0 2.5 0.50 VDD 13.33 2.667 400 — 2.65 0.54 VDD 14.00 2.853 440 2.0 V V mV/g mV/g/V Hz % FSO nRMS nPSD nCLK — — — — 110 2.0 2.8 — — mVrms µV/(Hz1/2) mVpk Self-Test Output Response Input Low Input High Input Loading(7) Response Time(8) gST VIL VIH IIN tST 55 VSS 0.7 × VDD -30 — 75 — — –100 2.0 95 0.3 × VDD VDD –260 10 g V V µA ms Status(9), (10) Output Low (Iload = 100 µA) Output High (Iload = 100 µA) VOL VOH — VDD –0.8 — — 0.4 — V V Minimum Supply Voltage (LVD Trip) VLVD 2.7 3.25 4.0 V fmin 50 — 260 kHz Output Stage Performance Electrical Saturation Recovery Time(11) Full Scale Output Range (IOUT = 200 µA) Capacitive Load Drive(12) Output Impedance tDELAY VFSO CL ZO — 0.25 — — 0.2 — — 300 — VDD–0.25 100 — ms V pF Ω Mechanical Characteristics Transverse Sensitivity(13) Package Resonance VXZ,YZ fPKG — — — 10 5.0 — % FSO kHz Operating Range(2) Supply Voltage(3) Supply Current Operating Temperature Range Acceleration Range Output Signal Zero g (TA = 25°C, VDD = 5.0 V)(4) Zero g Sensitivity (TA = 25°C, VDD = 5.0 V)(5) Sensitivity Bandwidth Response Nonlinearity Noise RMS (0.1-1 kHz) Power Spectral Density Clock Noise (without RC load on output)(6) Clock Monitor Fail Detection Frequency 1. For a loaded output the measurements are observed after an RC filter consisting of a 1 kΩ resistor and a 0.01 µF capacitor to ground. 2. These limits define the range of operation for which the part will meet specification. 3. Within the supply range of 4.75 and 5.25 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. The device can measure both + and – acceleration. With no input acceleration the output is at mid supply. For positive acceleration the output will increase above VDD/2 and for negative acceleration the output will decrease below VDD/2. 5. The device is calibrated at 35g. 6. At clock frequency ≅70 kHz. 7. The digital input pin has an internal pull-down current source to prevent inadvertent self test initiation due to external board level leakages. 8. Time for the output to reach 90% of its final value after a self-test is initiated. 9. The Status pin output is not valid following power-up until at least one rising edge has been applied to the self-test pin. The Status pin is high whenever the self-test input is high, as a means to check the connectivity of the self-test and Status pins in the application. 10. The Status pin output latches high if a Low Voltage Detection or Clock Frequency failure occurs, or the EPROM parity changes to odd. The Status pin can be reset low if the self-test pin is pulsed with a high input for at least 100 µs, unless a fault condition continues to exist. 11. Time for amplifiers to recover after an acceleration signal causes them to saturate. 12. Preserves phase margin (60°) to guarantee output amplifier stability. 13. A measure of the device's ability to reject an acceleration applied 90° from the true axis of sensitivity. MMA1211D Sensors Freescale Semiconductor 3 PRINCIPLE OF OPERATION The Freescale accelerometer is a surface-micromachined integrated-circuit accelerometer. The device consists of a surface micromachined capacitive sensing cell (g-cell) and a CMOS signal conditioning ASIC contained in a single integrated circuit package. The sensing element is sealed hermetically at the wafer level using a bulk micromachined “cap'' wafer. The g-cell is a mechanical structure formed from semiconductor materials (poly silicon) using semiconductor processes (masking and etching). It can be modeled as two stationary plates with a moveable plate in-between. The center plate can be deflected from its rest position by subjecting the system to an acceleration (Figure 3). When the center plate deflects, the distance from it to one fixed plate will increase by the same amount that the distance to the other plate decreases. The change in distance is a measure of acceleration. The g-cell plates form two back-to-back capacitors (Figure 4). As the center plate moves with acceleration, the distance between the plates changes and each capacitor's value will change, (C = Aε/D). Where A is the area of the plate, ε is the dielectric constant, and D is the distance between the plates. The CMOS 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 Figure 3. Transducer Physical Model Figure 4. Equivalent Circuit Model SPECIAL FEATURES Filtering The Freescale accelerometers contain an on board 4-pole switched capacitor filter. A Bessel implementation is used because it provides a maximally flat delay response (linear phase) thus preserving pulse shape integrity. 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. Self-Test The sensor provides a self-test feature that allows the verification of the mechanical and electrical integrity of the accelerometer at any time before or after installation. This feature is critical in applications such as automotive air bag systems where system integrity must be ensured over the life of the vehicle. A fourth “plate'' is used in the g-cell as a selftest plate. When the user applies a logic high input to the selftest pin, a calibrated potential is applied across the self-test plate and the moveable plate. The resulting electrostatic force (Fe = 1/2 AV2/d2) causes the center plate to deflect. The resultant deflection is measured by the accelerometer's control ASIC and a proportional output voltage results. This procedure assures that both the mechanical (g-cell) and electronic sections of the accelerometer are functioning. Ratiometricity Ratiometricity simply means that the output offset voltage and sensitivity will scale linearly with applied supply voltage. That is, as you increase supply voltage 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. Status Freescale accelerometers include fault detection circuitry and a fault latch. The Status pin is an output from the fault latch, OR'd with self-test, and is set high whenever one (or more) of the following events occur: • Supply voltage falls below the Low Voltage Detect (LVD) voltage threshold • Clock oscillator falls below the clock monitor minimum frequency • Parity of the EPROM bits becomes odd in number. The fault latch can be reset by a rising edge on the self-test input pin, unless one (or more) of the fault conditions continues to exist. MMA1211D 4 Sensors Freescale Semiconductor BASIC CONNECTIONS 16 15 14 13 12 11 10 9 1 2 3 4 5 6 7 8 N/C N/C N/C N/C N/C N/C N/C N/C STATUS P1 ST P0 Accelerometer N/C N/C N/C ST VOUT STATUS VSS VDD VOUT VSS VDD A/D In R 1 kΩ C 0.01 µF C 0.1 µF Pin Name 1 thru 3 — Leave unconnected 4 ST Logic input pin used to initiate self-test 5 VOUT 6 STATUS 7 VSS The power supply ground 8 VDD The power supply input 9 thru 13 Trim pins 14 thru 16 — Logic Input 4 Description Output voltage of the accelerometer Logic output pin to indicate fault 8 VDD C1 0.1 µF 7 VSS VOUT Figure 6. Recommended PCB Layout for Interfacing Accelerometer to Microcontroller NOTES: 1. Use a 0.1 µF capacitor on VDD to decouple the power source. 4. Use an RC filter of 1 kΩ and 0.01 µF on the output of the accelerometer to minimize clock noise (from the switched capacitor filter circuit). 5. PCB layout of power and ground should not couple power supply noise. 6 5 0.1 µF 3. 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. No internal connection. Leave unconnected ST 0.1 µF 2. Physical coupling distance of the accelerometer to the microcontroller should be minimal. Used for factory trim. Leave unconnected MMA1211D C VDD Power Supply Pin No. VDD VSS VRH C Table 3. Pin Descriptions Microcontroller PCB Layout Pinout Description R1 1 kΩ STATUS 6. Accelerometer and microcontroller should not be a high current path. Output Signal 7. 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. This will prevent aliasing errors. C2 0.01 µF Figure 5. SOIC Accelerometer with Recommended Connection Diagram MMA1211D Sensors Freescale Semiconductor 5 Dynamic Acceleration Sensing Direction +Z Acceleration of the package in the +Z direction (center plate moves in the −Z direction) will result in an increase in the output. −Z Activation of Self test moves the center plate in the −Z direction, resulting in an increase in the output. Side View Static Acceleration Sensing Direction Direction of Earth's gravity field(1) Side View 1. When positioned as shown, the Earth's gravity will result in a positive 1g output. MMA1211D 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 0.380 in. 9.65 mm 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. 0.050 in. 1.27 mm 0.024 in. 0.610 mm 0.080 in. 2.03 mm Figure 7. Footprint SOIC-16 (Case 475-01) MMA1211D Sensors Freescale Semiconductor 7 PACKAGE DIMENSIONS PAGE 1 OF 2 CASE 475-01 ISSUE C 16 LEAD SOIC MMA1211 8 Sensors Freescale Semiconductor PACKAGE DIMENSIONS PAGE 2 OF 2 CASE 475-01 ISSUE C 16 LEAD SOIC MMA1211 Sensors Freescale Semiconductor 9 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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