Small, Low Power, 3-Axis ±200 g Accelerometer ADXL377 Data Sheet FEATURES GENERAL DESCRIPTION 3-axis sensing Small, low profile package 3 mm × 3 mm × 1.45 mm LFCSP Low power: 300 µA (typical) Single-supply operation: 1.8 V to 3.6 V 10,000 g shock survival Excellent temperature stability Bandwidth adjustment with a single capacitor per axis RoHS/WEEE and lead-free compliant The ADXL377 is a small, thin, low power, complete 3-axis accelerometer with signal conditioned voltage outputs. The ADXL377 measures acceleration resulting from motion, shock, or vibration with a typical full-scale range of ±200 g. APPLICATIONS The ADXL377 is available in a small, low profile, 3 mm × 3 mm × 1.45 mm, 16-lead lead frame chip scale package (LFCSP_LQ). The user selects the bandwidth of the accelerometer using the CX, CY, and CZ capacitors at the XOUT, YOUT, and ZOUT pins. Bandwidths can be selected to suit the application, with a range of 0.5 Hz to 1300 Hz for the x-axis and y-axis and a range of 0.5 Hz to 1000 Hz for the z-axis. Concussion and head trauma detection High force event detection FUNCTIONAL BLOCK DIAGRAM +3V VS ADXL377 OUTPUT AMPLIFIERS AC AMPLIFIER CDC 32kΩ XOUT CX DEMODULATOR 32kΩ YOUT CY 3-AXIS SENSOR 32kΩ ZOUT CZ ST 10765-001 GND Figure 1. Rev. 0 Document Feedback 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 ©2012 Analog Devices, Inc. All rights reserved. Technical Support www.analog.com ADXL377 Data Sheet TABLE OF CONTENTS Features .............................................................................................. 1 Performance ...................................................................................8 Applications ....................................................................................... 1 Applications Information .................................................................9 General Description ......................................................................... 1 Power Supply Decoupling ............................................................9 Functional Block Diagram .............................................................. 1 Setting the Bandwidth Using CX, CY, and CZ .............................9 Revision History ............................................................................... 2 Self-Test ..........................................................................................9 Specifications..................................................................................... 3 Selecting Filter Characteristics: Noise/Bandwidth Trade-Off....9 Absolute Maximum Ratings ............................................................ 4 Axes of Acceleration Sensitivity ............................................... 10 ESD Caution .................................................................................. 4 Layout and Design Recommendations ................................... 11 Pin Configuration and Function Descriptions ............................. 5 Outline Dimensions ....................................................................... 12 Typical Performance Characteristics ............................................. 6 Ordering Guide .......................................................................... 12 Theory of Operation ........................................................................ 8 Mechanical Sensor........................................................................ 8 REVISION HISTORY 9/12—Revision 0: Initial Version Rev. 0 | Page 2 of 12 Data Sheet ADXL377 SPECIFICATIONS TA = 25°C, VS = 3 V, CX = CY = CZ = 0.1 μF, acceleration = 0 g, unless otherwise noted. All minimum and maximum specifications are guaranteed. Typical specifications are not guaranteed. Table 1. Parameter SENSOR INPUT Measurement Range Nonlinearity Cross-Axis Sensitivity1 SENSITIVITY, RATIOMETRIC2 Sensitivity at XOUT, YOUT, and ZOUT Sensitivity Change Due to Temperature3 ZERO g BIAS LEVEL, RATIOMETRIC Zero g Voltage Zero g Offset vs. Temperature X-Axis and Y-Axis Z-Axis NOISE PERFORMANCE Noise Density XOUT and YOUT ZOUT FREQUENCY RESPONSE4 Bandwidth5 XOUT and YOUT ZOUT RFILT Tolerance Sensor Resonant Frequency SELF-TEST6 Logic Input Low Logic Input High ST Actuation Current Output Change At XOUT At YOUT At ZOUT OUTPUT AMPLIFIER Output Swing Low Output Swing High POWER SUPPLY Operating Voltage Range7 Supply Current Turn-On Time8 OPERATING TEMPERATURE RANGE Test Conditions/Comments Each axis Min Typ Max g % % ±200 ±0.5 ±1.4 % of full scale up to 180 g Unit Each axis VS = 3 V VS = 3 V 5.8 6.5 ±0.02 7.2 mV/g %/°C VS = 3 V, TA = 25°C 1.4 1.5 1.6 V ±12 ±30 mg/°C mg/°C 2.7 4.3 mg/√Hz mg/√Hz 1300 1000 32 ± 15% 16.5 Hz Hz kΩ kHz 0.6 2.4 60 V V μA −6.5 6.5 11.5 mV mV mV 0.1 2.8 V V No external filter Self-test, 0 to 1 No load 1.8 VS = 3 V No external filter −40 1 3.0 300 1 3.6 +85 V μA ms °C Defined as coupling between any two axes. Sensitivity is essentially ratiometric to VS. 3 Defined as the output change from ambient temperature to maximum temperature or from ambient temperature to minimum temperature. 4 Actual frequency response controlled by user-supplied external filter capacitors (CX, CY, and CZ). 5 Bandwidth with external capacitors = 1/(2π × 32 kΩ × Cx). 6 Self-test response changes cubically with VS. 7 Tested at 3.0 V and guaranteed by design only (not tested) to work over the full voltage range from 1.8 V to 3.6 V. 8 Turn-on time is dependent on CX, CY, and CZ and is approximately 160 × (CX or CY or CZ) + 1, where CX, CY, and CZ are in μF and the resulting turn-on time is in ms. 2 Rev. 0 | Page 3 of 12 ADXL377 Data Sheet ABSOLUTE MAXIMUM RATINGS ESD CAUTION Table 2. Parameter Acceleration (Any Axis) Unpowered Powered VS All Other Pins Output Short-Circuit Duration (Any Pin to Ground) Operating Temperature Range Storage Temperature Range Rating 10,000 g 10,000 g −0.3 V to +3.6 V (GND − 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. Rev. 0 | Page 4 of 12 Data Sheet ADXL377 RES ST ZOUT VS VS NC PIN CONFIGURATION AND FUNCTION DESCRIPTIONS 16 15 14 13 1 ADXL377 2 TOP VIEW (Not to Scale) 12 NC 11 NC 10 NC 9 NC +Z 5 6 7 8 NC +X GND YOUT 4 GND 3 XOUT RES NOTES 1. NC = NO CONNECT. 2. THE EXPOSED PAD IS NOT INTERNALLY CONNECTED, BUT SHOULD BE SOLDERED FOR MECHANICAL INTEGRITY. 10765-002 +Y Figure 2. Pin Configuration Table 3. Pin Function Descriptions Pin No. 1, 3 2 4 5 6, 7 8 to 13 14, 15 16 Mnemonic RES ST YOUT XOUT GND NC VS ZOUT EPAD Description Reserved. This pin must be connected to GND or left open. Self-Test. Y Channel Output. X Channel Output. Must be connected to ground. No Connect. Not internally connected. Supply Voltage. 3.0 V typical. Z Channel Output. Exposed Pad. The exposed pad is not internally connected, but should be soldered for mechanical integrity. Rev. 0 | Page 5 of 12 ADXL377 Data Sheet TYPICAL PERFORMANCE CHARACTERISTICS N > 250 for all typical performance figures, unless otherwise noted. N is the number of parts tested and used to produce the histograms. 1.525 35 1.520 1.515 25 OUTPUT VOLTAGE (V) 20 15 10 1.510 1.505 1.500 1.495 1.490 5 OUTPUT VOLTAGE (V) 1.480 –60 10765-003 1.5200 1.5175 1.5150 1.5125 1.5100 1.5075 1.5050 1.5025 1.5000 1.4975 1.4950 1.4925 1.4900 1.4875 1.4850 1.4825 1.4800 0 1.485 –40 –20 0 20 40 60 80 100 TEMPERATURE (°C) Figure 3. X-Axis Zero g Output Voltage at 25°C, VS = 3 V 10765-006 PERCENT OF POPULATION (%) 30 Figure 6. X-Axis Zero g Offset vs. Temperature, VS = 3 V (14 Parts Soldered to PCB) 1.525 30 1.515 OUTPUT VOLTAGE (V) PERCENT OF POPULATION (%) 1.520 25 20 15 10 1.510 1.505 1.500 1.495 1.490 5 OUTPUT VOLTAGE (V) 80 1.520 70 1.515 60 50 40 30 1.480 –60 10765-005 1.5200 1.5175 1.5150 1.5125 1.5100 1.5075 1.5050 1.5025 1.5000 1.4975 1.4950 1.4925 100 1.495 1.485 1.4900 80 1.500 10 1.4875 60 1.505 1.490 1.4850 40 1.510 20 1.4825 20 –40 –20 0 20 40 60 80 TEMPERATURE (°C) Figure 8. Z-Axis Zero g Offset vs. Temperature, VS = 3 V (14 Parts Soldered to PCB) Figure 5. Z-Axis One g Output Voltage at 25°C, VS = 3 V Rev. 0 | Page 6 of 12 100 10765-008 OUTPUT VOLTAGE (V) 1.525 1.4800 PERCENT OF POPULATION (%) 0 Figure 7. Y-Axis Zero g Offset vs. Temperature, VS = 3 V (14 Parts Soldered to PCB) 90 OUTPUT VOLTAGE (V) –20 TEMPERATURE (°C) Figure 4. Y-Axis Zero g Output Voltage at 25°C, VS = 3 V 0 –40 10765-007 1.480 –60 10765-004 1.5200 1.5175 1.5150 1.5125 1.5100 1.5075 1.5050 1.5025 1.5000 1.4975 1.4950 1.4925 1.4900 1.4875 1.4850 1.4825 0 1.4800 1.485 ADXL377 25 250 20 200 15 150 OUTPUT (g) PERCENT OF POPULATION (%) Data Sheet 10 100 50 5 0 150 200 Figure 12. Typical Output Linearity over the Dynamic Range 10 30 SENSITIVITY (mV/g) 25 20 15 10 SENSITIVITY (mV/g) 14 12 10 8 6 4 10765-011 7.00 6.95 6.90 6.85 6.80 6.75 6.70 6.65 6.60 6.55 6.50 6.45 6.40 6.35 6.30 6.25 6.20 6.15 6.10 6.05 2 6.00 1k Figure 13. Typical Frequency Response 16 SENSITIVITY (mV/g) 100 FREQUENCY (Hz) Figure 10. Y-Axis Sensitivity at 25°C, VS = 3 V 0 X-AXIS, Y-AXIS RESPONSE Z-AXIS RESPONSE Figure 11. Z-Axis Sensitivity at 25°C, VS = 3 V Rev. 0 | Page 7 of 12 10k 10765-013 1 10 10765-010 7.00 6.95 6.90 6.85 6.80 6.75 6.70 6.65 6.60 6.55 6.50 6.45 6.40 6.35 6.30 6.25 6.20 6.15 6.10 0 6.05 5 6.00 PERCENT OF POPULATION (%) 100 REFERENCE ACCELERATION (g) Figure 9. X-Axis Sensitivity at 25°C, VS = 3 V PERCENT OF POPULATION (%) 50 10765-012 7.00 SENSITIVITY (mV/g) 0 10765-009 6.95 6.90 6.85 6.80 6.75 6.70 6.65 6.60 6.55 6.50 6.45 6.40 6.35 6.30 6.25 6.20 6.15 6.10 6.05 0 6.00 X-AXIS Y-AXIS Z-AXIS ADXL377 Data Sheet THEORY OF OPERATION The ADXL377 is a complete 3-axis acceleration measurement system with a typical measurement range of ±200 g. The ADXL377 contains a polysilicon, surface-micromachined sensor and signal conditioning circuitry to implement an open-loop acceleration measurement architecture. The output signals are analog voltages that are proportional to acceleration. The accelerometer can measure the static acceleration of gravity in tilt-sensing applications, as well as dynamic acceleration resulting from motion, shock, or vibration. 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 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 moving mass and unbalances the differential capacitor, resulting in a sensor output whose amplitude is proportional to acceleration. Phase-sensitive demodulation techniques are then used to determine the magnitude and direction of the acceleration. The demodulator 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. MECHANICAL SENSOR The ADXL377 uses a single structure for sensing the acceleration in the x-axis, y-axis, and z-axis. As a result, the three sense directions are highly orthogonal with little cross-axis sensitivity. Mechanical misalignment of the sensor die to the package or misalignment of the package to the PCB is the chief source of cross-axis sensitivity. Mechanical misalignment can be calibrated at the system level. PERFORMANCE Rather than using additional temperature compensation circuitry, the ADXL377 uses innovative design techniques to ensure high performance. As a result, there is neither quantization error nor nonmonotonic behavior, and temperature hysteresis is very low. Rev. 0 | Page 8 of 12 Data Sheet ADXL377 APPLICATIONS INFORMATION POWER SUPPLY DECOUPLING For most applications, a single 0.1 µF capacitor, CDC, placed close to the ADXL377 supply pins adequately decouples the accelerometer from noise on the power supply. However, in applications where noise is present at the 50 kHz internal clock frequency (or any harmonic thereof), additional care in power supply bypassing is required because this noise can cause errors in acceleration measurement. If additional decoupling is needed, a 100 Ω (or smaller) resistor or ferrite bead can be inserted in the supply line. In addition, a larger bulk bypass capacitor (1 µF or greater) can be added in parallel to CDC. Ensure that the connection from the ADXL377 ground to the power supply ground is low impedance because noise transmitted through ground has a similar effect as noise transmitted through VS. SETTING THE BANDWIDTH USING CX, CY, AND CZ The ADXL377 has provisions for band-limiting the XOUT, YOUT, and ZOUT pins. A capacitor must be added at each of 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 × Cx) or more simply, f−3 dB = 5 µF/Cx The tolerance of the internal resistor (RFILT) typically varies by as much as ±15% of its nominal value (32 kΩ), and the bandwidth varies accordingly. A minimum capacitance of 1000 pF for CX, CY, and CZ is recommended in all cases. Table 4. Filter Capacitor Selection for CX, CY, and CZ Bandwidth (Hz) 50 100 200 500 1000 Capacitor (µF) 0.10 0.05 0.025 0.01 0.005 Never expose the ST pin to voltages greater than VS + 0.3 V. If the system design is such that this condition cannot be guaranteed (for example, if multiple supply voltages are present), it is recommended that a clamping diode with low forward voltage be connected between ST and VS. SELECTING FILTER CHARACTERISTICS: NOISE/BANDWIDTH TRADE-OFF The selected accelerometer bandwidth ultimately determines the measurement resolution (smallest detectable acceleration). Filtering can be used to lower the noise floor, thereby improving the resolution of the accelerometer. Resolution is dependent on the analog filter bandwidth at XOUT, YOUT, and ZOUT. The output of the ADXL377 has a typical bandwidth of 1000 Hz. The user must filter the signal at this point to limit aliasing errors. The analog bandwidth must be no more than half the analog-todigital sampling frequency to minimize aliasing. The analog bandwidth can be decreased further to reduce noise and improve resolution. The ADXL377 noise has the characteristics of white Gaussian noise, which contributes equally at all frequencies and is described in terms of µg/√Hz (that is, the noise is proportional to the square root of the accelerometer bandwidth). Limit the bandwidth to the lowest frequency required by the application to maximize the resolution and dynamic range of the accelerometer. With the single-pole roll-off characteristic, the typical noise of the ADXL377 is determined by rms Noise = Noise Density × ( BW × 1.6 ) It is often useful to know the peak value of the noise. Peak-topeak noise can only be estimated by statistical methods. Table 5 can be used to estimate the probability of exceeding various peak values, given the rms value. Table 5. 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 whether the accelerometer is functional. The typical change in output is −1.08 g (corresponding to −6.5 mV) for the x-axis, +1.08 g (or +6.5 mV) for the y-axis, and +1.83 g (or +11.5 mV) for the z-axis. The ST pin can be left open circuit or connected to ground (GND) in normal use. Peak-to-Peak Value 2 × rms 4 × rms 6 × rms 8 × rms Rev. 0 | Page 9 of 12 Percentage of Time That Noise Exceeds Nominal Peak-to-Peak Value (%) 32 4.6 0.27 0.006 ADXL377 Data Sheet AXES OF ACCELERATION SENSITIVITY Figure 14 shows the axes of sensitivity for the accelerometer. Figure 15 shows the output response when the accelerometer is oriented parallel to each of these axes. AZ AX 10765-014 AY Figure 14. Axes of Acceleration Sensitivity (Corresponding Output Voltage Increases When Accelerated Along the Sensitive Axis) XOUT = –1g YOUT = 0g ZOUT = 0g TOP GRAVITY TOP TOP XOUT = 0g YOUT = –1g ZOUT = 0g TOP XOUT = 1g YOUT = 0g ZOUT = 0g XOUT = 0g YOUT = 0g ZOUT = 1g Figure 15. Output Response vs. Orientation to Gravity Rev. 0 | Page 10 of 12 XOUT = 0g YOUT = 0g ZOUT = –1g 10765-015 XOUT = 0g YOUT = 1g ZOUT = 0g Data Sheet ADXL377 LAYOUT AND DESIGN RECOMMENDATIONS Figure 16 shows the recommended soldering profile; Table 6 describes the profile features. Figure 17 shows the recommended PCB layout or solder land drawing. CRITICAL ZONE TL TO TP tP TP TL tL TSMAX TSMIN tS RAMP-DOWN PREHEAT 10765-016 TEMPERATURE RAMP-UP t25°C TIME Figure 16. Recommended Soldering Profile Table 6. Recommended Soldering Profile Profile Feature Average Ramp Rate (TL to TP) Preheat Minimum Temperature (TSMIN) Maximum Temperature (TSMAX) Time, TSMIN to TSMAX (tS) Ramp-Up Rate (TSMAX to TL) Time Maintained Above Liquidous (tL) Liquidous Temperature (TL) Peak Temperature (TP) Time Within 5°C of Actual Peak Temperature (tP) Ramp-Down Rate (TP to TL) Time 25°C to Peak Temperature (t25°C) 0.40 MAX Sn63/Pb37 3°C/sec max Pb-Free 3°C/sec max 100°C 150°C 60 sec to 120 sec 3°C/sec max 60 sec to 150 sec 183°C 240°C + 0°C/−5°C 10 sec to 30 sec 6°C/sec max 6 minutes max 150°C 200°C 60 sec to 180 sec 3°C/sec max 60 sec to 150 sec 217°C 260°C + 0°C/−5°C 20 sec to 40 sec 6°C/sec max 8 minutes max 3 0.25 0.50 0.30 MAX 0.50 3 1.60 0.25 1.60 DIMENSIONS SHOWN IN MILLIMETERS Figure 17. Recommended PCB Layout Rev. 0 | Page 11 of 12 10765-017 CENTER PAD IS NOT INTERNALLY CONNECTED BUT SHOULD BE SOLDERED FOR MECHANICAL INTEGRITY ADXL377 Data Sheet OUTLINE DIMENSIONS PIN 1 INDICATOR 3.10 3.00 SQ 2.90 0.30 0.25 0.18 0.50 BSC 13 PIN 1 INDICATOR 16 1 12 EXPOSED PAD 1.70 1.60 SQ 1.50 9 1.50 1.45 1.40 4 8 0.20 MIN BOTTOM VIEW 0.05 MAX 0.02 NOM COPLANARITY 0.08 0.152 REF SEATING PLANE 5 FOR PROPER CONNECTION OF THE EXPOSED PAD, REFER TO THE PIN CONFIGURATION AND FUNCTION DESCRIPTIONS SECTION OF THIS DATA SHEET. 04-27-2010-A TOP VIEW 0.45 0.40 0.35 Figure 18. 16-Lead Lead Frame Chip Scale Package [LFCSP_LQ] 3 mm × 3 mm Body, Thick Quad (CP-16-28) Dimensions shown in millimeters ORDERING GUIDE Model 1 ADXL377BCPZ-RL ADXL377BCPZ-RL7 EVAL-ADXL377Z 1 Measurement Range ±200 g ±200 g Specified Voltage 3V 3V Temperature Range −40°C to +85°C −40°C to +85°C Z = RoHS Compliant Part. ©2012 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D10765-0-9/12(0) Rev. 0 | Page 12 of 12 Package Description 16-Lead LFCSP_LQ 16-Lead LFCSP_LQ Evaluation Board Package Option CP-16-28 CP-16-28 Branding Y4P Y4P