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ADXL320
Datasheet (Analog Devices)
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Datasheet ADXL320 Datasheet (Analog Devices)

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Page 1

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 V 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
= 2.4 V (typ)
S
Small and Thin ±5 g Accelerometer
ADXL320

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 C
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.
and CY at the X
X
OUT
and Y
pins. Bandwidths of
OUT

FUNCTIONAL BLOCK DIAGRAM

+3V
V
S
ADXL320
C
DC
SENSOR
COM ST
Rev. 0
AC
AMP
DEMOD
Figure 1.
OUTPUT
AMP
R
FILT
32kΩ
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781.329.4700 Fax: 781.326.8703 © 2004 Analog Devices, Inc. All rights reserved.
OUTPUT
AMP
R
FILT
32kΩ
Y
OUT
C
Y
X
OUT
C
X
04993-001
www.analog.com
Page 2
ADXL320

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
REVISION HISTORY
9/04—Revision 0: Initial Version
Setting the Bandwidth Using CX and CY................................. 12
Self-Test ....................................................................................... 12
Design Trade-Offs for Selecting Filter Characteristics: The Noise/BW Trade-Off
Use with Operating Voltages Other than 3 V............................. 13
Use as a Dual-Axis Tilt Sensor ................................................. 13
Outline Dimensions....................................................................... 14
Ordering Guide .......................................................................... 14
.................................................................. 12
Rev. 0 | Page 2 of 16
Page 3
ADXL320
, Y
, Y
OUT
OUT
OUT
4
, Y
1
2
OUT
g
Each axis VS = 3 V 156 174 192 mV/g
3
VS = 3 V 0.01 %/°C
VS = 3 V 1.3 1.5 1.7 V
0.002 10 µF
Self-test 0 to 1 55 mV
20 ms

SPECIFICATIONS

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
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)
Sensitivity at X
Sensitivity Change due to Temperature ZERO g BIAS LEVEL (RATIOMETRIC) Each axis
0 g Voltage at X
0 g Offset Versus Temperature ±0.6 mg/°C NOISE PERFORMANCE
Noise Density @ 25°C 250 µg/√Hz rms FREQUENCY RESPONSE
CX, CY Range
R
Tolerance 32 ± 15% kΩ
FILT
Sensor Resonant Frequency 5.5 kHz SELF-TEST
Logic Input Low 0.6 V
Logic Input High 2.4 V
ST Input Resistance to Ground 50 kΩ
Output Change at X 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 Time TEMPERATURE
Operating Temperature Range −20 70 °C
OUT
OUT
5
6
7
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.
Rev. 0 | Page 3 of 16
Page 4
ADXL320

ABSOLUTE MAXIMUM RATINGS

Table 2.
Parameter Rating
Acceleration (Any Axis, Unpowered) 10,000 g Acceleration (Any Axis, Powered) 10,000 g V
S
All Other Pins
Output Short-Circuit Duration (Any Pin to Common) Indefinite
Operating Temperature Range −55°C to +125°C Storage Temperature −65°C to +150°C
−0.3 V to +7.0 V (COM − 0.3 V) to
+ 0.3 V)
(V
S

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.
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 16
Page 5
ADXL320
T

PIN CONFIGURATION AND FUNCTION DESCRIPTIONS

NC VSVSNC
NC X
ST
COM
NC NC
NC = NO CONNEC
ADXL320
TOP VIEW
(Not to Scale)
COM COM COM NC
Figure 2. Pin Configuration
NC
Y
OUT
OUT
04993-022
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 Y
OUT
Y Channel Output 11 NC Do Not Connect 12 X
OUT
X Channel Output 13 NC Do Not Connect 14 V 15 V
S
S
2.4 V to 5.25 V
2.4 V to 5.25 V
16 NC Do Not Connect
Rev. 0 | Page 5 of 16
Page 6
ADXL320
T
P
T
L
T
TEMPERATURE
SMIN
T
SMAX
t
S
PREHEAT
RAMP-UP
t
P
t
RAMP-DOWN
CRITICAL ZONE
L
T
TO T
L
P
t
25°C TO PEAK
TIME
04993-002
Figure 3. Recommended Soldering Profile
Table 4. Recommended Soldering Profile
Profile Feature Sn63/Pb37 Pb-Free
Average Ramp Rate (TL to TP) 3°C/s max 3°C/s max Preheat Minimum Temperature (T Minimum Temperature (T Time (T T
SMAX
to T
SMIN
L
to T
SMAX
), t
) 100°C 150°C
SMIN
) 150°C 200°C
SMAX
S
60 s − 120 s 60 s − 150 s
Ramp-Up Rate 3°C/s 3°C/s Time Maintained Above Liquidous (TL) Liquidous Temperature (TL) 183°C 217°C Time (tL) 60 s − 150 s 60 s − 150 s 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 s − 30 s 20 s − 40 s Ramp-Down Rate 6°C/s max 6°C/s max Time 25°C to Peak Temperature 6 min max 8 min max
Rev. 0 | Page 6 of 16
Page 7
ADXL320

TYPICAL PERFORMANCE CHARACTERISTICS (VS = 3.0 V)

25
25
20
15
10
% OF POPULATION
5
0
1.40 1.42 1.44 1.46 1.48 1.50 1.52 1.54 1.56 1.58 1.60 OUTPUT (V)
Figure 4. X-Axis Zero g Bias Deviation from Ideal at 25°C
35
30
25
20
15
% OF POPULATION
10
5
04993-003
20
15
10
% OF POPULATION
5
0
1.40 1.42 1.44 1.46 1.48 1.50 1.52 1.54 1.56 1.58 1.60 OUTPUT (V)
Figure 7. Y-Axis Zero g Bias Deviation from Ideal at 25°C
35
30
25
20
15
% OF POPULATION
10
5
04993-006
0
–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
TEMPERATURE COEFFICIENT (mg/°C)
Figure 5. X-Axis Zero g Bias Temperature Coefficient
90
80
70
60
50
40
30
% OF POPULATION
20
10
0
164 184182180178176174172170168166
SENSITIVITY (mV/g)
Figure 6. X-Axis Sensitivity at 25°C
04993-004
04993-005
0
–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
TEMPERATURE COEFFICIENT (mg/°C)
Figure 8. Y-Axis Zero g Bias Temperature Coefficient
70
60
50
40
30
% OF POPULATION
20
10
0
164 184182180178176174172170168166
SENSITIVITY (mV/g)
Figure 9. Y-Axis Sensitivity at 25°C
04993-007
04993-008
Rev. 0 | Page 7 of 16
Page 8
ADXL320
1.54
1.53
1.52
1.51
1.50
1.49
1.48
OUTPUT (SCALE = 174mV/g)
1.47
1.46 –30 –20 –10 0 10 20 30 40 50 60 70 80
Figure 10. Zero g Bias vs. Temperature—Parts Soldered to PCB
35
TEMPERATURE (°C)
04993-009
0.180
0.179
0.178
0.177
0.176
0.175
0.174
SENSITIVITY (V/g)
0.173
0.172
0.171
0.170 –30 –20 –10 0 10 20 30 40 50 60 70 80
TEMPERATURE (°C)
Figure 13. Sensitivity vs. Temperature—Parts Soldered to PCB
30
04993-012
30
25
20
15
% OF POPULATION
10
5
0
170 190 210 230 250 270 290 310 330 350
NOISE ug/ Hz
Figure 11. X-Axis Noise Density at 25°C
25
20
15
10
% OF POPULATION
5
04993-010
25
20
15
10
% OF POPULATION
5
0
170 190 210 230 250 270 290 310 330 350
NOISE ug/ Hz
Figure 14. Y-Axis Noise Density at 25°C
30
25
20
15
10
% OF POPULATION
5
04993-013
0
–5–4–3–2–1012345
PERCENT SENSITIVITY (%)
Figure 12. Z vs. X Cross-Axis Sensitivity
04993-011
Rev. 0 | Page 8 of 16
0
–5–4–3–2–1012345
PERCENT SENSITIVITY (%)
Figure 15. Z vs. Y Cross-Axis Sensitivity
04993-014
Page 9
ADXL320
60
60
% OF POPULATION
% OF POPULATION
50
40
30
20
10
0
35 7570656055504540
SELF-TEST (mV)
Figure 16. X-Axis Self-Test Response at 25°C
40
35
30
25
20
15
10
04993-015
% OF POPULATION
50
40
30
20
10
0
35 7570656055504540
SELF-TEST (mV)
Figure 18. Y-Axis Self-Test Response at 25°C
04993-017
5
04993-020
0
420 430 440 450 460 470 480 490 500 510 520 530
CURRENT (µA)
04993-016
Figure 19. Turn-On Time—C
, CY = 0.1 µF, Time Scale = 2 ms/DIV
X
Figure 17. Supply Current at 25°C
Rev. 0 | Page 9 of 16
Page 10
ADXL320
X Y
OUT
OUT
= 1.500V = 1.674V
XL
X
= 1.326V
5678P #1234
320J
XL
Y
X Y
OUT
OUT
OUT
OUT
= 1.500V
5678P
= 1.674V = 1.50V
#1234
320J
X
= 1.500V
XL
OUT
= 1.326V
Y
OUT
X
= 1.500V
OUT
= 1.500V
Y
OUT
320J #1234 5678P
XL
320J
#1234
5678P
EARTH'S SURFACE
04993-018
Figure 20. Output Response vs. Orientation
Rev. 0 | Page 10 of 16
Page 11
ADXL320

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 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 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.
Rev. 0 | Page 11 of 16
Page 12
ADXL320

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 C
SETTING THE BANDWIDTH USING CX AND C
The ADXL320 has provisions for band-limiting the X Y
pins. Capacitors must be added at these pins to implement
OUT
low-pass filtering for antialiasing and noise reduction. The equation for the 3 dB bandwidth is
= 1/(2π(32 kΩ) × C
F
−3 dB
(X, Y)
)
or more simply,
= 5 µF/C
F
–3 dB
The tolerance of the internal resistor (R
(X, Y)
) typically varies as
FILT
much as ±15% of its nominal value (32 kΩ), and the bandwidth varies accordingly. A minimum capacitance of 2000 pF for C
is required in all cases.
and C
Y
Table 5. Filter Capacitor Selection, C
and C
X
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
, an electrostatic force is exerted on the accelerometer beam.
V
S
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
+ 0.3 V. If this cannot be guaranteed due to the system design
V
S
(for instance, if there are multiple supply voltages), then a low
clamping diode between ST and VS is recommended.
V
F
.
DC
Y
and
OUT
X
Y
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 X
OUT
and Y
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
At 100 Hz bandwidth the noise will be
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
% of Time That Noise Exceeds
Peak-to-Peak Value
Nominal Peak-to-Peak Value
2 × rms 32 4 × rms 4.6 6 × rms 0.27 8 × rms 0.006
OUT
.
)1.6()µg/(250 ××= BWHzrmsNoise
mg3.2)1.6100()µg/(250 =××= HzrmsNoise
Rev. 0 | Page 12 of 16
Page 13
ADXL320
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 C
and CY values.
X
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 V 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 V the output sensitivity is typically 312 mV/g. At V output sensitivity is typically 135 mV/g.
The zero g bias output is also ratiometric, so the zero g output is nominally equal to V
as low as 2.4 V or as high as 5.25 V. Note
S
= 5 V,
S
= 2.4 V, the
S
/2 at all supply voltages.
S

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(A
/1 g)
X
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 V density is typically 150 µg/√Hz, while at V
= 5 V, the noise
S
= 2.4 V, the noise
S
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 V approximately 250 mV. At V
= 5 V, the self-test response for the ADXL320 is
S
= 2.4 V, the self-test response is
S
approximately 25 mV.
The supply current decreases as the supply voltage decreases. Typical current consumption at V current consumption at V
= 2.4 V is 350 µA.
S
= 5 V is 750 µA, and typical
S
ROLL = ASIN(A
/1 g)
Y
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.
Rev. 0 | Page 13 of 16
Page 14
ADXL320
R

OUTLINE DIMENSIONS

PIN 1
INDICATO
1.50
1.45
1.40 SEATING PLANE
TOP
VIEW
0.35
0.30
0.25
0.20 MIN
4.15
4.00 SQ
3.85
0.65 BSC
0.05 MAX
0.02 NOM
COPLANARITY
0.05
0.55
0.50
0.45
12
9
0.20 MIN
13
BOTTOM
VIEW
8
Figure 21. 16-Lead Lead Frame Chip Scale Package [LFCSP]
4 mm × 4 mm Body (CP-16-5)
Dimensions shown in millimeters

ORDERING GUIDE

Measurement
Model
ADXL320JCP
1
Range
±5 g 3 −20°C to +70°C 16-Lead LFCSP CP-16-5 ADXL320JCP–REEL1 ±5 g 3 −20°C to +70°C 16-Lead LFCSP CP-16-5 ADXL320JCP–REEL71 ±5 g 3 −20°C to +70°C 16-Lead LFCSP CP-16-5 ADXL320EB Evaluation Board
Specified Voltage (V)
Temperature Range Package Description
16
5
1
4
1.95 BSC
PIN 1 INDICATOR
2.43
1.75 SQ
1.08
Package Option
1
Lead finish—Matte tin.
Rev. 0 | Page 14 of 16
Page 15
ADXL320
NOTES
Rev. 0 | Page 15 of 16
Page 16
ADXL320
NOTES
© 2004 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners.
D04993–0–9/04(0)
Rev. 0 | Page 16 of 16
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