Small and Thin ±2 g Accelerometer ADXL322 FEATURES GENERAL DESCRIPTION Small and thin 4 mm × 4 mm × 1.45 mm LFCSP package 2 mg resolution at 60 Hz Wide supply voltage range: 2.4 V to 6 V Low power: 340 μA at VS = 2.4 V (typ) Good zero g bias stability Good sensitivity accuracy X-axis and Y-axis aligned to within 0.1° (typ) BW adjustment with a single capacitor Single-supply operation 10,000 g shock survival Pb Free: Compatible with Sn/Pb and Pb-free solder processes The ADXL322 is a small, thin, low power, complete, dual-axis accelerometer with signal conditioned voltage outputs, which are all on a single monolithic IC. The product measures acceleration with a full-scale range of ±2 g (typical). It can also measure both dynamic acceleration (vibration) and static acceleration (gravity). The ADXL322’s typical noise floor is 220 μg/√Hz, which allows signals below 2 mg to be resolved in tilt-sensing applications using narrow bandwidths (<60 Hz). The user selects the bandwidth of the accelerometer using capacitors CX and CY at the XOUT and YOUT pins. Bandwidths of 0.5 Hz to 2.5 kHz can be selected to suit the application. APPLICATIONS The ADXL322 is available in a 4 mm × 4 mm × 1.45 mm, 16-lead, plastic LFCSP. Cost-sensitive motion- and tilt-sensing applications Smart hand-held devices Mobile phones Sports and health-related devices PC security and PC peripherals FUNCTIONAL BLOCK DIAGRAM +3V VS ADXL322 CDC AC AMP DEMOD OUTPUT AMP OUTPUT AMP SENSOR COM ST RFILT 32kΩ YOUT CY XOUT CX 05589-001 RFILT 32kΩ Figure 1. Rev. 0 Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Trademarks and registered trademarks are the property of their respective owners. One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. www.analog.com Tel: 781.329.4700 Fax: 781.461.3113 © 2005 Analog Devices, Inc. All rights reserved. ADXL322 TABLE OF CONTENTS Specifications..................................................................................... 3 Setting the Bandwidth Using CX and CY ................................. 12 Absolute Maximum Ratings............................................................ 4 Self-Test ....................................................................................... 12 ESD Caution.................................................................................. 4 Design Trade-Offs for Selecting Filter Characteristics: The Noise/BW Trade-Off.................................................................. 12 Pin Configuration and Function Descriptions............................. 5 Typical Performance Characteristics (VS = 3.0 V) ....................... 7 Theory of Operation ...................................................................... 11 Performance ................................................................................ 11 Applications..................................................................................... 12 Use with Operating Voltages Other than 3 V............................. 13 Use as a Dual-Axis Tilt Sensor ................................................. 13 Outline Dimensions ....................................................................... 14 Ordering Guide .......................................................................... 14 Power Supply Decoupling ......................................................... 12 REVISION HISTORY 6/05—Revision 0: Initial Version Rev. 0 | Page 2 of 16 ADXL322 SPECIFICATIONS TA = 25°C, VS = 3 V, CX = CY = 0.1 μF, Acceleration = 0 g, unless otherwise noted 1 . Table 1. Parameter SENSOR INPUT Measurement Range Nonlinearity Package Alignment Error Alignment Error Cross-Axis Sensitivity SENSITIVITY (RATIOMETRIC) 2 Sensitivity at XOUT, YOUT Sensitivity Change due to Temperature 3 ZERO g BIAS LEVEL (RATIOMETRIC) 0 g Voltage at XOUT, YOUT Initial 0 g Bias Deviation from Ideal 0 g Offset Vs. Temperature NOISE PERFORMANCE Noise Density FREQUENCY RESPONSE 4 CX, CY Range 5 RFILT Tolerance Sensor Resonant Frequency SELF-TEST 6 Logic Input Low Logic Input High ST Input Resistance to Ground Output Change at XOUT, YOUT OUTPUT AMPLIFIER Output Swing Low Output Swing High POWER SUPPLY Operating Voltage Range Quiescent Supply Current Turn-On Time 7 TEMPERATURE Operating Temperature Range Conditions Each axis Min Max X sensor to Y sensor Unit g % Degrees Degrees % ±2 ±0.2 ±1 ±0.1 ±2 % of full scale Each axis VS = 3 V VS = 3 V Each axis VS = 3 V Typ 378 420 0.01 462 mV/g %/°C 1.3 1.5 ±50 <±0.5 1.7 V mg mg/°C at 25°C 220 0.002 μg/√Hz rms 32 ± 15% 5.5 10 μF kΩ kHz Self-test 0 to 1 0.6 2.4 50 125 V V kΩ mV No load No load 0.2 2.7 V V T 2.4 6 V mA ms 70 °C 0.45 20 −20 1 All minimum and maximum specifications are guaranteed. Typical specifications are not guaranteed. Sensitivity is essentially ratiometric to VS. For VS = 2.7 V to 3.3 V, sensitivity is 138 mV/V/g to 142 mV/V/g typical. 3 Defined as the output change from ambient-to-maximum temperature or ambient-to-minimum temperature. 4 Actual frequency response controlled by user-supplied external capacitor (CX, CY). 5 Bandwidth = 1/(2 × π × 32 kΩ × C). For CX, CY = 0.002 μF, bandwidth = 2500 Hz. For CX, CY = 10 μF, bandwidth = 0.5 Hz. Minimum/maximum values are not tested. 6 Self-test response changes cubically with VS. 7 Larger values of CX, CY increase turn-on time. Turn-on time is approximately 160 × CX or CY + 4 ms, where CX, CY are in μF. 2 Rev. 0 | Page 3 of 16 ADXL322 ABSOLUTE MAXIMUM RATINGS Table 2. Parameter Acceleration (Any Axis, Unpowered) Acceleration (Any Axis, Powered) VS All Other Pins Output Short-Circuit Duration (Any Pin to Common) Operating Temperature Range Storage Temperature Rating 10,000 g 10,000 g −0.3 V to +7.0 V (COM − 0.3 V) to (VS + 0.3 V) Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. Indefinite −55°C to +125°C −65°C to +150°C ESD CAUTION ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on the human body and test equipment and can discharge without detection. Although this product features proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance degradation or loss of functionality. Rev. 0 | Page 4 of 16 ADXL322 PIN CONFIGURATION AND FUNCTION DESCRIPTIONS NC VS VS NC NC XOUT ST ADXL322 NC COM TOP VIEW (Not to Scale) YOUT NC COM COM COM NC NC = NO CONNECT 05589-022 NC Figure 2. Pin Configuration Table 3. Pin Function Descriptions Mnemonic NC ST COM NC COM COM COM NC NC YOUT NC XOUT NC VS VS NC Description Do Not Connect Self-Test Common Do Not Connect Common Common Common Do Not Connect Do Not Connect Y-Channel Output Do Not Connect X-Channel Output Do Not Connect 2.4 V to 6 V 2.4 V to 6 V Do Not Connect 4.000 0.600 MAX 0.325 0.650 0.650 0.350 MAX 1.950 0.325 4.000 1.950 Figure 3. 4 mm × 4 mm 16- pad LFCSP Recommended Pad Layout Rev. 0 | Page 5 of 16 05589-023 Pin No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 ADXL322 CRITICAL ZONE TL TO TP tP TP TEMPERATURE RAMP-UP TL tL TSMAX TSMIN tS RAMP-DOWN 05589-002 PREHEAT t25°C TO PEAK TIME Figure 4. Recommended Soldering Profile Table 4. Recommended Soldering Profile Profile Feature Average Ramp Rate (TL to TP) Preheat Minimum Temperature (TSMIN) Minimum Temperature (TSMAX) Time (TSMIN to TSMAX), tS TSMAX to TL Ramp-Up Rate Time Maintained Above Liquidous (TL) Liquidous Temperature (TL) Time (tL) Peak Temperature (TP) Time within 5°C of Actual Peak Temperature (tP) Ramp-Down Rate Time 25°C to Peak Temperature Rev. 0 | Page 6 of 16 Sn63/Pb37 3°C/sec max Pb-Free 3°C/sec max 100°C 150°C 60 sec − 120 sec 150°C 200°C 60 sec − 150 sec 3°C/sec 3°C/sec 183°C 60 sec − 150 sec 240°C + 0°C/−5°C 10 sec − 30 sec 6°C/sec max 6 min max 217°C 60 sec − 150 sec 260°C + 0°C/−5°C 20 sec − 40 sec 6°C/sec max 8 min max ADXL322 TYPICAL PERFORMANCE CHARACTERISTICS (VS = 3.0 V) 35 40 30 35 30 % OF POPULATION 20 15 10 25 20 15 10 0 05589-007 5 05589-004 5 0 1.40 1.42 1.44 1.46 1.48 1.50 1.52 1.54 1.56 1.58 1.60 1.40 1.42 1.44 1.46 1.48 1.50 1.52 1.54 1.56 1.58 1.60 OUTPUT (V) OUTPUT (V) Figure 5. X-Axis Zero g Bias at 25°C Figure 8. Y-Axis Zero g Bias at 25°C 40 45 35 40 35 % OF POPULATION 25 20 15 10 30 25 20 15 10 05589-005 5 0 –2.0 –1.5 –1.0 –0.5 0 0.5 1.0 1.5 5 0 2.0 –2.0 –1.5 –1.0 –0.5 0 0.5 1.0 1.5 2.0 TEMPERATURE COEFFICIENT (mg/°C) TEMPERATURE COEFFICIENT (mg/°C) Figure 6. X-Axis Zero g Bias Temperature Coefficient Figure 9. Y-Axis Zero g Bias Temperature Coefficient 50 45 45 40 40 35 % OF POPULATION 35 30 25 20 15 30 25 20 15 10 10 5 0 0.400 0.405 0.410 0.415 0.420 0.425 0.430 0.435 0.440 0.445 0.450 05589-006 % OF POPULATION 05589-008 % OF POPULATION 30 5 0 0.400 0.405 0.410 0.415 0.420 0.425 0.430 0.435 0.440 0.445 0.450 SENSITIVITY (V/g) SENSITIVITY (V/g) Figure 7. X-Axis Sensitivity at 25°C Figure 10. Y-Axis Sensitivity at 25°C Rev. 0 | Page 7 of 16 05589-009 % OF POPULATION 25 0.440 1.575 0.435 1.550 0.430 1.525 1.500 1.475 0.425 0.420 0.415 1.450 0.410 1.425 0.405 1.400 –40 –20 0 20 40 60 0.400 –40 80 05589-013 SENSITIVITY V/g 1.600 05589-010 0g OUTPUT (V) ADXL322 –20 0 20 40 60 80 TEMPERATURE (°C) TEMPERATURE (°C) Figure 11. Zero g Bias vs. Temperature—Parts Soldered to PCB Figure 14. Sensitivity vs. Temperature—Parts Soldered to PCB 70 45 40 60 35 % OF POPULATION % OF POPULATION 50 40 30 20 30 25 20 15 05589-012 0 150 160 170 180 190 200 210 220 230 240 05589-015 10 10 5 0 250 150 160 170 180 NOISE μg/ Hz 200 210 220 230 240 250 4 5 NOISE μg/ Hz Figure 12. X-Axis Noise Density at 25°C Figure 15. Y-Axis Noise Density at 25°C 25 30 25 % OF POPULATION 20 15 10 5 20 15 10 0 –5 –4 –3 –2 –1 0 1 2 3 4 05589-014 5 05589-011 % OF POPULATION 190 0 5 –5 PERCENT SENSITIVITY (%) –4 –3 –2 –1 0 1 2 3 PERCENT SENSITIVITY (%) Figure 13. Z vs. X Cross-Axis Sensitivity Figure 16. Z vs. Y Cross-Axis Sensitivity Rev. 0 | Page 8 of 16 25 25 20 20 % OF POPULATION 15 10 10 5 05589-016 5 15 0 0.08 0.09 0.10 0.11 0.12 0.13 0.14 0.15 05589-019 % OF POPULATION ADXL322 0 0.16 0.08 0.09 0.10 SELF-TEST (V) 0.11 0.12 0.13 0.14 0.15 0.16 SELF-TEST (V) Figure 17. X-Axis Self-Test Response at 25°C Figure 19. Y-Axis Self-Test Response at 25°C 60 40 30 20 10 0 370 390 410 430 450 470 490 CURRENT (μA) Figure 18. Supply Current at 25°C Figure 20. Turn-On Time—CX, CY = 0.1 μF, Time Scale = 2 ms/DIV 550 500 CURRENT (μA) 450 400 350 300 –40 05589-021 350 05589-020 05589-017 % OF POPULATION 50 –20 0 20 40 60 80 100 TEMPERATURE (°C) Figure 21. Supply Current vs. Temperature VS=3V Rev. 0 | Page 9 of 16 120 ADXL322 XL 322J #1234 5678P YOUT = 1.50V XOUT = 1.50V YOUT = 1.08V XOUT = 1.92V YOUT = 1.50V XOUT = 1.500V YOUT = 1.500V EARTH'S SURFACE Figure 22. Output Response vs. Orientation Rev. 0 | Page 10 of 16 05589-018 YOUT = 1.92V XOUT = 1.08V XL 322J #1234 5678P XOUT = 1.50V XL 322J #1234 5678P XL 322J #1234 5678P ADXL322 THEORY OF OPERATION The ADXL322 is a complete acceleration measurement system on a single monolithic IC. The ADXL322 has a measurement range of ±2 g. It contains a polysilicon surface micromachined sensor and signal conditioning circuitry to implement an openloop acceleration measurement architecture. The output signals are analog voltages that are proportional to acceleration. The accelerometer measures static acceleration forces, such as gravity, which allows it to be used as a tilt sensor. The sensor is a polysilicon surface-micromachined structure built on top of a silicon wafer. Polysilicon springs suspend the structure over the surface of the wafer and provide a resistance against acceleration forces. Deflection of the structure is measured using a differential capacitor that consists of independent fixed plates and plates attached to the moving mass. The fixed plates are driven by 180° out-of-phase square waves. Acceleration deflects the beam and unbalances the differential capacitor, resulting in an output square wave whose amplitude is proportional to acceleration. Phase-sensitive demodulation techniques are then used to rectify the signal and determine the direction of the acceleration. PERFORMANCE Rather than using additional temperature compensation circuitry, innovative design techniques were used to ensure built-in high performance. As a result, there is neither quantization error nor nonmonotonic behavior, and temperature hysteresis is very low (typically less than 5 mg over the −20°C to +70°C temperature range). Figure 11 shows the zero g output performance of eight parts (X- and Y-axis) over a −20°C to +70°C temperature range. Figure 14 demonstrates the typical sensitivity shift over temperature for supply voltages of 3 V. This is typically better than ±1% over the −20°C to +70°C temperature range. The demodulator’s output is amplified and brought offchip through a 32 kΩ resistor. The user then sets the signal bandwidth of the device by adding a capacitor. This filtering improves measurement resolution and helps prevent aliasing. Rev. 0 | Page 11 of 16 ADXL322 APPLICATIONS POWER SUPPLY DECOUPLING For most applications, a single 0.1 μF capacitor, CDC, adequately decouples the accelerometer from noise on the power supply. However, in some cases, particularly where noise is present at the 140 kHz internal clock frequency (or any harmonic thereof), noise on the supply can cause interference on the ADXL322 output. If additional decoupling is needed, a 100 Ω (or smaller) resistor or ferrite bead can be inserted in the supply line. Additionally, a larger bulk bypass capacitor (in the 1 μF to 4.7 μF range) can be added in parallel to CDC. SETTING THE BANDWIDTH USING CX AND CY The ADXL322 has provisions for band-limiting the XOUT and YOUT pins. Capacitors must be added at these pins to implement low-pass filtering for antialiasing and noise reduction. The equation for the 3 dB bandwidth is F−3 dB = 1/(2π(32 kΩ) × C(X, Y)) or more simply, F–3 dB = 5 μF/C(X, Y) The tolerance of the internal resistor (RFILT) typically varies as much as ±15% of its nominal value (32 kΩ), and the bandwidth varies accordingly. A minimum capacitance of 2000 pF for CX and CY is required in all cases. DESIGN TRADE-OFFS FOR SELECTING FILTER CHARACTERISTICS: THE NOISE/BW TRADE-OFF The accelerometer bandwidth selected ultimately determines the measurement resolution (smallest detectable acceleration). Filtering can be used to lower the noise floor, which improves the resolution of the accelerometer. Resolution is dependent on the analog filter bandwidth at XOUT and YOUT. The output of the ADXL322 has a typical bandwidth of 2.5 kHz. To limit aliasing errors, the user must filter the signal at this point. The analog bandwidth must be no more than half the A/D sampling frequency to minimize aliasing. The analog bandwidth can be further decreased to reduce noise and improve resolution. The ADXL322 noise has the characteristics of white Gaussian noise, which contributes equally at all frequencies and is described in terms of μg/√Hz (the noise is proportional to the square root of the accelerometer’s bandwidth). The user should limit bandwidth to the lowest frequency needed by the application in order to maximize the resolution and dynamic range of the accelerometer. With the single-pole, roll-off characteristic, the typical noise of the ADXL322 is determined by rmsNoise = (220 μg/ Hz ) × ( BW × 1.6 ) Table 5. Filter Capacitor Selection, CX and CY Bandwidth (Hz) 1 10 50 100 200 500 At 100 Hz bandwidth the noise will be Capacitor (μF) 4.7 0.47 0.10 0.05 0.027 0.01 rmsNoise = (220 μg/ Hz ) × ( 100 × 1.6 ) = 2.8 mg Often, the peak value of the noise is desired. Peak-to-peak noise can only be estimated by statistical methods. Table 6 is useful for estimating the probabilities of exceeding various peak values, given the rms value. Table 6. Estimation of Peak-to-Peak Noise SELF-TEST The ST pin controls the self-test feature. When this pin is set to VS, an electrostatic force is exerted on the accelerometer beam. The resulting movement of the beam allows the user to test if the accelerometer is functional. The typical change in output is 300 mg (corresponding to 125 mV). This pin can be left opencircuit or connected to common (COM) in normal use. Peak-to-Peak Value 2 × rms 4 × rms 6 × rms 8 × rms The ST pin should never be exposed to voltages greater than VS + 0.3 V. If this cannot be guaranteed due to the system design (for instance, if there are multiple supply voltages), then a low VF clamping diode between ST and VS is recommended. Rev. 0 | Page 12 of 16 % of Time That Noise Exceeds Nominal Peak-to-Peak Value 32 4.6 0.27 0.006 ADXL322 Peak-to-peak noise values give the best estimate of the uncertainty in a single measurement. Table 7 gives the typical noise output of the ADXL322 for various CX and CY values. Table 7. Filter Capacitor Selection (CX, CY) Bandwidth (Hz) 10 50 100 500 CX, CY (μF) 0.47 0.1 0.047 0.01 RMS Noise (mg) 0.9 2 2.8 6.2 Peak-to-Peak Noise Estimate (mg) 5.3 11.8 16.7 37.3 USE WITH OPERATING VOLTAGES OTHER THAN 3 V The ADXL322 is tested and specified at VS = 3 V; however, this part can be powered with VS as low as 2.4 V or as high as 6 V. Note that some performance parameters change as the supply voltage is varied. The ADXL322 output is ratiometric, so the output sensitivity (or scale factor) varies proportionally to supply voltage. At VS = 5 V, the output sensitivity is typically 750 mV/g. At VS = 2.4 V, the output sensitivity is typically 335 mV/g. The zero g bias output is also ratiometric, so the zero g output is nominally equal to VS/2 at all supply voltages. The output noise is not ratiometric but is absolute in volts; therefore, the noise density decreases as the supply voltage increases. This is because the scale factor (mV/g) increases while the noise voltage remains constant. At VS = 5 V, the noise density is typically 150 μg/√Hz, while at VS = 2.4 V, the noise density is typically 300 μg/√Hz, USE AS A DUAL-AXIS TILT SENSOR Tilt measurement is one of the ADXL322’s most popular applications. An accelerometer uses the force of gravity as an input vector to determine the orientation of an object in space. An accelerometer is most sensitive to tilt when its sensitive axis is perpendicular to the force of gravity (that is, when the package is parallel to the earth’s surface). At this orientation, the accelerometer’s sensitivity to changes in tilt is highest. When the accelerometer is oriented on axis to gravity (near its +1 g or −1 g reading), the change in output acceleration per degree of tilt is negligible. When the accelerometer is perpendicular to gravity, its output changes nearly 17.5 mg per degree of tilt. At 45°, its output changes at only 12.2 mg per degree of tilt, and resolution declines. Converting Acceleration to Tilt When the accelerometer is oriented so both its X-axis and Y-axis are parallel to the earth’s surface, it can be used as a 2-axis tilt sensor with both a roll axis and a pitch axis. Once the output signal from the accelerometer has been converted to an acceleration that varies between −1 g and +1 g, the output tilt in degrees is calculated as PITCH = ASIN(AX/1 g) ROLL = ASIN(AY/1 g) Be sure to account for overranges. It is possible for the accelerometers to output a signal greater than ±1 g due to vibration, shock, or other accelerations. Self-test response in g is roughly proportional to the square of the supply voltage. However, when ratiometricity of sensitivity is factored in with supply voltage, the self-test response in volts is roughly proportional to the cube of the supply voltage. For example, at VS = 5 V, the self-test response for the ADXL322 is approximately 610 mV. At VS = 2.4 V, the self-test response is approximately 59 mV. The supply current decreases as the supply voltage decreases. Typical current consumption at VS = 5 V is 700 μA, and typical current consumption at VS = 2.4 V is 340 μA. Rev. 0 | Page 13 of 16 ADXL322 OUTLINE DIMENSIONS 0.20 MIN PIN 1 INDICATOR 0.20 MIN 13 PIN 1 INDICATOR 4.15 4.00 SQ 3.85 0.65 BSC TOP VIEW 16 1 12 2.43 1.75 SQ 1.08 BOTTOM VIEW 9 4 8 0.55 0.50 0.45 5 1.95 BSC 0.05 MAX 0.02 NOM 1.50 1.45 1.40 SEATING PLANE 0.35 0.30 0.25 COPLANARITY 0.05 Figure 23. 16-Lead Lead Frame Chip Scale Package [LFCSP_LQ] 4 mm × 4 mm Body, Thick Quad (CP-16-5) Dimensions shown in millimeters ORDERING GUIDE Model ADXL322JCP 1 ADXL322JCP–REEL1 ADXL322EB 1 Measurement Range ±2 g ±2 g Specified Voltage (V) 3 3 Temperature Range −20°C to +70°C −20°C to +70°C Lead finish—Matte tin. Rev. 0 | Page 14 of 16 Package Description 16-Lead LFCSP_LQ 16-Lead LFCSP_LQ Evaluation Board Package Option CP-16-5 CP-16-5 ADXL322 NOTES Rev. 0 | Page 15 of 16 ADXL322 NOTES © 2005 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D05589–0–6/05(0) Rev. 0 | Page 16 of 16