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PDF MXA2500E Data sheet ( Hoja de datos )
| Número de pieza | MXA2500E | |
| Descripción | Offset Drift 1 g Dual Axis Accelerometer | |
| Fabricantes | Memsic | |
| Logotipo |  |
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Ultra Low Noise, Offset Drift ±1 g Dual Axis
Accelerometer with Analog Outputs
FEATURES
Better than 1 milli-g resolution
Dual axis accelerometer fabricated on a monolithic
CMOS IC
On-chip mixed mode signal processing
No moving parts
50,000 g shock survival rating
17 Hz bandwidth expandable to >160 Hz
3V to 5.25V single supply continuous operation
Small (5mm x 5mm x 2mm) surface mount package
Continuous self test
Custom programmable specifications
Independent axis programmability (special order)
APPLICATIONS
Automotive – Vehicle Security/Active Suspension/ABS
Headlight 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 MXA2500E is an ultra low noise and low cost, dual
axis accelerometer fabricated on a standard, submicron
CMOS process. It is a complete sensing system with on-
chip mixed mode signal processing. The MXA2500E
measures acceleration with a full-scale range of ±1 g and a
sensitivity of 500mV/g at 25°C. (The MEMSIC
accelerometer product line extends from ±0.5g to ±250g
with custom versions available above ±10 g.) It can
measure both dynamic acceleration (e.g., vibration) and
static acceleration (e.g., gravity). The MXA2500E 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 of 50,000 g, leading to significantly lower failure
rates and lower loss due to handling during assembly.
MXA2500E
Sck
(optional)
Internal
Oscillator
Temperature
Sensor
Voltage
CLK 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
AOUTX
AOUTY
MXA2500E FUNCTIONAL BLOCK DIAGRAM
The MXA2500E provides an absolute analog output The
typical noise floor is 0.2 mg/ Hz allowing signals below
1 milli-g to be resolved at 1 Hz bandwidth. The 3dB
rolloff of the device occurs at 17 Hz but is expandable to
>160 Hz (ref. Application Note AN-00MX-003). The
MXA2500E is available in a low profile LCC surface
mount package (5 mm x 5 mm x 2 mm). It is hermetically
sealed and is operational over a -40°C to +105°C
temperature range. It also contains an on-chip temperature
sensor and a bandgap voltage reference.
Due to the standard CMOS structure of the MXA2500E,
additional circuitry can easily be incorporated into custom
versions for high volume applications. Contact the factory
for more information.
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.
MEMSIC, Inc.
800 Turnpike Street, Suite 202 , North Andover, MA 01845
Tel: 978.738.0900
Fax: 978.738.0196
www.memsic.com
MEMSIC MXA2500E Rev C
www.DataSheet.in
Page 1 of 9
29/7/2003
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
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. With a simple RC low pass filter, the rms
noise is calculated as follows:
Noise (mg rms) = Noise(mg/ Hz ) * (Bandwidth(Hz) *1.6)
The peak-to-peak noise is approximately equal to 6.6 times
the rms value (for an average uncertainty of 0.1%).
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 MXA2500E Rev C
www.DataSheet.in
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29/7/2003
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| PDF Descargar | [ Datasheet MXA2500E.PDF ] | |
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