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기능 +-5 g to +-50 g/ Low Noise/ Low Power/ Single/Dual Axis iMEMS Accelerometers
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ADXL250JQC 데이터시트, 핀배열, 회로
a ؎5 g to ؎50 g, Low Noise, Low Power,
Single/Dual Axis iMEMS® Accelerometers
ADXL150/ADXL250
FEATURES
Complete Acceleration Measurement System
on a Single Monolithic IC
80 dB Dynamic Range
Pin Programmable ؎50 g or ؎25 g Full Scale
Low Noise: 1 mg/Hz Typical
Low Power: <2 mA per Axis
Supply Voltages as Low as 4 V
2-Pole Filter On-Chip
Ratiometric Operation
Complete Mechanical & Electrical Self-Test
Dual & Single Axis Versions Available
Surface Mount Package
+VS
0.1F
FUNCTIONAL BLOCK DIAGRAMS
TP
(DO NOT CONNECT)
ADXL150
GAIN
AMP
SENSOR
CLOCK
+VS
2
DEMODULATOR
25k
5k
BUFFER
AMP
9
SELF-TEST
COM
OFFSET
NULL
TP
(DO NOT CONNECT)
X OFFSET
NULL
VOUT
GENERAL DESCRIPTION
The ADXL150 and ADXL250 are third generation ± 50 g sur-
face micromachined accelerometers. These improved replace-
ments for the ADXL50 offer lower noise, wider dynamic range,
reduced power consumption and improved zero g bias drift.
The ADXL150 is a single axis product; the ADXL250 is a fully
integrated dual axis accelerometer with signal conditioning on a
single monolithic IC, the first of its kind available on the com-
mercial market. The two sensitive axes of the ADXL250 are
orthogonal (90°) to each other. Both devices have their sensitive
axes in the same plane as the silicon chip.
The ADXL150/ADXL250 offer lower noise and improved
signal-to-noise ratio over the ADXL50. Typical S/N is 80 dB,
allowing resolution of signals as low as 10 mg, yet still providing
a ± 50 g full-scale range. Device scale factor can be increased
from 38 mV/g to 76 mV/g by connecting a jumper between
VOUT and the offset null pin. Zero g drift has been reduced to
0.4 g over the industrial temperature range, a 10× improvement
over the ADXL50. Power consumption is a modest 1.8 mA
per axis. The scale factor and zero g output level are both
+VS
0.1F
ADXL250
GAIN
AMP
SENSOR
25k
DEMODULATOR
5k
SENSOR
CLOCK
GAIN
AMP
5k
DEMODULATOR
25k
BUFFER
AMP
VOUTX
+VS
2
BUFFER
AMP
VOUTY
SELF-TEST
COM
Y OFFSET
NULL
ratiometric to the power supply, eliminating the need for a volt-
age reference when driving ratiometric A/D converters such as
those found in most microprocessors. A power supply bypass
capacitor is the only external component needed for normal
operation.
The ADXL150/ADXL250 are available in a hermetic 14-lead
surface mount cerpac package specified over the 0°C to +70°C
commercial and –40°C to +85°C industrial temperature ranges.
Contact factory for availability of devices specified over automo-
tive and military temperature ranges.
iMEMS is a registered trademark of Analog Devices, Inc.
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
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700
World Wide Web Site: http://www.analog.com
Fax: 781/326-8703
© Analog Devices, Inc., 1998




ADXL250JQC pdf, 반도체, 판매, 대치품
ADXL150/ADXL250
GLOSSARY OF TERMS
Acceleration: Change in velocity per unit time.
Acceleration Vector: Vector describing the net acceleration
acting upon the ADXL150/ADXL250.
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/s2 or 9.807 meters/s2.
Nonlinearity: The maximum deviation of the ADXL150/
ADXL250 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 (at 50 g).
Resonant Frequency: The natural frequency of vibration of
the ADXL150/ADXL250 sensor’s central plate (or “beam”). At
its resonant frequency of 24 kHz, the ADXL150/ADXL250’s
moving center plate has a slight peak in its frequency response.
Sensitivity: The output voltage change per g unit of accelera-
tion applied, specified at the VOUT pin in mV/g.
Total Alignment Error: Net misalignment of the ADXL150/
ADXL250’s on-chip sensor and the measurement axis of the
application. This error includes errors due to sensor die align-
ment 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
acceleration that appears at VOUT.
Transverse Axis: The axis perpendicular (90°) to the axis of
sensitivity.
Zero g Bias Level: The output voltage of the ADXL150/
ADXL250 when there is no acceleration (or gravity) acting
upon the axis of sensitivity. The output offset is the difference
between the actual zero g bias level and (VS/2).
Polarity of the Acceleration Output
The polarity of the ADXL150/ADXL250 output is shown in
Figure 1. When its sensitive axis is oriented to the earth’s gravity
(and held in place), it will experience an acceleration of +1 g.
This corresponds to a change of approximately +38 mV at the
output pin. Note that the polarity will be reversed if the package
is rotated 180°. The figure shows the ADXL250 oriented so that
its “X” axis measures +1 g. If the package is rotated 90° clock-
wise (Pin 14 up, Pin 1 down), the ADXL250’s “Y” axis will now
measure +1 g.
8 7 8 AY 7
AX
ADXL150
14 1
AX
ADXL250
14 1
Figure 2. Output Polarity
Acceleration Vectors
The ADXL150/ADXL250 is a sensor designed to measure
accelerations that result from an applied force. It responds to
the component of acceleration on its sensitive X axis (ADXL150)
or on both the “X” and “Y” axis (ADXL250).
–4– REV. 0

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ADXL250JQC 전자부품, 판매, 대치품
ADXL150/ADXL250
THEORY OF OPERATION
The ADXL150 and ADXL250 are fabricated using a propri-
etary surface micromachining process that has been in high
volume production since 1993. The fabrication technique uses
standard integrated circuit manufacturing methods enabling all
the signal processing circuitry to be combined on the same chip
with the sensor.
The surface micromachined sensor element is made by deposit-
ing polysilicon on a sacrificial oxide layer that is then etched
away leaving the suspended sensor element. Figure 14 is a
simplified view of the sensor structure. The actual sensor has
42 unit cells for sensing acceleration. The differential capacitor
sensor is composed of fixed plates and moving plates attached to
the beam that moves in response to acceleration. Movement of
the beam changes the differential capacitance, which is measured
by the on chip circuitry.
The sensor has 12-unit capacitance cells for electrostatically
forcing the beam during a self-test. Self-test is activated by the
user with a logic high on the self-test input pin. During a logic
high, an electrostatic force acts on the beam equivalent to
approximately 20% of full-scale acceleration input, and thus a
proportional voltage change appears on the output pin. When
activated, the self-test feature exercises both the entire mechani-
cal structure and the electrical circuitry.
PLATE
CAPACITANCES
BEAM
FIXED
PLATE
UNIT CELL
ANCHOR
Figure 14. Simplified View of Sensor Under Acceleration
All the circuitry needed to drive the sensor and convert the
capacitance change to voltage is incorporated on the chip requiring
no external components except for standard power supply decou-
pling. Both sensitivity and the zero-g value are ratiometric to
the supply voltage, so that ratiometeric devices following the
accelerometer (such as an ADC, etc.) will track the accelerom-
eter if the supply voltage changes. The output voltage (VOUT) is
a function of both the acceleration input (a) and the power
supply voltage (VS) as follows:
VOUT
=
VS/2
(Sensitivity
×
VS
5V
× a)
Both the ADXL150 and ADXL250 have a 2-pole Bessel switched-
capacitor filter. Bessel filters, sometimes called linear phase
filters, have a step response with minimal overshoot and a maxi-
mally flat group delay. The –3 dB frequency of the poles is
preset at the factory to 1 kHz. These filters are also completely
self-contained and buffered, requiring no external components.
MEASURING ACCELERATIONS LESS THAN 50 g
The ADXL150/ADXL250 require only a power supply bypass
capacitor to measure ±50 g accelerations. For measuring ± 50 g
accelerations, the accelerometer may be directly connected to an
ADC (see Figure 25). The device may also be easily modified to
measure lower g signals by increasing its output scale factor.
The scale factor of an accelerometer specifies the voltage change
of the output per g of applied acceleration. This should not be
confused with its resolution. The resolution of the device is the
lowest g level the accelerometer is capable of measuring. Resolu-
tion is principally determined by the device noise and the mea-
surement bandwidth.
The zero g bias level is simply the dc output level of the accelerom-
eter when it is not in motion or being acted upon by the earth’s
gravity.
Pin Programmable Scale Factor Option
In its normal state, the ADXL150/ADXL250’s buffer amplifier
provides an output scale factor of 38 mV/g, which is set by an
internal voltage divider. This gives a full-scale range of ± 50 g
and a nominal bandwidth of 1 kHz.
A factor-of-two increase in sensitivity can be obtained by con-
necting the VOUT pin to the offset null pin, assuming that it is
not needed for offset adjustment. This connection has the effect
of reducing the internal feedback by a factor of two, doubling
the buffer’s gain. This increases the output scale factor to 76 mV/g
and provides a ± 25 g full-scale range.
Simultaneously, connecting these two pins also increases the
amount of internal post filtering, reducing the noise floor and
changing the nominal 3 dB bandwidth of the ADXL150/
ADXL250 to 500 Hz. Note that the post filter’s “Q” will also
be reduced by a factor of 2 from 0.58 (Bessel response) to a
much gentler “Q” value of 0.41. The primary effect of this
change in “Q” is only at frequencies within two octaves of the
corner frequency; above this the two filter slopes are essentially
the same. In applications where a flat response up to 500 Hz is
needed, it is better to operate the device at 38 mV/g and use an
external post filter. Note also that connecting VOUT to the offset
pin adds a 30 kload from VOUT to VS/2. When swinging ± 2 V
at VOUT, this added load will consume ±60 µA of the ADXL150/
ADXL250’s 100 µA (typical) output current drive.
REV. 0
–7–

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ADXL250JQC

+-5 g to +-50 g/ Low Noise/ Low Power/ Single/Dual Axis iMEMS Accelerometers

Analog Devices
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