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PDF MXA2312A Data sheet ( Hoja de datos )
| Número de pieza | MXA2312A | |
| Descripción | Dual Axis Accelerometer | |
| Fabricantes | Memsic | |
| Logotipo |  |
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Low Cost, ±2 g Dual Axis
Accelerometer with Analog Outputs
FEATURES
Dual axis accelerometer fabricated on a monolithic CMOS IC
On-chip mixed mode signal processing
Resolution better than 2 milli-g
50,000 g shock survival rating
30 Hz bandwidth expandable to >160 Hz
2.70V to 5.25V single supply operation
Small (5mm x 5mm x 2mm) surface mount package
Continuous self test
Independent axis programmability (special order)
APPLICATIONS
Automotive – Vehicle Security/Active Suspension/ABS
HED Angle Control/Tilt Sensing
Security – Gas Line/Elevator/Fatigue Sensing
Office Equipment – Computer Peripherals/PDA’s/Mouse
Smart Pens/Cell Phones
Gaming – Joystick/RF Interface/Menu Selection/Tilt Sensing
White Goods – Spin/Vibration Control
GENERAL DESCRIPTION
The MXA2312A is a very low cost, dual axis accelerometer
fabricated on a standard, submicron CMOS process. The
MXA2312A measures acceleration with a full-scale range
of ±2 g and a sensitivity of 312mV/g at 25°C. (The
MEMSIC accelerometer product line extends from ±1 g to
±10 g with custom versions available above ±10 g.) It can
measure both dynamic acceleration (e.g., vibration) and
static acceleration (e.g., gravity). The MXA2312A design
is based on heat convection and requires no solid proof
mass. This eliminates stiction and particle problems
associated with competitive devices and provides shock
survival up to 50,000 g, leading to significantly lower
failure rates and lower loss due to handling during
assembly.
The MXA2312A provides an absolute analog output (ref.
other MEMSIC data sheets for ratiometric, analog or digital
outputs). The typical noise floor is 0.75 mg/ Hz allowing
Information furnished by MEMSIC is believed to be accurate and reliable.
However, no responsibility is assumed by MEMSIC 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 MEMSIC.
MXA2312A
Sck
(optional)
Internal
Oscillator
Temperature
Sensor
CLK
Voltage
Reference
Heater
Control
Continous
Self Test
X axis
Low Pass
Filter
Factory Adjust
Offset & Gain
2-AXIS
SENSOR
Y axis
Vdd
Gnd
Low Pass
Filter
Vda
Tout
Vref
Aout X
Aout Y
MXA2312A FUNCTIONAL BLOCK DIAGRAM
signals below 2 milli-g to be resolved at 1 Hz bandwidth.
The 3dB rolloff of the device occurs at 30 Hz but is
expandable to >160 Hz (refernce Application Note AN-
00MX-003). The MXA2312A is available in a low profile
LCC surface mount package (5mm x 5mm x 2mm height).
It is hermetically sealed and are operational over a -40°C to
+105°C temperature range.
Due to the standard CMOS structure of the MXA2312A,
additional circuitry can easily be incorporated into custom
versions for high volume applications. Contact the factory
for more information.
MEMSIC, Inc.
100 Burtt Road, Andover, MA 01810
Tel: 978.623.8188
Fax: 978.623.9945
www.memsic.com
www.DataSheet.in
1 page  
or software. Any compensation for this effect could be
done instinctively by the game player.
For applications where sensitivity changes of a few percent
are acceptable, the above equation can be approximated
with a linear function. Using a linear approximation, an
external circuit that provides a gain adjustment of –0.9%/°C
would keep the sensitivity within 10% of its room
temperature value over a 0°C to +50°C range.
For applications that demand high performance, a low cost
micro-controller can be used to implement the above
equation. A reference design using a Microchip MCU (p/n
16F873/04-SO) and MEMSIC developed firmware is
available by contacting the factory. With this reference
design, the sensitivity variation over the full temperature
range (-40°C to +105°C) can be kept below 3%. Please
visit the MEMSIC web site at www.memsic.com for
reference design information on circuits and programs
including look up tables for easily incorporating sensitivity
compensation.
DISCUSSION OF TILT APPLICATIONS AND
RESOLUTION
Tilt Applications: One of the most popular applications of
the MEMSIC accelerometer product line is in
tilt/inclination measurement. An accelerometer uses the
force of gravity as an input to determine the inclination
angle of an object.
A MEMSIC accelerometer is most sensitive to changes in
position, or tilt, when the accelerometer’s sensitive axis is
perpendicular to the force of gravity, or parallel to the
Earth’s surface. Similarly, when the accelerometer’s axis is
parallel to the force of gravity (perpendicular to the Earth’s
surface), it is least sensitive to changes in tilt.
Table 1 and Figure 2 help illustrate the output changes in
the X- and Y-axes as the unit is tilted from +90° to 0°.
Notice that when one axis has a small change in output per
degree of tilt (in mg), the second axis has a large change in
output per degree of tilt. The complementary nature of
these two signals permits low cost accurate tilt sensing to
be achieved with the MEMSIC device (reference
application note AN-00MX-007).
X
+900
00
gravity
Y
Top View
Figure 2: Accelerometer Position Relative to Gravity
X-Axis
Y-Axis
X-Axis
Orientation
Change
Change
To Earth’s X Output per deg. Y Output per deg.
Surface
(g) of tilt (g) of tilt
(deg.)
(mg) (mg)
90
1.000
0.15 0.000 17.45
85
0.996
1.37 0.087 17.37
80
0.985
2.88 0.174 17.16
70
0.940
5.86 0.342 16.35
60
0.866
8.59 0.500 15.04
45
0.707
12.23
0.707
12.23
30
0.500
15.04
0.866
8.59
20
0.342
16.35
0.940
5.86
10
0.174
17.16
0.985
2.88
5
0.087
17.37
0.996
1.37
0
0.000
17.45
1.000
0.15
Table 1: Changes in Tilt for X- and Y-Axes
Minimum Resolution: The accelerometer resolution is
limited by noise. The output noise will vary with the
measurement bandwidth. With the reduction of the
bandwidth, by applying an external low pass filter, the
output noise drops. Reduction of bandwidth will improve
the signal to noise ratio and the resolution. The output noise
scales directly with the square root of the measurement
bandwidth. The maximum amplitude of the noise, its peak-
to- peak value, approximately defines the worst case
resolution of the measurement. The peak-to-peak noise is
approximately equal to 6.6 times the rms value (with an
average uncertainty of .1%). The maximum noise for 1.0Hz
bandwidth will be1mg Hz . For example, if the
bandwidth is increased to 10 Hz, then 3.162 mg is the
maximum rms noise and 20.87mg is the maximum peak -
to-peak noise.
EXTERNAL FILTERS
AC Coupling: For applications where only dynamic
accelerations (vibration) are to be measured, it is
recommended to ac couple the accelerometer output as
shown in Figure 3. The advantage of ac coupling is that
variations from part to part of zero g offset and zero g
offset versus temperature can be eliminated. Figure 3 is a
HPF (high pass filter) with a –3dB breakpoint given by the
equation: f = 12πRC . In many applications it may be
desirable to have the HPF –3dB point at a very low
frequency in order to detect very low frequency
accelerations. Sometimes the implementation of this HPF
may result in unreasonably large capacitors, and the
designer must turn to digital implementations of HPFs
where very low frequency –3dB breakpoints can be
achieved.
MEMSIC MXA2312A Rev .E
www.DataSheet.in
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5/15/2004
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