Dual-Axis, High-g,
iMEMS® Accelerometers
ADXL278
FEATURES
GENERAL DESCRIPTION
Complete dual-axis acceleration measurement system on a
single monolithic IC
Available in ±35 g/±35 g, ±50 g/±50 g, or ±70 g/±35 g output
full-scale ranges
Full differential sensor and circuitry for high resistance to
EMI/RFI
Environmentally robust packaging
Complete mechanical and electrical self-test on digital
command
Output ratiometric to supply
Sensitive axes in the plane of the chip
High linearity (0.2% of full scale)
Frequency response down to dc
Low noise
Low power consumption
Tight sensitivity tolerance and 0 g offset capability
Largest available prefilter clipping headroom
400 Hz, 2-pole Bessel filter
Single-supply operation
Compatible with Sn/Pb and Pb-free solder processes
Qualified for automotive applications
The ADXL278 is a low power, complete, dual-axis
accelerometer with signal conditioned voltage outputs that are
on a single monolithic IC. This product measures acceleration
with a full-scale range of (X-axis/Y-axis) ±35 g/±35 g, ±50 g/
±50 g, or ±70 g/±35 g (minimum). The ADXL278 can also
measure both dynamic acceleration (vibration) and static
acceleration (gravity).
The ADXL278 is the fourth-generation surface micromachined
iMEMS® accelerometer from ADI with enhanced performance
and lower cost. Designed for use in front and side impact airbag
applications, this product also provides a complete costeffective solution useful for a wide variety of other applications.
The ADXL278 is temperature stable and accurate over the
automotive temperature range, with a self-test feature that fully
exercises all the mechanical and electrical elements of the sensor
with a digital signal applied to a single pin.
The ADXL278 is available in a 5 mm × 5 mm × 2 mm,
8-terminal ceramic LCC package.
APPLICATIONS
Vibration monitoring and control
Vehicle collision sensing
Shock detection
FUNCTIONAL BLOCK DIAGRAM
ADXL278
EXC
DIFFERENTIAL
SENSOR
DEMOD
AMP
400Hz
BESSEL
FILTER
XOUT
DEMOD
AMP
400Hz
BESSEL
FILTER
YOUT
VS
VDD
VDD2
EXC
DIFFERENTIAL
SENSOR
SELF-TEST
05365-001
TIMING
GENERATOR
VDD3
Figure 1.
Rev. B
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.
www.analog.com
Tel: 781.329.4700
Fax: 781.461.3113
©2010 Analog Devices, Inc. All rights reserved.
ADXL278* Product Page Quick Links
Last Content Update: 11/01/2016
Comparable Parts
Design Resources
View a parametric search of comparable parts
•
•
•
•
Documentation
Application Notes
• AN-652: Considerations for Soldering Accelerometers in
LCC-8 Packages onto Printed Circuit Boards
• AN-688: Phase and Frequency Response of iMEMS®
Accelerometers and Gyros
Data Sheet
• ADXL278: Dual-Axis, High-g, iMEMS® Accelerometers
Data Sheet
ADXL278 Material Declaration
PCN-PDN Information
Quality And Reliability
Symbols and Footprints
Discussions
View all ADXL278 EngineerZone Discussions
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Technical Support
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number
* This page was dynamically generated by Analog Devices, Inc. and inserted into this data sheet. Note: Dynamic changes to
the content on this page does not constitute a change to the revision number of the product data sheet. This content may be
frequently modified.
ADXL278
TABLE OF CONTENTS
Features .............................................................................................. 1
Theory of Operation .........................................................................7
Applications ....................................................................................... 1
Applications........................................................................................8
General Description ......................................................................... 1
Power Supply Decoupling ............................................................8
Functional Block Diagram .............................................................. 1
Self-Test ..........................................................................................8
Revision History ............................................................................... 2
Clock Frequency Supply Response .............................................8
Specifications..................................................................................... 3
Signal Distortion ...........................................................................8
Absolute Maximum Ratings ............................................................ 4
Outline Dimensions ..........................................................................9
ESD Caution .................................................................................. 4
ADXL278 Ordering Guide ...........................................................9
Pin Configuration and Function Descriptions ............................. 5
Automotive Products ....................................................................9
REVISION HISTORY
8/10—Rev. A to Rev. B
Updated Format .................................................................. Universal
Change to Features Section ............................................................. 1
Updated Outline Dimensions ......................................................... 9
Changes to Ordering Guide ............................................................ 9
Added Automotive Products Section............................................. 9
7/02—Rev. D to Rev. E
Edits to Features ................................................................................ 1
5/05—Rev. 0 to Rev. A
Rev. B | Page 2 of 12
ADXL278
SPECIFICATIONS1
At TA = −40°C to +105°C, 5.0 V dc ± 5%, acceleration = 0 g, unless otherwise noted.
Table 1.
Parameter
SENSOR
Output Full-Scale Range
Nonlinearity
Package Alignment Error
Sensor-to-Sensor
Alignment Error
Cross-Axis Sensitivity
Resonant Frequency
Sensitivity, Ratiometric
(Over Temperature)
OFFSET
Zero-g Output Voltage
(Over Temperature)2
NOISE
Noise Density
Clock Noise
FREQUENCY RESPONSE
−3 dB Frequency
−3 dB Frequency Drift
SELF-TEST
Output Change
(Cube vs. VDD)3
Logic Input High
Logic Input Low
Input Resistance
OUTPUT AMPLIFIER
Output Voltage Swing
Conditions
Model No. AD22284
Min
Typ Max
Model No. AD22285
Min
Typ Max
Model No. AD22286
Axis Min
Typ Max
IOUT ≤ ±100 µA
37
55
X
Y
0.2
1
0.1
−5
VDD = 5 V,
100 Hz
VOUT − VDD/2,
VDD = 5 V
52.25
10 Hz − 400 Hz,
5V
+150
0.2
1
0.1
−5
36.1
3
2
0.2
1
0.1
+5
24
38
−150
39.9
+150
1.4
5
3
−5
2
+5
g
g
%
Degree
Degree
28.35
%
kHz
mV/g
57.75
mV/g
X
25.65
24
27
Y
52.25
55
X
−100
+100
mV
Y
−150
+150
mV
X
1.8
3.5
mg/√Hz
Y
1.1
5
3
mg/√Hz
mV p-p
360
400
2
440
Hz
Hz
X
216
270
324
mV
Y
440
3.5
550
660
30
50
mV
V
V
kΩ
5
2-pole Bessel
360
400
2
440
360
400
2
440
VDD = 5 V
440
550
660
304
380
456
VDD = 5 V
VDD = 5 V
Pull-down
resistor to GND
3.5
25°C to
TMIN or TMAX
IOUT = ±400 µA
3.5
1
30
50
4.75
3.5
1
30
0.25
POWER SUPPLY (VDD)
Functional Range
Quiescent Supply Current
TEMPERATURE RANGE
3
57.75
1.1
1000
2
+5
24
55
−150
Capacitive Load Drive
PREFILTER HEADROOM
CFSR @ 400 kHz
1
2
70
37
Unit
VDD −
0.25
0.25
2.2
−40
VDD −
0.25
1000
280
6
VDD = 5 V
50
1
0.25
1000
400
4.5
5.25
6
2.9
+105
4.75
3.5
2.2
−40
All minimum and maximum specifications are guaranteed. Typical specifications are not guaranteed.
Zero g output is ratiometric.
Self-test output at VDD = (Self-Test Output at 5 V) × (VDD/5 V)3.
Rev. B | Page 3 of 12
VDD −
0.25
560
3
6
5.25
6
2.9
+105
4.75
3.5
2.2
−40
5.25
6
2.9
+105
V
pF
g
V/V
V/V
V
V
mA
°C
ADXL278
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
4,000 g
4,000 g
−0.3 V to +7.0 V
(COM − 0.3 V) to
(VS + 0.3 V)
Indefinite
−65°C to +150°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
Rev. B | Page 4 of 12
ADXL278
PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
VDD2
8
VDD3 1
YOUT 2
COM 3
7
VDD
ADXL278
6 XOUT
TOP VIEW
(Not to Scale)
5 NC
05365-002
4
ST
NC = NO CONNECT
Figure 2. Pin Configuration
Table 3. Pin Function Descriptions
Pin No.
1
2
3
4
5
6
7
8
Mnemonic
VDD3
YOUT
COM
ST
NC
XOUT
VDD
VDD2
Description
3.5 V to 6 V
Y Channel Output
Common
Self-Test
Do Not Connect
X Channel Output
3.5 V to 6 V
3.5 V to 6 V
Rev. B | Page 5 of 12
ADXL278
CRITICAL ZONE
TL TO TP
tP
TP
TEMPERATURE
RAMP-UP
TL
tL
TSMAX
TSMIN
tS
RAMP-DOWN
05365-003
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)
Maximum 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
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
PIN 8
XXXXX
XXXX
22285
XXXXX
XXXX
22285
XOUT = 2.500V
YOUT = 2.462V
22285
XXXXX
XXXX
XOUT = 2.538V
YOUT = 2.500V
XOUT = 2.500V
YOUT = 2.500V
EARTH'S SURFACE
Figure 4. Output Response vs. Orientation
Rev. B | Page 6 of 12
05365-004
XOUT = 2.500V
YOUT = 2.538V
XXXXX
XXXX
22285
XOUT = 2.462V
YOUT = 2.500V
ADXL278
THEORY OF OPERATION
Complementary 200 kHz square waves drive the fixed plates.
Electrical feedback adjusts the amplitudes of the square waves
such that the ac signal on the moving plates is 0. The feedback
signal is linearly proportional to the applied acceleration. This
unique feedback technique ensures that there is no net
electrostatic force applied to the sensor. The differential
feedback control signal is also applied to the input of the filter,
where it is filtered and converted to a single-ended signal.
Rev. B | Page 7 of 12
MOVABLE
FRAME
PLATE
CAPACITORS
UNIT
SENSING
CELL
FIXED
PLATES
UNIT
FORCING
CELL
MOVING
PLATE
ANCHOR
Figure 5. Simplified View of Sensor Under Acceleration
05365-005
Figure 5 is a simplified view of one of the differential sensor
elements. Each sensor includes several differential capacitor
unit cells. Each cell is composed of fixed plates attached
to the substrate and movable plates attached to the frame.
Displacement of the frame changes the differential capacitance,
which is measured by the on-chip circuitry.
ANCHOR
ACCELERATION
The ADXL278 provides a fully differential sensor structure and
circuit path, resulting in the industry’s highest resistance to
EMI/RFI effects. This latest generation uses electrical feedback
with zero-force feedback for improved accuracy and stability.
The sensor resonant frequency is significantly higher than the
signal bandwidth set by the on-chip filter, avoiding the signal
analysis problems caused by resonant peaks near the signal
bandwidth.
ADXL278
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 200 kHz internal clock frequency (or any harmonic
thereof), noise on the supply can cause interference on the
ADXL278’s output. If additional decoupling is needed, a 50 Ω
(or smaller) resistor or ferrite bead cany be inserted in the
supply line. Additionally, a larger bulk bypass capacitor (in the
1 µF to 4.7 µF range) can be added in parallel to CDC.
SELF-TEST
The fixed fingers in the forcing cells are normally kept at the
same potential as that of the movable frame. When the self-test
digital input is activated, the voltage on the fixed fingers on one
side of the moving plate in the forcing cells is changed. This
creates an attractive electrostatic force, which causes the frame
to move towards those fixed fingers. The entire signal channel is
active; therefore, the sensor displacement causes a change in
VOUT. The ADXL278’s self-test function is a comprehensive
method of verifying the operation of the accelerometer.
Because electrostatic force is independent of the polarity of the
voltage across capacitor plates, a positive voltage is applied in
half of the forcing cells, and its complement in the other half of
the forcing cells. Activating self-test causes a step function force
to be applied to the sensor, while the capacitive coupling term is
canceled. The ADXL278 has improved self-test functionality,
including excellent transient response and high speed switching
capabilities. Arbitrary force waveforms can be applied to the
sensor by modulating the self-test input, such as test signals to
measure the system frequency response or even crash signals to
verify algorithms within the limits of the self-test swing.
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.
CLOCK FREQUENCY SUPPLY RESPONSE
In any clocked system, power supply noise near the clock
frequency may have consequences at other frequencies. An
internal clock typically controls the sensor excitation and the
signal demodulator for micromachined accelerometers.
If the power supply contains high frequency spikes, they may be
demodulated and interpreted as an acceleration signal. A signal
appears as the difference between the noise frequency and the
demodulator frequency. If the power supply spikes are 100 Hz
away from the demodulator clock, there is an output term at
100 Hz. If the power supply clock is at exactly the same frequency
as the accelerometer clock, the term appears as an offset.
If the difference frequency is outside of the signal bandwidth,
the filter attenuates it. However, both the power supply clock
and the accelerometer clock may vary with time or temperature,
which can cause the interference signal to appear in the output
filter bandwidth.
The ADXL278 addresses this issue in two ways. First, the high
clock frequency eases the task of choosing a power supply clock
frequency such that the difference between it and the accelerometer clock remains well outside of the filter bandwidth.
Second, the ADXL278 is the only micromachined accelerometer
to have a fully differential signal path, including differential
sensors. The differential sensors eliminate most of the power
supply noise before it reaches the demodulator. Good high
frequency supply bypassing, such as a ceramic capacitor close to
the supply pins, also minimizes the amount of interference.
The clock frequency supply response (CFSR) is the ratio of the
response at VOUT to the noise on the power supply near the
accelerometer clock frequency. A CFSR of 3 means that the
signal at VOUT is 3× the amplitude of an excitation signal at VDD
near the accelerometer internal clock frequency. This is
analogous to the power supply response, except that the
stimulus and the response are at different frequencies. The
ADXL278’s CFSR is 10× better than a typical single-ended
accelerometer system.
SIGNAL DISTORTION
Signals from crashes and other events may contain high
amplitude, high frequency components. These components
contain very little useful information and are reduced by the
2-pole Bessel filter at the output of the accelerometer. However,
if the signal saturates at any point, the accelerometer output
does not look like a filtered version of the acceleration signal.
The signal may saturate anywhere before the filter. For example,
if the resonant frequency of the sensor is low, the displacement
per unit acceleration is high. The sensor may reach the
mechanical limit of travel if the applied acceleration is high
enough. This can be remedied by locating the accelerometer
where it does not see high values of acceleration and by using a
higher resonant frequency sensor, such as the ADXL278.
Also, the electronics may saturate in an overload condition
between the sensor output and the filter input. Ensuring that
internal circuit nodes operate linearly to at least several times
the full-scale acceleration value can minimize electrical
saturation. The ADXL278 circuit is linear to approximately 8×
full scale.
Rev. B | Page 8 of 12
ADXL278
OUTLINE DIMENSIONS
0.087
0.078
0.069
0.020
0.015
0.010
(R 4 PLCS)
7
0.180
0.177 SQ
0.174
0.028
0.020 DIA
0.012
1
0.106
0.100
0.094
0.075 REF
R 0.008
(8 PLCS)
0.008
0.006
0.004
TOP VIEW
R 0.008
(4 PLCS)
0.054
0.050
0.046
(PLATING OPTION 1,
SEE DETAIL A
FOR OPTION 2)
5
3
BOTTOM VIEW
0.077
0.070
0.063
0.019 SQ
DETAIL A
(OPTION 2)
05-21-2010-D
0.203
0.197 SQ
0.193
0.030
0.025
0.020
Figure 6. 8-Lead Ceramic Leadless Chip Carrier [LCC]
(E-8-1)
Dimensions shown in inches
ADXL278 ORDERING GUIDE
Model1, 2, 3
AD22284-A-R2
AD22284-A
ADW22284ZC
ADW22284ZC-RL7
AD22285-R2
AD22285
ADW22285ZC
ADW22285ZC-RL7
AD22286-R2
AD22286
ADW22286ZC
ADW22286ZC-RL7
1
2
3
Parts
per Reel
250
3,000
3,000
250
250
3,000
3,000
250
250
3,000
3,000
250
Measurement
Range
±35 g/±35 g
±35 g/±35 g
±35 g/±35 g
±35 g/±35 g
±50 g/±50 g
±50 g/±50 g
±50 g/±50 g
±50 g/±50 g
±70 g/±35 g
±70 g/±35 g
±70 g/±35 g
±70 g/±35 g
Specified
Voltage (V)
5
5
5
5
5
5
5
5
5
5
5
5
Temperature
Range
−40°C to +105°C
−40°C to +105°C
−40°C to +105°C
−40°C to +105°C
−40°C to +105°C
−40°C to +105°C
−40°C to +105°C
−40°C to +105°C
−40°C to +105°C
−40°C to +105°C
−40°C to +105°C
−40°C to +105°C
Package Description
8-Lead Ceramic Leadless Chip Carrier
8-Lead Ceramic Leadless Chip Carrier
8-Lead Ceramic Leadless Chip Carrier
8-Lead Ceramic Leadless Chip Carrier
8-Lead Ceramic Leadless Chip Carrier
8-Lead Ceramic Leadless Chip Carrier
8-Lead Ceramic Leadless Chip Carrier
8-Lead Ceramic Leadless Chip Carrier
8-Lead Ceramic Leadless Chip Carrier
8-Lead Ceramic Leadless Chip Carrier
8-Lead Ceramic Leadless Chip Carrier
8-Lead Ceramic Leadless Chip Carrier
Package
Option
E-8-1
E-8-1
E-8-1
E-8-1
E-8-1
E-8-1
E-8-1
E-8-1
E-8-1
E-8-1
E-8-1
E-8-1
All models are on tape and reel and are RoHS compliant parts.
Z = RoHS Compliant Part.
W = Qualified for Automotive Applications.
AUTOMOTIVE PRODUCTS
The ADW22284, ADW22285, and ADW22286 models are available with controlled manufacturing to support the quality and reliability
requirements of automotive applications. Note that these automotive models may have specifications that differ from the commercial
models; therefore, designers should review the Specifications section of this data sheet carefully. Only the automotive grade products
shown are available for use in automotive applications. Contact your local Analog Devices account representative for specific product
ordering information and to obtain the specific Automotive Reliability reports for these models.
Rev. B | Page 9 of 12
ADXL278
NOTES
Rev. B | Page 10 of 12
ADXL278
NOTES
Rev. B | Page 11 of 12
ADXL278
NOTES
©2010 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
D05365-0-8/10(B)
Rev. B | Page 12 of 12
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