Small and Thin ±5
g
iMEMS® Accelerometer
ADXL320
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 © 2007 Analog Devices, Inc. All rights reserved.
FEATURES
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 5.25 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
APPLICATIONS
Cost-sensitive motion- and tilt-sensing applications
Smart hand-held devices
Mobile phones
Sports and health-related devices
PC security and PC peripherals
GENERAL DESCRIPTION
The ADXL320 is a low cost, low power, complete dual-axis
accelerometer with signal conditioned voltage outputs, which is
all on a single monolithic IC. The product measures
acceleration with a full-scale range of ±5 g (typical). It can also
measure both dynamic acceleration (vibration) and static
acceleration (gravity).
The ADXL320’s typical noise floor is 250 μg/√Hz, allowing
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 may be selected to suit the application.
The ADXL320 is available in a very thin 4 mm × 4 mm ×
1.45 mm, 16-lead, plastic LFCSP.
FUNCTIONAL BLOCK DIAGRAM
04993-001
ADXL320
SENSOR
+3V
OUTPUT
AMP OUTPUT
AMP
COM ST
V
S
C
DC
DEMOD
AC
AMP
R
FILT
32kΩ
X
OUT
C
X
Y
OUT
C
Y
R
FILT
32kΩ
Figure 1.
ADXL320
Rev. 0 | Page 2 of 16
TABLE OF CONTENTS
Specifications..................................................................................... 3
Absolute Maximum Ratings............................................................ 4
ESD Caution.................................................................................. 4
Pin Configuration and Function Descriptions............................. 5
Typical Performance Characteristics (VS = 3.0 V)....................... 7
Theory of Operation ......................................................................11
Performance................................................................................ 11
Applications..................................................................................... 12
Power Supply Decoupling .........................................................12
Setting the Bandwidth Using CX and CY................................. 12
Self-Test ....................................................................................... 12
Design Trade-Offs for Selecting Filter Characteristics: The
Noise/BW Trade-Off.................................................................. 12
Use with Operating Voltages Other than 3 V............................. 13
Use as a Dual-Axis Tilt Sensor ................................................. 13
Outline Dimensions....................................................................... 14
Ordering Guide .......................................................................... 14
REVISION HISTORY
9/04—Revision 0: Initial Version
ADXL320
Rev. 0 | Page 3 of 16
SPECIFICATIONS1
TA = 25°C, VS = 3 V, CX = CY = 0.1 μF, Acceleration = 0 g, unless otherwise noted.
Table 1.
Parameter Conditions Min Typ Max Unit
SENSOR INPUT Each axis
Measurement Range ±5 g
Nonlinearity % of full scale ±0.2 %
Package Alignment Error ±1 Degrees
Alignment Error X sensor to Y sensor ±0.1 Degrees
Cross Axis Sensitivity ±2 %
SENSITIVITY (RATIOMETRIC)2Each axis
Sensitivity at XOUT, YOUT VS = 3 V 156 174 192 mV/g
Sensitivity Change due to Temperature3VS = 3 V 0.01 %/°C
ZERO g BIAS LEVEL (RATIOMETRIC) Each axis
0 g Voltage at XOUT, YOUT VS = 3 V 1.3 1.5 1.7 V
0 g Offset Versus Temperature ±0.6 mg/°C
NOISE PERFORMANCE
Noise Density @ 25°C 250 μg/√Hz rms
FREQUENCY RESPONSE4
CX, CY Range5 0.002 10 μF
RFILT Tolerance 32 ± 15% kΩ
Sensor Resonant Frequency 5.5 kHz
SELF-TESTT
6
Logic Input Low 0.6 V
Logic Input High 2.4 V
ST Input Resistance to Ground 50 kΩ
Output Change at XOUT, YOUT Self-test 0 to 1 55 mV
OUTPUT AMPLIFIER
Output Swing Low No load 0.3 V
Output Swing High No load 2.5 V
POWER SUPPLY
Operating Voltage Range 2.4 5.25 V
Quiescent Supply Current 0.48 mA
Turn-On Time7 20 ms
TEMPERATURE
Operating Temperature Range −20 70 °C
1 All minimum and maximum specifications are guaranteed. Typical specifications are not guaranteed.
2 Sensitivity is essentially ratiometric to VS. For VS = 2.7 V to 3.3 V, sensitivity is 154 mV/V/g to 194 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.
ADXL320
Rev. 0 | Page 4 of 16
ABSOLUTE MAXIMUM RATINGS
Table 2.
Parameter Rating
Acceleration (Any Axis, Unpowered) 10,000 g
Acceleration (Any Axis, Powered) 10,000 g
VS−0.3 V to +7.0 V
All Other Pins (COM − 0.3 V) to
(VS + 0.3 V)
Output Short-Circuit Duration
(Any Pin to Common) Indefinite
Operating Temperature Range −55°C to +125°C
Storage Temperature −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.
ADXL320
Rev. 0 | Page 5 of 16
PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
NC X
OUT
ST NC
COM Y
OUT
NC NC
COM COM COM NC
NC V
S
V
S
NC
NC = NO CONNEC
T
ADXL320
TOP VIEW
(Not to Scale)
04993-022
Figure 2. Pin Configuration
Table 3. Pin Function Descriptions
Pin No. Mnemonic Description
1 NC Do Not Connect
2 ST Self-Test
3 COM Common
4 NC Do Not Connect
5 COM Common
6 COM Common
7 COM Common
8 NC Do Not Connect
9 NC Do Not Connect
10 YOUT Y Channel Output
11 NC Do Not Connect
12 XOUT X Channel Output
13 NC Do Not Connect
14 VS2.4 V to 5.25 V
15 VS2.4 V to 5.25 V
16 NC Do Not Connect
ADXL320
Rev. 0 | Page 6 of 16
04993-002
t
P
t
L
t
25°C TO PEAK
t
S
PREHEAT
CRITICAL ZONE
T
L
TO T
P
TEMPERATURE
TIME
RAMP-DOWN
RAMP-UP
T
SMIN
T
SMAX
T
P
T
L
Figure 3. Recommended Soldering Profile
Table 4. Recommended Soldering Profile
Profile Feature Sn63/Pb37 Pb-Free
Average Ramp Rate (TL to TP) 3°C/second max 3°C/second max
Preheat
Minimum Temperature (TSMIN) 100°C 150°C
Maximum Temperature (TSMAX) 150°C 200°C
Time (TSMIN to TSMAX), tS 60 − 120 seconds 60 − 150 seconds
TSMAX to TL
Ramp-Up Rate 3°C/second 3°C/second
Time Maintained Above Liquidous (TL)
Liquidous Temperature (TL) 183°C 217°C
Time (tL) 60 − 150 seconds 60 − 150 seconds
Peak Temperature (TP) 240°C + 0°C/−5°C 260°C + 0°C/−5°C
Time within 5°C of Actual Peak Temperature (tP) 10 − 30 seconds 20 − 40 seconds
Ramp-Down Rate 6°C/second max 6°C/second max
Time 25°C to Peak Temperature 6 minutes max 8 minutes max
ADXL320
Rev. 0 | Page 7 of 16
TYPICAL PERFORMANCE CHARACTERISTICS (VS = 3.0 V)
25
0
5
10
15
20
1.40 1.42 1.44 1.46 1.48 1.50 1.52 1.54 1.56 1.58 1.60
04993-003
OUTPUT (V)
% OF POPULATION
Figure 4. X-Axis Zero g Bias Deviation from Ideal at 25°C
35
0
5
10
15
20
25
30
–2.8–2.4–2.0–1.6–1.2–0.8–0.4 0 0.4 0.8 1.2 1.6 2.0 2.4 2.8
04993-004
TEMPERATURE COEFFICIENT (mg/°C)
% OF POPULATION
Figure 5. X-Axis Zero g Bias Temperature Coefficient
90
0
10
20
30
40
50
70
80
60
164 184182180178176174172170168166
04993-005
SENSITIVITY (mV/g)
% OF POPULATION
Figure 6. X-Axis Sensitivity at 25°C
25
0
5
10
15
20
1.40 1.42 1.44 1.46 1.48 1.50 1.52 1.54 1.56 1.58 1.60
04993-006
OUTPUT (V)
% OF POPULATION
Figure 7. Y-Axis Zero g Bias Deviation from Ideal at 25°C
35
0
5
10
15
20
25
30
–2.8–2.4–2.0–1.6–1.2–0.8–0.4 0 0.4 0.8 1.2 1.6 2.0 2.4 2.8
04993-007
TEMPERATURE COEFFICIENT (mg/°C)
% OF POPULATION
Figure 8. Y-Axis Zero g Bias Temperature Coefficient
70
0
10
20
30
40
50
60
164 184182180178176174172170168166
04993-008
SENSITIVITY (mV/g)
% OF POPULATION
Figure 9. Y-Axis Sensitivity at 25°C
ADXL320
Rev. 0 | Page 8 of 16
1.54
1.53
1.52
1.51
1.50
1.49
1.48
1.47
1.46
–30 –20 –10 0 10 20 30 40 50 60 70 80
04993-009
TEMPERATURE (°C)
OUTPUT (SCALE = 174mV/g)
Figure 10. Zero g Bias vs. Temperature—Parts Soldered to PCB
35
30
25
20
15
10
5
0170 190 210 230 250 270 290 310 330 350
04993-010
NOISE ug/ Hz
% OF POPULATION
Figure 11. X-Axis Noise Density at 25°C
25
20
15
10
5
0–5–4–3–2–1012345
04993-011
PERCENT SENSITIVITY (%)
% OF POPULATION
Figure 12. Z vs. X Cross-Axis Sensitivity
0.180
0.170
0.171
0.172
0.173
0.174
0.175
0.176
0.177
0.178
0.179
–30 –20 –10 0 10 20 30 40 50 60 70 80
04993-012
TEMPERATURE (°C)
SENSITIVITY (V/g)
Figure 13. Sensitivity vs. Temperature—Parts Soldered to PCB
30
25
20
15
10
5
0170 190 210 230 250 270 290 310 330 350
04993-013
NOISE ug/ Hz
% OF POPULATION
Figure 14. Y-Axis Noise Density at 25°C
30
25
20
15
10
5
0–5–4–3–2–1012345
04993-014
PERCENT SENSITIVITY (%)
% OF POPULATION
Figure 15. Z vs. Y Cross-Axis Sensitivity
ADXL320
Rev. 0 | Page 9 of 16
60
50
40
30
20
10
035 7570656055504540
04993-015
SELF-TEST (mV)
% OF POPULATION
Figure 16. X-Axis Self-Test Response at 25°C
40
35
30
25
20
15
10
5
0420 430 440 450 460 470 480 490 500 510 520 530
04993-016
CURRENT (μA)
% OF POPULATION
Figure 17. Supply Current at 25°C
60
50
40
30
20
10
035 7570656055504540
04993-017
SELF-TEST (mV)
% OF POPULATION
Figure 18. Y-Axis Self-Test Response at 25°C
04993-020
Figure 19. Turn-On Time—CX, CY = 0.1 μF, Time Scale = 2 ms/DIV
ADXL320
Rev. 0 | Page 10 of 16
04993-018
X
OUT
= 1.500V
Y
OUT
= 1.500V
X
OUT
= 1.500V
Y
OUT
= 1.326V
X
OUT
= 1.326V
Y
OUT
= 1.500V
X
OUT
= 1.674V
Y
OUT
= 1.50V
X
OUT
= 1.500V
Y
OUT
= 1.674V
EARTH'S SURFACE
XL
320J
#1234
5678P
XL
320J
#1234
5678P
XL
320J
#1234
5678P
XL
320J
#1234
5678P
Figure 20. Output Response vs. Orientation
ADXL320
Rev. 0 | Page 11 of 16
THEORY OF OPERATION
The ADXL320 is a complete acceleration measurement system
on a single monolithic IC. The ADXL320 has a measurement
range of ±5 g. It 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 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 3 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.
ADXL320
Rev. 0 | Page 12 of 16
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
ADXL320 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 ADXL320 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.
Table 5. Filter Capacitor Selection, CX and CY
Bandwidth (Hz) Capacitor (μF)
1 4.7
10 0.47
50 0.10
100 0.05
200 0.027
500 0.01
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
315 mg (corresponding to 55 mV). This pin may be left open-
circuit or connected to common (COM) in normal use.
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.
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 ADXL320 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 ADXL320 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 ADXL320 is determined by
)1.6()μg/(250 ××= BWHzrmsNoise
At 100 Hz bandwidth the noise will be
mg3.2)1.6100()μg/(250 =××= HzrmsNoise
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
Peak-to-Peak Value
% of Time That Noise Exceeds
Nominal Peak-to-Peak Value
2 × rms 32
4 × rms 4.6
6 × rms 0.27
8 × rms 0.006
ADXL320
Rev. 0 | Page 13 of 16
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 ADXL320 for various CX and CY values.
Table 7. Filter Capacitor Selection (CX, CY)
Bandwidth
(Hz)
CX, CY
(μF)
RMS Noise
(mg)
Peak-to-Peak Noise
Estimate (mg)
10 0.47 1.0 6
50 0.1 2.25 13.5
100 0.047 3.2 18.9
500 0.01 7.1 42.8
USE WITH OPERATING VOLTAGES OTHER THAN 3 V
The ADXL320 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 5.25 V.
Note that some performance parameters change as the supply
voltage is varied.
The ADXL320 output is ratiometric, so the output sensitivity
(or scale factor) varies proportionally to supply voltage. At VS =
5 V, the output sensitivity is typically 312 mV/g. At VS = 2.4 V,
the output sensitivity is typically 135 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,
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 ADXL320 is
approximately 250 mV. At VS = 2.4 V, the self-test response is
approximately 25 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.
USE AS A DUAL-AXIS TILT SENSOR
Tilt measurement is one of the ADXL320’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 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 = 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.
ADXL320
Rev. 0 | Page 14 of 16
OUTLINE DIMENSIONS
16
5
13
8
9
12 1
4
0.65 BS C
2.43
1.75 S Q
1.08
1.95 BSC
0.20 M IN PIN 1
INDICATOR
BOTTOM
VIEW
0.20 M IN
SEATING
PLANE
1.50
1.45
1.40
PIN 1
INDI
C
ATOR TOP
VIEW
COPLANARITY
0.05
0.05 M A X
0.02 NOM
0.35
0.30
0.25
0.55
0.50
0.45
4.15
4.00 S Q
3.85
*STACKED DIE W ITH G LASS SEAL.
072606-A
Figure 21. 16-Lead Lead Frame Chip Scale Package [LFCSP_LQ]
4 mm × 4 mm Body
(CP-16-5a*)
Dimensions shown in millimeters
ORDERING GUIDE
Model
Measurement
Range
Specified
Voltage (V)
Temperature
Range Package Description
Package
Option
ADXL320JCP1±5 g 3 −20°C to +70°C 16-Lead LFCSP_LQ CP-16-5a
ADXL320JCP–REEL1±5 g 3 −20°C to +70°C 16-Lead LFCSP_LQ CP-16-5a
ADXL320JCP–REEL71±5 g 3 −20°C to +70°C 16-Lead LFCSP_LQ CP-16-5a
ADXL320EB Evaluation Board
1 Lead finish—Matte tin.
ADXL320
Rev. 0 | Page 15 of 16
NOTES
ADXL320
Rev. 0 | Page 16 of 16
NOTES
© 2007 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
D04993–0–6/07(0)
