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
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.
a
Monolithic Accelerometer
With Signal Conditioning
ADXL50*
FEATURES
Complete Acceleration Measurement System
on a Single Monolithic IC
Full-Scale Measurement Range: 50 g
Self-Test on Digital Command
+5 V Single Supply Operation
Sensitivity Precalibrated to 19 mV/g
Internal Buffer Amplifier for User Adjustable Sensitivity
and Zero-g Level
Frequency Response: DC to 10 kHz
Post Filtering with External Passive Components
High Shock Survival: >2000 g Unpowered
Other Versions Available: ADXL05 ( 5 g)
FUNCTIONAL BLOCK DIAGRAM
*Patents pending.
For convenience, the ADXL50 has an internal buffer amplifier
with a full 0.25 V to 4.75 V output range. This may be used to
set the zero-g level and change the output sensitivity by using
external resistors. External capacitors may be added to the resis-
tor network to provide 1 or 2 poles of filtering. No external
active components are required to interface directly to most
analog-to-digital converters (ADCs) or microcontrollers.
The ADXL50 uses a capacitive measurement method. The ana-
log output voltage is directly proportional to acceleration, and is
fully scaled, referenced and temperature compensated, resulting
in high accuracy and linearity over a wide temperature range.
Internal circuitry implements a forced-balance control loop that
improves accuracy by compensating for any mechanical sensor
variations.
The ADXL50 is powered from a standard +5 V supply and is
robust for use in harsh industrial and automotive environments
and will survive shocks of more than 2000 g unpowered.
The ADXL50 is available in a hermetic 10-pin TO-100 metal
can, specified over the 0
C to +70
C commercial, and 40
C to
+85
C industrial temperature ranges. Contact factory for avail-
ability of devices specified for operation over the 40
C to
+105
C automotive temperature range.
GENERAL DESCRIPTION
The ADXL50 is a complete acceleration measurement system on
a single monolithic IC. Three external capacitors and a +5 volt
power supply are all that is required to measure accelerations up
to
50 g. Device sensitivity is factory trimmed to 19 mV/g,
resulting in a full-scale output swing of
0.95 volts for a
50 g
applied acceleration. Its zero g output level is +1.8 volts.
A TTL compatible self-test function can electrostatically deflect
the sensor beam at any time to verify device functionality.
V
REF
OUTPUT
V
OUT
DEMODULATOR
REFERENCE
SENSOR
+1.8V
BUFFER
AMP
PREAMP
OSCILLATOR
ADXL50
C2
OSCILLATOR
DECOUPLING
CAPACITOR
SELF TEST
(ST)
C3
+5V
DEMODULATOR
CAPACITOR
C1
C1
COM
R1
V
PR
V
IN
R3
R2
+3.4V
4
7
5
1
2
3
8
10
9
6
Analog Devices, Inc., 1996
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 617/329-4700
Fax: 617/326-8703
ADXL50SPECIFICATIONS
ADXL50J/A
Parameter
Conditions
Min
Typ
Max
Units
SENSOR INPUT
Measurement Range
Guaranteed Full Scale
50
+50
g
Nonlinearity
Best Fit Straight Line, 50 g FS
0.2
% of FS
Alignment Error
1
1
Degrees
Transverse Sensitivity
2
2
%
SENSITIVITY
Initial Sensitivity at V
PR
+25
C
16.1
19.0
21.9
mV/g
Temperature Drift
3
0.75/1.0
% of Reading
ZERO g BIAS LEVEL
at V
PR
Initial Offset
1.55/1.60
1.80
2.05/2.00
V
vs. Temperature
3
15/35
mV
vs. Supply
V
S
= 4.75 V to 5.25 V
10
32
mV/V
NOISE PERFORMANCE
at V
PR
Voltage Noise Density
BW = 10 Hz to 1 kHz
6.6
12
mg/
Hz
Noise in 100 Hz Bandwidth
66
mg rms
Noise in 10 Hz Bandwidth
20
mg rms
FREQUENCY RESPONSE
3 dB Bandwidth
4
C1 = 0.022
F (See Figure 22)
800
1300
Hz
3 dB Bandwidth
4
C1 = 0.0068
F
10
kHz
Sensor Resonant Frequency
24
kHz
SELF TEST INPUT
Output Change at V
PR
5
ST Pin from Logic "0" to "1"
0.85
1.00
1.15
V
Logic "1" Voltage
2.0
V
Logic "0" Voltage
0.8
V
Input Resistance
To Common
50
k
+3.4 V REFERENCE
Output Voltage
3.350
3.400
3.450
V
Output Temperature Drift
3
10
mV
Power Supply Rejection
DC, V
S
= +4.75 V to +5.25 V
1
10
mV/V
Output Current
Sourcing
500
A
PREAMPLIFIER OUTPUT
Voltage Swing
0.25
V
S
1.4
V
Current Output
Source or Sink
30
80
A
Capacitive Load Drive
100
pF
BUFFER AMPLIFIER
Input Offset Voltage
6
Delta from Nominal 1.800 V
10
25
mV
Input Bias Current
5
20
nA
Open-Loop Gain
DC
80
dB
Unity Gain Bandwidth
200
kHz
Output Voltage Swing
I
OUT
=
100
A
0.25
V
S
0.25
V
Capacitive Load Drive
1000
pF
Power Supply Rejection
DC, V
S
= +4.75 V to +5.25 V
1
10
mV/V
POWER SUPPLY
Operating Voltage Range
4.75
5.25
V
Quiescent Supply Current
10
13
mA
TEMPERATURE RANGE
Operating Range J
0
+70
C
Specified Performance A
40
+85
C
Automotive Grade*
40
+125
C
NOTES
1
Alignment error is specified as the angle between the true and indicated axis of sensitivity, (see Figure 2).
2
Transverse sensitivity is measured with an applied acceleration that is 90
from the indicated axis of sensitivity. Transverse sensitivity is specified as the percent of
transverse acceleration that appears at the V
PR
output. This is the algebraic sum of the alignment and the inherent sensor sensitivity errors, (see Figure 2).
3
Specification refers to the maximum change in parameter from its initial at +25
C to its worst case value at T
MIN
to T
MAX
.
4
Frequency at which response is 3 dB down from dc response assuming an exact C1 value is used. Maximum recommended BW is 10 kHz using a 0.007
F capacitor, refer to
Figure 22.
5
Applying
logic high to the self-test input has the effect of applying an acceleration of 52.6 g to the ADXL50.
6
Input offset voltage is defined as the output voltage differential from 1.800 V when the amplifier is connected as a follower (i.e., Pins 9 and 10 tied together). The voltage at
Pin 9 has a temperature drift proportional to that of the 3.4 V reference.
*Contact factory for availability of automotive grade devices.
All min and max specifications are guaranteed. Typical specifications are not tested or guaranteed.
Specifications subject to change without notice.
(T
A
= T
MIN
to T
MAX
, T
A
= +25 C for J Grade Only, V
S
= +5 V, @ Acceleration = 0
g,
unless otherwise noted)
REV. B
2
ADXL50
REV. B
3
ABSOLUTE MAXIMUM RATINGS*
Acceleration (Any Axis, Unpowered for 0.5 ms) . . . . . . 2000 g
Acceleration (Any Axis, Powered for 0.5 ms) . . . . . . . . . . 500 g
+V
S
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.3 V to +7.0 V
Output Short Circuit Duration
(V
PR
, V
OUT
, V
REF
Terminals to Common) . . . . . . . Indefinite
Operating Temperature . . . . . . . . . . . . . . . . . 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; the functional
operation of the device at these or any other conditions above those indicated 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
JA
JC
Device Weight
10-Pin TO-100
130
C/W
30
C/W
5 Grams
ORDERING GUIDE
Temperature
Model
Range
ADXL50JH
0
C to +70
C
ADXL50AH
40
C to +85
C
PIN DESCRIPTION
+5 V
The power supply input pin.
C2
Connection for an external bypass capacitor (nominally
0.022
F) used to prevent oscillator switching noise
from interfering with other ADXL50 circuitry. Please
see the section on component selection.
C1
Connections for the demodulator capacitor, nominally
0.022
F. See the section on component selection for
application information.
COM The power supply common (or "ground") connection.
V
REF
Output of the internal 3.4 V voltage reference.
ST
The digital self-test input. It is both CMOS and TTL
compatible.
V
PR
The ADXL50 preamplifier output providing an output
voltage of 19 mV per g of acceleration.
V
OUT
Output of the uncommitted buffer amplifier.
V
IN
The inverting input of the uncommitted buffer amplifier.
CONNECTION DIAGRAM
10-Header (TO-100)
WARNING!
ESD SENSITIVE DEVICE
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 ADXL50 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.
5
6
7
8
9
10
1
2
3
4
AXIS OF
SENSITIVITY
5
6
7
8
9
10
1
2
3
4
AXIS OF
SENSITIVITY
V
IN
V
OUT
V
PR
ST
V
REF
COM
C2
C1
C1
+5V
TOP VIEW
AXIS OF SENSITIVITY IS ALONG
A LINE BETWEEN PIN 5 AND
THE TAB.
THE CASE OF THE METAL CAN
PACKAGE IS CONNECTED TO
PIN 5 (COMMON).
ARROW INDICATES DIRECTION
OF POSITIVE ACCELERATION
ALONG AXIS OF SENSITIVITY.
NOTES:
ADXL50
4
REV. B
Polarity of the Acceleration Output
The polarity of the ADXL50 output is shown in the Figure 1.
When oriented to the earth's gravity (and held in place), the
ADXL50 will experience an acceleration of +1 g. This corre-
sponds to a change of approximately +19 mV at the V
PR
output
pin. Note that the polarity will be reversed to a negative going
signal at the buffer amplifier output V
OUT
, due to its inverting
configuration.
Mounting Considerations
There are three main causes of measurement error when using
accelerometers. The first two are alignment and transverse sen-
sitivity errors. The third source of error is due to resonances or
vibrations of the sensor in its mounting fixture.
Errors Due to Misalignment
The ADXL50 is a sensor designed to measure accelerations that
result from an applied force. Because these forces act on the
sensor in a vector manner, the alignment of the sensor to the
force to be measured may be critical.
The ADXL50 responds to the component of acceleration on its
sensitive X axis. Figures 2a and 2b show the relationship be-
tween the sensitive "X" axis and the transverse "Z" and "Y"
axes as they relate to the TO-100 package.
Figure 2c describes a three dimensional acceleration vector
(A
XYZ
) which might act on the sensor, where A
X
is the compo-
nent of interest. To determine A
X
, first, the component of accel-
eration in the XY plane (A
XY
) is found using the cosine law:
A
XY
= A
XYZ
(cos
XY
) then
A
X
= A
XY
(cos
X
)
Therefore: Typical V
PR
= 19 mV/g (A
XYZ
) (cos
XY
) cos
X
Note that an ideal sensor will react to forces along or at angles
to its sensitive axis but will reject signals from its various trans-
verse axes, i.e., those exactly 90
from the sensitive "X" axis.
But even an ideal sensor will produce output signals if the trans-
verse signals are not exactly 90
to the sensitive axis. An accel-
eration that is acting on the sensor from a direction different
from the sensitive axis will show up at the ADXL50 output at a
reduced amplitude.
Table I. Ideal Output Signals for Off Axis Applied
Accelerations Disregarding Device Alignment and
Transverse Sensitivity Errors
% of Signal Appearing
Output in gs for a 50 g
X
at Output
Applied Acceleration
0
100%
50 (On Axis)
1
99 98%
49.99
2
99.94%
49.97
3
99.86%
49.93
5
99.62%
49.81
10
98.48%
49.24
30
86.60%
43.30
45
70.71%
35.36
60
50.00%
25.00
80
17.36%
8.68
85
8.72%
4.36
87
5.25%
2.63
88
3.49%
1.75
89
1.7%
0.85
90
0%
0.00 (Transverse Axis)
+1g
TAB
PIN 5
Figure 1. Output Polarity at V
PR
Z
Z
X
TRANSVERSE Z AXIS
SENSITIVE (X) AXIS
SIDE VIEW
X
TAB
PIN 5
Figure 2a. Sensitive X and Transverse Z Axis
TRANSVERSE Y AXIS
TOP VIEW
Y
X
Y
SENSITIVE (X) AXIS
X
TAB
PIN 5
Figure 2b. Sensitive X and Transverse Y Axis
x
xy
Y Axis
X Axis
Axy
Ax
Axyz
Z Axis
Figure 2c. A Vector Analysis of an Acceleration Acting
Upon the ADXL50 in Three Dimensions
ADXL50
REV. B
5
Sensitivity: The output voltage change per g unit of accelera-
tion applied, specified at the V
PR
pin in mV/g.
Sensitive Axis (X): The most sensitive axis of the accelerom-
eter sensor. Defined by a line drawn between the package tab
and Pin 5 in the plane of the pin circle. See Figures 2a and 2b.
Sensor Alignment Error: Misalignment between the
ADXL50's on-chip sensor and the package axis, defined by
Pin 5 and the package tab.
Total Alignment Error: Net misalignment of the ADXL50's
on-chip sensor and the measurement axis of the application.
This error includes errors due to sensor die alignment to the
package, and any misalignment due to installation of the sensor
package in a circuit board or module.
Transverse Acceleration: Any acceleration applied 90
to the
axis of sensitivity.
Transverse Sensitivity Error: The percent of a transverse ac-
celeration that appears at the V
PR
output. For example, if the
transverse sensitivity is 1%, then a +10 g transverse acceleration
will cause a 0.1 g signal to appear at V
PR
(1% of 10 g). Trans-
verse sensitivity can result from a sensitivity of the sensor to
transverse forces or from misalignment of the internal sensor to
its package.
Transverse Y Axis: The axis perpendicular (90
) to the pack-
age axis of sensitivity in the plane of the package pin circle. See
Figure 2.
Transverse Z Axis: The axis perpendicular (90
) to both the
package axis of sensitivity and the plane of the package pin
circle. See Figure 2.
10
90
100
0%
1V
0.5ms
0.5V
Figure 3. 500 g Shock Overload Recovery. Top Trace:
ADXL50 Output. Bottom Trace: Reference Accelerometer
Output
Table I shows the percentage signals resulting from various
X
angles. Note that small errors in alignment have a negligible
effect on the output signal. A 1
error will only cause a 0.02%
error in the signal. Note, however, that a signal coming 1
off of
the transverse axis (i.e., 89
off the sensitive axis) will still con-
tribute 1.7% of its signal to the output. Thus large transverse
signals could cause output signals as large as the signals of
interest.
Table I may also be used to approximate the effect of the
ADXL50's internal errors due to misalignment of the die to the
package. For example: a 1 degree sensor alignment error will
allow 1.7% of a transverse signal to appear at the output. In a
nonideal sensor, transverse sensitivity may also occur due to in-
herent sensor properties. That is, if the sensor physically moves
due to a force applied exactly 90
to its sensitive axis, then this
might be detected as an output signal, whereas an ideal sensor
would reject such signals. In every day use, alignment errors
may cause a small output peak with accelerations applied close
to the sensitive axis but the largest errors are normally due to
large accelerations applied close to the transverse axis.
Errors Due to Mounting Fixture Resonances
A common source of error in acceleration sensing is resonance
of the mounting fixture. For example, the circuit board that the
ADXL50 mounts to may have resonant frequencies in the same
range as the signals of interest. This could cause the signals
measured to be larger than they really are. A common solution
to this problem is to dampen these resonances by mounting the
ADXL50 near a mounting post or by adding extra screws to
hold the board more securely in place.
When testing the accelerometer in your end application, it is
recommended that you test the application at a variety of fre-
quencies in order to ensure that no major resonance problems
exist.
GLOSSARY OF TERMS
Acceleration: Change in velocity per unit time.
Acceleration Vector: Vector describing the net acceleration
acting upon the ADXL50 (A
XYZ
).
g: A unit of acceleration equal to the average force of gravity
occurring at the earth's surface. A g is approximately equal to
32.17 feet/s
2
, or 9.807 meters/s
2
.
Nonlinearity: The maximum deviation of the ADXL50 output
voltage from a best fit straight line fitted to a plot of acceleration
vs. output voltage, calculated as a % of the full-scale output
voltage (@ 50 g).
Resonant Frequency: The natural frequency of vibration of
the ADXL50 sensor's central plate (or "beam"). At its resonant
frequency of 24 kHz, the ADXL50's moving center plate has a
peak in its frequency response with a Q of 3 or 4.
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