ADXL202E

REV.A

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Technical content

REV.A 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 which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. a ADXL202E* Tel: 781/329-4700 World Wide Web Site: http://www.analog.com Fax: 781/326-8703 © Analog Devices, Inc., 2000 Low-Cost /H115502 g Dual-Axis Accelerometer with Duty Cycle Output FUNCTIONAL BLOCK DIAGRAM ANALOG TO DUTY CYCLE (ADC) C O U N T E R /H9262P XOUT YOUT DEMOD DEMOD RFILT 32k/H9024 RFILT 32k/H9024 ADXL202E RSET CY YFILT SELF-TESTXFILT CX OSCILLATOR COM Y SENSOR X SENSOR 3V TO 5.25V VDD CDC 0g = 50% DUTY CYCLE T2 = RSET/125M/H9024

FEATURES

2-Axis Acceleration Sensor on a Single IC Chip 5mm /H11547 5mm /H11547 2mm Ultrasmall Chip Scale Package 2mg Resolution at 60Hz Low-Power < 0.6mA Direct Interface to Low-Cost Microcontrollers via Duty Cycle Output BW Adjustment with a Single Capacitor 3V to 5.25V Single Supply Operation 1000g Shock Survival

APPLICATIONS

2-Axis Tilt Sensing with Faster Response than Electrolytic, Mercury, or Thermal Sensors Computer Peripherals Information Appliances Alarms and Motion Detectors Disk Drives Vehicle Security GENERAL DESCRIPTION The ADXL202E is a low-cost, low-power, complete 2-axis acceler- ometer with a digital output, all on a single monolithic IC. It is an improved version of the ADXL202AQC/JQC. The ADXL202E will measure accelerations with a full-scale range of /H110062 g. The ADXL202E can measure both dynamic acceleration (e.g., vibra- tion) and static acceleration (e.g., gravity). The outputs are analog voltage or digital signals whose duty cycles (ratio of pulsewidth to period) are proportional to acceleration. The duty cycle outputs can be directly measured by a micro- processor counter, without an A/D converter or glue logic. The duty cycle period is adjustable from 0.5 ms to 10 ms via a single resistor (R SET). *Patents Pending The typical noise floor is 200 /H9262g√Hz, allowing signals below 2m g (at 60 Hz bandwidth) to be resolved. The bandwidth of the accelerometer is set with capacitors CX and CY at the XFILT and YFILT pins. An analog output can be recon- structed by filtering the duty cycle output. The ADXL202E is available in 5 mm /H11003 5 mm /H11003 2 mm 8-lead hermetic LCC package.

REV. A–2– ADXL202E–SPECIFICATIONS TPC1 ADXL202JE ADXL202AE Parameter Conditions Graph Min Typ Max Min Typ Max Unit SENSOR INPUT Each Axis Measurement Range 2 ± 2 ± 2 g Nonlinearity Best Fit Straight Line 0.2 0.2 % of FS Alignment Error 3 X ± 1 ± 1 Degrees Alignment Error X Sensor to Y Sensor 0.01 0.01 Degrees Cross-Axis Sensitivity 4 X ± 2 ± 2% SENSITIVITY Each Axis Duty Cycle per g T1/T2, VDD = 5 V X 10.5 12.5 14.5 10 12.5 15 %/ g Duty Cycle per g T1/T2, VDD = 3 V X 9.0 11 13.0 8.5 11 13.5 %/ g Sensitivity X FILT, YFILT VDD = 5 V X 265 312 360 250 312 375 mV/ g Sensitivity X FILT, YFILT VDD = 3 V X 140 167 195 140 167 200 mV/ g Temperature Drift 5 Delta from 25 /H11034CX ± 0.5 ± 0.5 % ZERO g BIAS LEVEL Each Axis 0 g Duty Cycle T1/T2, V DD = 5 V X 3 4 5 06 6 3 0 5 07 0 % 0 g Duty Cycle T1/T2, V DD = 3 V X 3 1 5 06 9 3 1 5 06 9 % 0 g Offset vs. Temperature 5 Delta from 25 /H11034C X 2.0 2.0 m g//H11034C NOISE PERFORMANCE Noise Density @ 25 /H11034C X 200 200 1000 µg√Hz rms FREQUENCY RESPONSE 3 dB Bandwidth At Pins X FILT, YFILT 6 6 kHz Sensor Resonant Frequency 10 10 kHz FILTER RFILT Tolerance 32 k Ω Nominal ± 15 ± 15 % Minimum Capacitance At Pins X FILT, YFILT 1000 1000 pF SELF-TEST Duty Cycle Change Self-Test “0” to “1” 10 10 % DUTY CYCLE OUTPUT STAGE FSET RSET = 125 kΩ 0.7 1.3 0.7 1.3 kHz Output High Voltage I = 25 µAV S – 200 mV V S – 200 mV V Output Low Voltage I = 25 µA 200 200 mV T2 Drift vs. Temperature 50 50 ppm/ /H11034C Rise/Fall Time 200 200 ns POWER SUPPLY Operating Voltage Range 3 5.25 3.0 5.25 V Quiescent Supply Current 0.6 1.0 0.6 1.0 mA Turn-On Time C FILT in µF 160 /H11003 CFILT + 0.3 160 /H11003 CFILT + 0.3 ms TEMPERATURE RANGE Specified Performance AE –40 +85 /H11034C Operating Range 0 70 –40 +85 /H11034C NOTES 1Typical Performance Characteristics. 2Guaranteed by measurement of initial offset and sensitivity. 3Alignment error is specified as the angle between the true and indicated axis of sensitivity (see TPC 15). 4Cross-axis sensitivity is the algebraic sum of the alignment and the inherent sensitivity errors. 5Defined as the output change from ambient to maximum temperature or ambient to minimum temperature. Specifications subject to change without notice. (TA = TMIN to TMAX, TA = 25/H11543C for J Grade only, VDD = 5 V, RSET = 125 k/H9024, Acceleration = 0 g, unless otherwise noted.)

REV. A ADXL202E –3– ABSOLUTE MAXIMUM RATINGS * Output Short Circuit Duration, (Any Pin to Common) *Stresses above those listed under Absolute Maximum Ratings may cause perma- nent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions above those indicate in the operational sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. Package Characteristics Package Weight /H9258JA /H9258JC Device 8-Lead LCC 120 °C/W tbd °C/W <1.0 grams ORDERING GUIDE No. Specified Temperature Package Package Model of Axes Voltage Range Description Option ADXL202JE 2 3 V to 5 V 0 to 70 /H11034C 8-Lead LCC E-8 ADXL202AE 2 3 V to 5 V –40 /H11034C to +85/H11034C 8-Lead LCC E-8 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 the ADXL202E 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. WARNING! ESD SENSITIVE DEVICE PIN FUNCTION DESCRIPTIONS Pin No. Mnemonic Description

1 ST Self-Test

2 T2 Connect R SET to Set T2 Period

3 COM Common

OUT Y-Channel Duty Cycle Output 5X OUT X-Channel Duty Cycle Output 6Y FILT Y-Channel Filter Pin 7X FILT X-Channel Filter Pin 8V DD 3 V to 5.25 V Drops onto hard surfaces can cause shocks of greater than 1000g and exceed the absolute maximum rating of the device. Care should be exercised in handling to avoid damage. PIN CONFIGURATION ST COMXOUT YFILT XFILT VDD YOUT BOTTOM VIEW

REV. A ADXL202E –4– –Typical Performance Characteristics* VOLTS 1.28 PERCENT OF PARTS TPC 1. X-Axis Zero g Bias Distribution at XFILT, VDD = 3V VOLTS 1.25 PERCENT OF PARTS TPC 2. Y-Axis Zero g Bias Distribution at YFILT, VDD = 3V V/g 0.142 PERCENT OF PARTS TPC 3. X-Axis Sensitivity Distribution at XFILT, VDD = 3V VDD = 3 V V DD = 5 V *Data taken from 4500 parts over 3 lots minimum. VOLTS 2.05 PERCENT OF PARTS TPC 4. X-Axis Zero g Bias Distribution at XFILT, VDD = 5V VOLTS 2.05 PERCENT OF PARTS TPC 5. Y-Axis Zero g Bias Distribution at YFILT, VDD = 5V V/g 0.26 PERCENT OF PARTS TPC 6. X-Axis Sensitivity Distribution at XFILT, VDD = 5V

REV. A ADXL202E –5– V/g 0.142 PERCENT OF PARTS TPC 7. Y-Axis Sensitivity Distribution at YFILT, VDD = 3V PERCENT DUTY CYCLE/g 9.50 PERCENT OF PARTS 9.90 10.4 10.8 11.8 11.3 12.2 12.7 TPC 8. X-Axis Sensitivity at XOUT, VDD = 3V PERCENT DUTY CYCLE/g 9.50 PERCENT OF PARTS 9.90 10.4 10.8 11.8 11.3 12.2 12.7 TPC 9. Y-Axis Sensitivity at YOUT, VDD = 3V VDD = 3 V V DD = 5 V V/g 0.26 PERCENT OF PARTS TPC 10. Y-Axis Sensitivity Distribution at YFILT, VDD = 5V PERCENT DUTY CYCLE/g 10.3 PERCENT OF PARTS 10.8 11.3 11.8 12.8 12.3 13.3 13.8 TPC 11. X-Axis Sensitivity at XOUT, VDD = 5V PERCENT DUTY CYCLE/g 10.6 PERCENT OF PARTS 11.0 11.6 12.0 13.0 12.6 13.6 14.0 TPC 12. Y-Axis Sensitivity at YOUT, VDD = 5V

REV. A ADXL202E –6– NOISE DENSITY – /H9262g Hz rms 230 FREQUENCY – % 250 270 290 310 330 350 390 410 370 TPC 13. Noise Density Distribution, VDD = 3V TEMPERATURE – /H11543C 0.7 0–40 100 –20 SUPPLY CURRENT – mA 0 2 04 0 6 08 0 0.6 0.4 0.3 0.2 0.1 0.5 VS = 5 VDC VS = 3.5 VDC TPC 14. Typical Supply Current vs. Temperature DEGREES OF MISALIGNMENT –1.375 0.375 % OF PARTS –1.125 –0.875 –0.625 –0.375 –0.125 0.625 0.875 1.125 1.375 0.125 TPC 15. Rotational Die Alignment NOISE DENSITY – /H9262g Hz rms 150 FREQUENCY – % 170 190 210 230 250 270 290 310 TPC 16. Noise Density Distribution, VDD = 5V PERCENT – % PERCENT OF PARTS – % 0123 –2 –1 TPC 17. Cross-Axis Sensitivity Distribution 0 0.4 0.8 1.2 1.4 TIME – ms VOLTS CFILT = 0.01/H9262F VDD XOUT TPC 18. Typical Turn-On Time

REV. A ADXL202E –7– mg/ /H11543C –2.08 PERCENT OF PARTS – % TPC 19. X-Axis Zero g Drift Due to Temperature Distribution, –40°C to +85°C PERCENT//H11543C –0.046 PERCENT OF PARTS – %30 –0.013 0.004 TPC 20. X-Axis Sensitivity Drift at X FILT Due to Temperature Dis tribution, –40°C to +85°C TEMPERATURE – /H11543C 400 –50 mg –25 0 25 50 75 100 300 200 100 –100 –200 –300 TPC 21. Typical X-Axis Zero g vs. Output for 16 Parts mg/ /H11543C –0.73 PERCENT OF PARTS – % TPC 22. Y-Axis Zero g Drift Due to Temperature Distribution, –40°C to +85°C PERCENT//H11543C –0.046 PERCENT OF PARTS – % –0.013 0.004 TPC 23. Y-Axis Sensitivity Drift at Y FILT Due to Temperature Dis tribution, –40°C to +85°C TEMPERATURE – /H11543C 400 –50 mg –25 0 25 50 75 100 300 200 100 –200 –300 –400 –100 TPC 24. Typical Y-Axis Zero g vs. Output for 16 Parts

C(X, Y) is required in all cases. cycle periods between 0.5 ms and 10 ms. applications where accelerations of greater than ±2 g are expected. output involves selecting a duty cycle period and a filter capacitor. be 10% at the duty cycle outputs (corresponding to 800 m g). The ADXL202E ’s digital output is a duty cycle modulator. device including zero g offset error and sensitivity error. T2 does not have to be measured for every measurement cycle. Figure 3. Block Diagram

REV. A ADXL202E –10– With the single pole roll-off characteristic, the typical noise of the ADXL202E is determined by the following equation: Noise rms g Hz BW() = () ××()200 1 6µ /. At 100 Hz the noise will be: Noise rms g Hz mg() = () ×× ()  =200 100 1 6 2 53µ /. . Often the peak value of the noise is desired. Peak-to-peak noise can only be estimated by statistical methods. Table III is useful for estimating the probabilities of exceeding various peak values, given the rms value. Table III. Estimation of Peak-to-Peak Noise % of Time that Noise Nominal Peak-to-Peak Will Exceed Nominal Value Peak-to-Peak Value 2.0 × rms 32% 4.0 × rms 4.6% 6.0 × rms 0.27% 8.0 × rms 0.006% The peak-to-peak noise value will give the best estimate of the uncertainty in a single measurement. Table IV gives typical noise output of the ADXL202E for various CX and CY values. Table IV. Filter Capacitor Selection, C X and CY Peak-to-Peak Noise Estimate 95% Bandwidth C X, CY rms Noise Probability (rms /H11547 4) 10 Hz 0.47 µF 0.8 m g 3.2 mg 50 Hz 0.10 µF 1.8 m g 7.2 mg 100 Hz 0.05 µF 2.5 m g 10.1 mg 200 Hz 0.027 µF 3.6 m g 14.3 mg 500 Hz 0.01 µF 5.7 m g 22.6 mg CHOOSING T2 AND COUNTER FREQUENCY: DESIGN TRADE-OFFS The noise level is one determinant of accelerometer resolution. The second relates to the measurement resolution of the counter when decoding the duty cycle output. The ADXL202E ’s duty cycle converter has a resolution of approximately 14 bits; better resolution than the accelerometer itself. The actual resolution of the acceleration signal is, how- ever, limited by the time resolution of the counting devices used to decode the duty cycle. The faster the counter clock, the higher the resolution of the duty cycle and the shorter the T2 period can be for a given resolution. The following table shows some of the trade-offs. It is important to note that this is the resolution due to the microprocessors ’ counter. It is probable that the accelerometer’s noise floor may set the lower limit on the resolu- tion, as discussed in the previous section. MICROCOMPUTER INTERFACES The ADXL202E is specifically designed to work with low-cost microcontrollers. Specific code sets, reference designs, and applica- tion notes are available from the factory. This section will outline a general design procedure and discuss the various trade-offs that need to be considered. The designer should have some idea of the required performance of the system in terms of: Resolution: the smallest signal change that needs to be detected. Bandwidth: the highest frequency that needs to be detected. Acquisition Time: the time that will be available to acquire the signal on each axis. These requirements will help to determine the accelerometer band- width, the speed of the microcontroller clock and the length of the T2 period. When selecting a microcontroller it is helpful to have a counter timer port available. The microcontroller should have provisions for software calibration. While the ADXL202E is a highly accurate accelerometer, it has a wide tolerance for initial offset. The easi- est way to null this offset is with a calibration factor saved on the microcontroller or by a user calibration for zero g. In the case where the offset is calibrated during manufacture, there are several options, including external EEPROM and microcontrollers with “one-time programmable ” features. DESIGN TRADE-OFFS FOR SELECTING FILTER CHARACTERISTICS: THE NOISE/BW TRADE-OFF The accelerometer bandwidth selected will determine the measure- ment resolution (smallest detectable acceleration). Filtering can be used to lower the noise floor and improve the resolution of the accelerometer. Resolution is dependent on both the analog filter bandwidth at X FILT and YFILT and on the speed of the micro- controller counter. The analog output of the ADXL202E has a typical bandwidth of 5 kHz, while the duty cycle modulators’ bandwidth is 500 Hz. The user must filter the signal at this point to limit aliasing errors. To minimize DCM errors the analog bandwidth should be less than 1/10 the DCM frequency. Analog bandwidth may be increased to up to 1/2 the DCM frequency in many applications. This will result in greater dynamic error generated at the DCM. The analog bandwidth may be further decreased to reduce noise and improve resolution. The ADXL202E noise has the character- istics of white Gaussian noise that contributes equally at all frequencies and is described in terms of µg per root Hz; i.e., the noise is proportional to the square root of the bandw idth of the accelerometer. It is recommended that the user limit bandwidth to the lowest frequency needed by the application, to maximize the resolution and dynamic range of the accelerometer.

REV. A–12– PRINTED IN U.S.A. ADXL202E OUTLINE DIMENSIONS Dimensions shown in inches and (mm). 8-Terminal Ceramic Leadless Chip Carrier (E-8) BOTTOM VIEW 0.025 (0.64) 0.075 (1.91) 0.099 (2.50) 0.099 (2.50) /H11632 0.015 (0.38)R0.008 (0.20) SQ 0.177 (4.50) SQ TOP VIEW (0.20) 0.070 (1.78) CONTROLLING DIMENSIONS ARE IN MILLIMETERS 0.050 (1.27) 0.050 (1.27) USING THE ADXL202E IN VERY LOW POWER An application note outlining low power strategies for the ADXL202E is available. Some key points are presented here. It is possible to reduce the ADXL202E ’s average current from 0.6 mA to less than 20 µA by using the following techniques: 1. Power Cycle the accelerometer. 2. Run the accelerometer at a Lower Voltage, (Down to 3 V). Power Cycling with an External A/D Depending on the value of the X FILT capacitor, the ADXL202E is capable of turning on and giving a good reading in 1.6 ms. Most microcontroller based A/Ds can acquire a reading in another 25µs. Thus it is possible to turn on the ADXL202E and take a reading in <2 ms. If we assume that a 20 Hz sam ple rate is sufficient, the total current required to take 20 samples is 2 ms × 20 samples/s × 0.6 mA = 24 µA average current. Running the part at 3 V will reduce the supply current from 0.6 mA to 0.4 mA, bringing the average current down to 16 µA. The A/D should read the analog output of the ADXL202E at the XFILT and YFILT pins. A buffer amplifier is recommended, and may be required in any case to amplify the analog output to give enough resolution with an 8-bit to 10-bit converter. Power Cycling When Using the Digital Output An alternative is to run the microcontroller at a higher clock rate and put it into shutdown between readings, allowing the use of the digital output. In this approach the ADXL202E should be set at its fastest sample rate (T2 = 0.5 ms), with a 500 Hz filter at X FILT and YFILT. The concept is to acquire a reading as quickly as pos- sible and then shut down the ADXL202E and the microcontroller until the next sample is needed. In either of the above approaches, the ADXL202E can be turned on and off directly using a digital port pin on the microcontroller to power the accelerometer without additional components. CALIBRATING THE ADXL202E/ADXL210 The initial value of the offset and scale factor for the ADXL202E will require calibration for applications such as tilt measurement. The ADXL202E architecture has been designed so that these calibrations take place in the software of the microcontroller used to decode the duty cycle signal. Calibration factors can be stored in EEPROM or determined at turn-on and saved in dynamic memory. For low g applications, the force of gravity is the most stable, accurate and convenient acceleration reference available. A reading of the 0 g point can be determined by orientating the d evice par- allel to the earth’s surface and then reading the output. A more accurate calibration method is to make measurements at +1 g and –1 g. The sensitivity can be determined by the two measurements. To calibrate, the accelerometer ’s measurement axis is pointed directly at the earth. The 1 g reading is saved and the sensor is turned 180° to measure –1 g. Using the two readings, the sensi- tivity is: Let A = Accelerometer output with axis oriented to +1 g Let B = Accelerometer output with axis oriented to –1 g then: Sensitivity = [A – B]/2 g For example, if the +1 g reading (A) is 55% duty cycle and the –1 g reading (B) is 32% duty cycle, then: Sensitivity = [55% – 32%]/2 g = 11.5%/g These equations apply whether the output is analog or duty cycle. Application notes outlining algorithms for calculating accelera- tion from duty cycle and automated calibration routines are available from the factory.