ADXL50 ,Monolithic Accelerometer With Signal ConditioningGENERAL DESCRIPTION The ADXL50 is powered from a standard +5 V supply and isThe ADXL50 is a complet ..
ADXL50JH ,Monolithic Accelerometer With Signal ConditioningSPECIFICATIONS ADXL50J/AParameter Conditions Min Typ Max UnitsSENSOR INPUTMeasurement Range G ..
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AM28F010-120JI , 1 Megabit (128 K x 8-Bit) CMOS 12.0 Volt, Bulk Erase Flash Memory
AM28F010-120PI , 1 Megabit (128 K x 8-Bit) CMOS 12.0 Volt, Bulk Erase Flash Memory
AM28F010-150EC , 1 Megabit (128 K x 8-Bit) CMOS 12.0 Volt, Bulk Erase Flash Memory
AM28F010-150JI , 1 Megabit (128 K x 8-Bit) CMOS 12.0 Volt, Bulk Erase Flash Memory
AM28F010-150JI , 1 Megabit (128 K x 8-Bit) CMOS 12.0 Volt, Bulk Erase Flash Memory
AM28F010-150PI , 1 Megabit (128 K x 8-Bit) CMOS 12.0 Volt, Bulk Erase Flash Memory
ADXL50-ADXL50JH
Monolithic Accelerometer With Signal Conditioning
REV.B
Monolithic Accelerometer
With Signal Conditioning
FEATURES
Complete Acceleration Measurement System
on a Single Monolithic IC
Full-Scale Measurement Range: 650 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 (65 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 DESCRIPTIONThe 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.
ADXL50–SPECIFICATIONSPREAMPLIFIER OUTPUT
NOTES
1Alignment error is specified as the angle between the true and indicated axis of sensitivity, (see Figure 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 VPR output. This is the algebraic sum of the alignment and the inherent sensor sensitivity errors, (see Figure 2).Specification refers to the maximum change in parameter from its initial at +25°C to its worst case value at TMIN to TMAX.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 μF capacitor, refer to
Figure 22.
5Applying logic high to the self-test input has the effect of applying an acceleration of –52.6 g to the ADXL50.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.
(TA = TMIN to TMAX, TA = +258C for J Grade Only, VS = +5 V, @ Acceleration = 0 g,
unless otherwise noted)
ABSOLUTE MAXIMUM RATINGS*Acceleration (Any Axis, Unpowered for 0.5 ms) . . . . . .2000 g
Acceleration (Any Axis, Powered for 0.5 ms) . . . . . . . . . .500 g
+VS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .–0.3 V to +7.0 V
Output Short Circuit Duration
(VPR, VOUT, VREF 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 causepermanent 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
ORDERING GUIDE
PIN DESCRIPTIONVPR
VOUT
CONNECTION DIAGRAM
10-Header (TO-100)
CAUTIONESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000V 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.
ADXL50
Polarity of the Acceleration OutputThe 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 VPR output
pin. Note that the polarity will be reversed to a negative going
signal at the buffer amplifier output VOUT, due to its inverting
configuration.
Mounting ConsiderationsThere 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 MisalignmentThe 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
(AXYZ) which might act on the sensor, where AX is the compo-
nent of interest. To determine AX, first, the component of accel-
eration in the XY plane (AXY) is found using the cosine law:
AXY = AXYZ (cosθXY) then
AX = AXY (cosθX)
Therefore: Typical VPR = 19 mV/g (AXYZ) (cosθXY) cosθX
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
+1g
TAB
PIN 5Figure 1.Output Polarity at VPR
Figure 2a.Sensitive X and Transverse Z Axis
Figure 2b.Sensitive X and Transverse Y Axis
Figure 2c.A Vector Analysis of an Acceleration Acting
Upon the ADXL50 in Three Dimensions
Sensitivity:The output voltage change per g unit of accelera-
tion applied, specified at the VPR 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 VPR 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 VPR (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 thepackage axis of sensitivity and the plane of the package pin
circle. See Figure 2.
Figure 3.
ADXL50 Output. Bottom Trace: Reference Accelerometer
Output
Table I shows the percentage signals resulting from various θX
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 ResonancesA 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 (AXYZ).
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/s2, or 9.807 meters/s2.
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.
ADXL50–Typical CharacteristicsFigure 4.Normalized Sensitivity vs. Frequency
Figure 5.Linearity in Percent of Full Scale
Figure 6.–3 dB Bandwidth vs. Temperature at VPR
Figure 7.
Capacitor, C1
Figure 8.
Figure 9.
Figure 13.
Temperature
Figure 10.Change in Sensitivity vs. Supply Voltage
Figure 11.VPR 0 g PSRR vs. Frequency
Figure 12.0 g Bias Level vs. Temperature
ADXL50
THEORY OF OPERATIONThe ADXL50 is a complete acceleration measurement system
on a single monolithic IC. It contains a polysilicon surface-mi-
cro machined sensor and signal conditioning circuitry. The
ADXL50 is capable of measuring both positive and negative ac-
celeration to a maximum level of ±50 g.
Figure 16 is a simplified view of the ADXL50’s acceleration
sensor at rest. The actual structure of the sensor consists of 42
unit cells and a common beam. The differential capacitor sensor
consists of independent fixed plates and a movable “floating”
central plate which deflects in response to changes in relative
motion. The two capacitors are series connected, forming a ca-
pacitive divider with a common movable central plate. A force
balance technique counters any impeding deflection due to ac-
celeration and servos the sensor back to its 0 g position.
Figure 16.A Simplified Diagram of the ADXL50 Sensor at
Rest
Figure 17 shows the sensor responding to an applied accelera-
tion. When this occurs, the common central plate or “beam”
moves closer to one of the fixed plates while moving further
from the other. The sensor’s fixed capacitor plates are driven
deferentially by a 1 MHz square wave: the two square wave am-
plitudes are equal but are 180° out of phase from one another.
When at rest, the values of the two capacitors are the same and
therefore, the voltage output at their electrical center (i.e., at the
center plate) is zero.
When the sensor begins to move, a mismatch in the value of
their capacitance is created producing an output signal at the
central plate. The output amplitude will increase with the
amount of acceleration experienced by the sensor. Information
concerning the direction of beam motion is contained in the
phase of the signal with synchronous demodulation being used
to extract this information. Note that the sensor needs to be po-
sitioned so that the measured acceleration is along its sensitive
axis.
Figure 18 shows a block diagram of the ADXL50. The voltage
output from the central plate of the sensor is buffered and then
applied to a synchronous demodulator. The demodulator is also
demodulator will rectify any voltage which is in sync with its
clock signal. If the applied voltage is in sync and in phase with
the clock, a positive output will result. If the applied voltage is in
sync but 180° out of phase with the clock, then the demodu-
lator’s output will be negative. All other signals will be rejected.
An external capacitor, C1, sets the bandwidth of the demodulator.
The output of the synchronous demodulator drives the preamp
—an instrumentation amplifier buffer which is referenced to
+1.8 volts. The output of the preamp is fed back to the sensor
through a 3 MΩ isolation resistor. The correction voltage re-
quired to hold the sensor’s center plate in the 0 g position is a
direct measure of the applied acceleration and appears at the
VPR pin.
Figure 17.
to an Externally Applied Acceleration
When the ADXL50 is subjected to an acceleration, its capacitive
sensor begins to move creating a momentary output signal. This
is signal conditioned and amplified by the demodulator and
preamp circuits. The dc voltage appearing at the preamp output
is then fed back to the sensor and electrostatically forces the
center plate back to its original center position.
At 0 g the ADXL50 is calibrated to provide +1.8 volts at the
VPR pin. With an applied acceleration, the VPR voltage changes
to the voltage required to hold the sensor stationary for the du-
ration of the acceleration and provides an output which varies
directly with applied acceleration.
The loop bandwidth corresponds to the time required to apply
feedback to the sensor and is set by external capacitor C1. The
loop response is fast enough to follow changes in g level up to
and exceeding 1 kHz. The ADXL50’s ability to maintain a flat
response over this bandwidth keeps the sensor virtually motion-
less. This essentially eliminates any nonlinearity or aging effects
due to the sensor beam’s mechanical spring constant, as com-
pared to an open-loop sensor.
An uncommitted buffer amplifier provides the capability to ad-
just the scale factor and 0 g offset level over a wide range. An in-
ternal reference supplies the necessary regulated voltages for
powering the chip and +3.4 volts for external use.
