Small and Thin ±18 g Accelerometer ADXL321 FEATURES GENERAL DESCRIPTION Small and thin 4 mm × 4 mm × 1.45 mm LFCSP package 3 mg resolution at 50 Hz Wide supply voltage range: 2.4 V to 6 V Low power: 350 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 Compatible with Sn/Pb and Pb-free solder processes The ADXL321 is a small and thin, low power, complete dualaxis accelerometer with signal conditioned voltage outputs, which is all on a single monolithic IC. The product measures acceleration with a full-scale range of ±18 g (typical). It can also measure both dynamic acceleration (vibration) and static acceleration (gravity). The ADXL321’s typical noise floor is 320 µg/√Hz, allowing signals below 3 mg to be resolved in tilt-sensing applications using narrow bandwidths (<50 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 may be selected to suit the application. APPLICATIONS The ADXL321 is available in a very thin 4 mm × 4 mm × 1.45 mm, 16-lead, plastic LFCSP. Vibration monitoring and compensation Abuse event detection Sports equipment FUNCTIONAL BLOCK DIAGRAM +3V VS ADXL321 CDC AC AMP DEMOD OUTPUT AMP OUTPUT AMP SENSOR COM ST RFILT 32kΩ YOUT CY XOUT CX 05291-001 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. Tel: 781.329.4700 www.analog.com Fax: 781.326.8703 © 2004 Analog Devices, Inc. All rights reserved. ADXL321 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 12/04—Revision 0: Initial Version Rev. 0 | Page 2 of 16 ADXL321 SPECIFICATIONS1 TA = 25°C, VS = 3 V, CX = CY = 0.1 µF, Acceleration = 0 g, unless otherwise noted. 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 Temperature3 ZERO g BIAS LEVEL (RATIOMETRIC) 0 g Voltage at XOUT, YOUT 0 g Offset vs. Temperature NOISE PERFORMANCE Noise Density FREQUENCY RESPONSE4 CX, CY Range5 RFILT Tolerance Sensor Resonant Frequency SELF-TEST6 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 Time7 TEMPERATURE Operating Temperature Range Conditions Each axis Min Max X sensor to Y sensor Unit g % Degrees Degrees % ±18 ±0.2 ±1 ±0.1 ±2 % of full scale Each axis VS = 3 V VS = 3 V Each axis VS = 3 V Typ 51 57 0.01 63 mV/g %/°C 1.4 1.5 ±2 1.6 V mg/°C @ 25°C 320 0.002 µg/√Hz rms 32 ± 15% 5.5 10 µF kΩ kHz Self-test 0 to 1 0.6 2.4 50 18 V V kΩ mV No load No load 0.3 2.6 V V 2.4 6 V mA ms +70 °C 0.49 20 −20 1 All minimum and maximum specifications are guaranteed. Typical specifications are not guaranteed. Sensitivity is essentially ratiometric to VS. 3 Defined as the 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 ADXL321 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) Indefinite −55°C to +125°C −65°C to +150°C 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. 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 ADXL321 PIN CONFIGURATION AND FUNCTION DESCRIPTIONS NC VS VS NC 16 15 14 13 NC 1 ADXL321 COM 3 TOP VIEW (Not to Scale) NC 4 5 6 7 COM COM COM XOUT 11 NC 10 YOUT 9 NC 8 NC NC = NO CONNECT 05291-002 ST 2 12 Figure 2. Pin Configuration Table 3. Pin Function Descriptions Pin No. 1, 4, 8, 9, 11, 13, 16 2 3, 5 to 7 10 12 14, 15 Mnemonic NC ST COM YOUT XOUT VS Description Do Not Connect Self-Test Common Y Channel Output X Channel Output 2.4 V to 6 V Rev. 0 | Page 5 of 16 ADXL321 CRITICAL ZONE TL TO TP tP TP TEMPERATURE RAMP-UP TL tL TSMAX TSMIN tS RAMP-DOWN 05291-003 PREHEAT t25°C TO PEAK TIME Figure 3. 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/s max Pb-Free 3°C/s max 100°C 150°C 60 s − 120 s 150°C 200°C 60 s − 150 s 3°C/s 3°C/s 183°C 60 s − 150 s 240°C + 0°C/−5°C 10 s − 30 s 6°C/s max 6 min max 217°C 60 s − 150 s 260°C + 0°C/−5°C 20 s − 40 s 6°C/s max 8 min max ADXL321 25 25 20 20 % OF POPULATION 15 10 5 15 10 05291-004 5 0 05291-007 % OF POPULATION TYPICAL PERFORMANCE CHARACTERISTICS (VS = 3.0 V) 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 VOLTS VOLTS Figure 7. Y-Axis Zero g Bias at 25°C 25 25 20 20 % OF POPULATION 15 10 10 5 05291-005 5 15 0 –10 –8 –6 –4 –2 0 2 4 6 8 05291-008 % OF POPULATION Figure 4. X-Axis Zero g Bias at 25°C 0 10 –10 –8 –6 –4 –2 Figure 5. X-Axis Zero g Bias Temperature Coefficient 2 4 6 8 10 Figure 8. Y-Axis Zero g Bias Temperature Coefficient 50 45 45 40 40 35 35 % OF POPULATION 50 30 25 20 15 30 25 20 15 10 5 0 52 53 54 55 56 57 58 59 05291-009 10 05291-006 % OF POPULATION 0 mg/°C mg/°C 5 0 60 52 mV/g 53 54 55 56 57 58 mV/g Figure 6. X-Axis Sensitivity at 25°C Figure 9. Y-Axis Sensitivity at 25°C Rev. 0 | Page 7 of 16 59 60 0.060 1.575 0.059 1.550 0.058 1.525 1.500 1.475 0.057 0.056 0.055 1.450 0.054 1.425 0.053 1.400 –30 –20 –10 0 10 20 30 40 50 60 70 05291-013 SENSITIVITY (mV/g) 1.600 05291-010 OUTPUT (SCALE = 56mV/g) ADXL321 0.052 –30 80 –10 10 TEMPERATURE (°C) 50 70 Figure 13. Sensitivity vs. Temperature—Parts Soldered to PCB 30 30 25 25 % OF POPULATION 20 15 10 15 10 5 05291-011 5 20 0 200 220 240 260 280 300 320 05291-014 % OF POPULATION Figure 10. Zero g Bias vs. Temperature—Parts Soldered to PCB 0 340 200 220 240 NOISE DENSITY (µg/ Hz) 260 280 300 320 340 NOISE DENSITY (µg/ Hz) Figure 11. X-Axis Noise Density at 25°C Figure 14. 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 05291-015 5 05291-012 % OF POPULATION 30 TEMPERATURE (°C) 0 –5 5 PERCENT SENSITIVITY (%) –4 –3 –2 –1 0 1 2 3 PERCENT SENSITIVITY (%) Figure 12. Z vs. X Cross-Axis Sensitivity Figure 15. Z vs. Y Cross-Axis Sensitivity Rev. 0 | Page 8 of 16 4 5 ADXL321 16 14 % OF POPULATION 12 10 8 6 05291-016 2 05291-019 4 0 10 11 12 13 14 15 16 17 18 19 20 21 mV Figure 19. Turn-On Time—CX, CY = 0.1 µF, Time Scale = 2 ms/DIV Figure 16. X-Axis Self-Test Response at 25°C 40 35 % OF POPULATION 30 25 20 15 10 05291-017 5 0 420 430 440 450 460 470 480 490 500 510 520 530 CURRENT (µA) Figure 17. Supply Current at 25°C 16 14 10 8 6 4 2 05291-018 % OF POPULATION 12 0 10 11 12 13 14 15 16 17 18 19 20 21 mV Figure 18. Y-Axis Self-Test Response at 25°C Rev. 0 | Page 9 of 16 ADXL321 XL 321J #1234 5678P YOUT = 1.500V XOUT = 1.500V YOUT = 1.443V XOUT = 1.557V YOUT = 1.50V XOUT = 1.500V YOUT = 1.500V EARTH'S SURFACE Figure 20. Output Response vs. Orientation (Top View) Rev. 0 | Page 10 of 16 05291-020 YOUT = 1.557V XOUT = 1.443V XL 321J #1234 5678P XOUT = 1.500V XL 321J #1234 5678P XL 321J #1234 5678P ADXL321 THEORY OF OPERATION The ADXL321 is a complete acceleration measurement system on a single monolithic IC. The ADXL321 has a measurement range of ±18 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. The demodulator’s output is amplified and brought off-chip 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. PERFORMANCE Rather than using additional temperature compensation circuitry, innovative design techniques have been used to ensure high performance is built-in. As a result, there is neither quantization error nor nonmonotonic behavior, and temperature hysteresis is very low (typically less than 10 mg over the −20°C to +70°C temperature range). Figure 10 shows the zero g output performance of eight parts (X- and Y-axis) over a −20°C to +70°C temperature range. Figure 13 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. Rev. 0 | Page 11 of 16 ADXL321 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 may cause interference on the ADXL321 output. If additional decoupling is needed, a 100 Ω (or smaller) resistor or ferrite bead may be inserted in the supply line. Additionally, a larger bulk bypass capacitor (in the 1 µF to 4.7 µF range) may be added in parallel to CDC. SETTING THE BANDWIDTH USING CX AND CY The ADXL321 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 ADXL321 has a typical bandwidth of 2.5 kHz. The user must filter the signal at this point to limit aliasing errors. The analog bandwidth must be no more than half the A/D sampling frequency to minimize aliasing. The analog bandwidth may be further decreased to reduce noise and improve resolution. The ADXL321 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 ADXL321 is determined by rmsNoise = (320 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 = (320 µg/ Hz ) × ( 100 ×1.6 ) = 4 mg Often, the peak value of the noise is desired. Peak-to-peak noise can only be estimated by statistical methods. A factor of 6 is generally used to convert rms to peak-to-peak. Table 6 is useful for estimating the probabilities of exceeding various peak values, given the rms value. SELF-TEST Table 6. Estimation of Peak-to-Peak Noise 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 315 mg (corresponding to 18 mV). This pin may 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 ADXL321 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 ADXL321 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) 1.3 2.9 4 9.1 Peak-to-Peak Noise Estimate (mg) 7.8 17.4 24 54.6 USE WITH OPERATING VOLTAGES OTHER THAN 3 V The ADXL321 is tested and specified at VS = 3 V; however, it 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 ADXL321 output is ratiometric, so the sensitivity (or scale factor) varies proportionally to supply voltage. At VS = 5 V, the sensitivity is typically 100 mV/g. At VS = 2.4 V, the sensitivity is typically 45 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. USE AS A DUAL-AXIS TILT SENSOR An accelerometer is most sensitive to tilt when its sensitive axis is perpendicular to the force of gravity (that is, when it is parallel to the earth’s surface). At this orientation, its 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 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 = arcsine(AX/1 g) ROLL = arcsine(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. 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 190 µg/√Hz, while at VS = 2.4 V, the noise density is typically 400 µg/√Hz, 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 ADXL321 is approximately 80 mV. At VS = 2.4 V, the self-test response is approximately 8 mV. The supply current decreases as the supply voltage decreases. Typical current consumption at VS = 5 V is 750 µA, and typical current consumption at VS = 2.4 V is 350 µA. Rev. 0 | Page 13 of 16 ADXL321 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 21. 16-Lead Lead Frame Chip Scale Package [MQ_LFCSP] 4 mm × 4 mm Body, Thick Quad (CP-16-5) Dimensions shown in millimeters (Drawing Not to Scale) ORDERING GUIDE Model ADXL321JCP1 ADXL321JCP–REEL1 ADXL321EB 1 Measurement Range ±18 g ±18 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 16-Lead LFCSP Evaluation Board Package Option CP-16-5 CP-16-5 ADXL321 NOTES Rev. 0 | Page 15 of 16 ADXL321 NOTES © 2004 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D05291–0–12/04(0) Rev. 0 | Page 16 of 16