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PDF MXD2002A Data sheet ( Hoja de datos )
| Número de pieza | MXD2002A | |
| Descripción | (MXD2002A/B) Dual Axis Accelerometer | |
| Fabricantes | Memsic | |
| Logotipo |  |
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Low Cost, ±10 g Dual Axis
Accelerometer with Digital Outputs
FEATURES
Dual axis accelerometer fabricated on a monolithic CMOS IC
On-chip mixed mode signal processing
Resolution better than 6 milli-g
50,000 g shock survival rating
30 Hz bandwidth
2.70V to 5.25V single supply operation
Small (5mm x 5mm x 2mm) surface mount package
Continuous self test
Independently programmable axis (factory special)
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
The MXD2002A/B is a very low cost, dual axis
accelerometer fabricated on a standard, submicron CMOS
process. The MXD2002A/B measures acceleration with a
full-scale range of ±10 g. (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 MXD2002A/B 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 MXD2002A/B provides a digital output (ref. other
MEMSIC data sheets for analog or ratiometric analog
outputs). The outputs are digital signals with duty cycles
(ratio of pulsewidth to period) that are proportional to
acceleration. The duty cycle outputs can be directly
interfaced to a micro-processor.
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.
MXD2002A/B
Sck
(optional)
Internal
O s c illa to r
CLK
Heater
Control
Continous
Self Test
T e m p era tu re
Sensor
Voltage
Reference
X axis
LPF
A/D
Factory Adjust
Offset & Gain
2-AXIS
SENSOR
Y axis
Vdd
Gnd
LPF
A/D
Vda
Tout
Vref
Dout X
Dout Y
MXD2002A/B FUNCTIONAL BLOCK DIAGRAM
The typical noise floor is .0015% duty cycle
/ Hz allowing
signals below 6 milli-g to be resolved at 1 Hz bandwidth.
The MXD2002A/B is available in a low profile LCC
surface mount package (5mm x 5mm x 2mm height). It is
hermetically sealed and operational over a -40°C to +105°C
temperature range.
Due to the standard CMOS structure of the MXD2002A/B,
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
MEMSIC MXD2002A/B Rev.E
Page 1 of 8
5/15/2004
1 page  
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: Accelerometers can be used in a
wide variety of low g applications such as tilt and
orientation. The device noise floor will vary with the
measurement bandwidth. With the reduction of the
bandwidth the noise floor drops. This will improve the
signal to noise ratio of the measurement and 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 as the rms
value (with an average uncertainty of .1%). The maximum
noise for 1.0Hz bandwidth will be 1 mg/ Hz . If the
bandwidth is increased to 10 Hz for example: 3.162 mg is
the maximum rms noise and 20.87mg is the maximum
peak -to-peak noise.
DIGITAL INTERFACE
The MXD2002A/B is easily interfaced with low cost
microcontrollers. For the digital output accelerometer, one
digital input port is required to read one accelerometer
output. For the analog output accelerometer, many low cost
microcontrollers are available today that feature integrated
a/d (analog to digital converters) with resolutions ranging
from 8 to 12 bits.
In many applications the microcontroller provides an
effective approach for the temperature compensation of the
sensitivity and the zero g offset. Specific code set, reference
designs, and applications notes are available from the
factory. The following parameters must be considered in a
digital interface:
Resolution: smallest detectable change in input acceleration
Bandwidth: detectable accelerations in a given period of
time
Acquisition Time: the duration of the measurement of the
acceleration signal
DUTY CYCLE DEFINITION
The MXD2002A/B has two PWM duty cycle outputs (x,y).
The acceleration is proportional to the ratio T1/T2. The
zero g output is set to 50% duty cycle and the sensitivity
scale factor is set to 2% duty cycle change per g. These
nominal values are affected by the initial tolerance of the
device including zero g offset error and sensitivity error.
This device is offered from the factory programmed to
either a 10ms period (100 Hz) or a 2.5ms period (400Hz).
T1
T2 (Period)
Duty Cycle
Pulse width
Length of the “on” portion of the cycle.
Length of the total cycle.
Ratio of the “0n” time (T1) of the cycle to
the total cycle (T2). Defined as T1/T2.
Time period of the “on” pulse. Defined as
T1.
T2
T1
A (g)= (T1/T2 - 0.5)/2%
0g = 50% Duty Cycle
T2= 2.5ms or 10ms (factory programmable)
Figure 4: Typical output Duty C ycle
CHOOSING T2 AND COUNTER FREQUENCY
DESIGN TRADE-OFFS
The noise level is one determinant of accelerometer
resolution. The second relates to the measurement
resolution of the counter when decoding the duty cycle
output. The actual resolution of the acceleration signal is
limited by the time resolution of the counting devices used
to decode the duty cycle. The faster the counter clock, the
higher the resolution of the duty cycle and the shorter the
T2 period can be for a given resolution. Table 2 shows
some of the trade-offs. It is important to note that this is the
resolution due to the microprocessors’ counter. It is
probable that the accelerometer’s noise floor may set the
lower limit on the resolution.
Counter-
MEMSIC Clock Counts
Reso-
Sample
Rate Per T2 Counts lution
T2 (ms)
Rate
(MHz) Cycle per g (mg)
2.5 400
2.0
5000
100
10
2.5 400
1.0 2500 50 20
2.5 400
0.5 1250 25 40
10.0 100
2.0
20000
400
2.5
10.0 100
1.0
10000
200
5.0
10.0 100
0.5
5000
100
10
Table 2: Trade-Offs Between Microcontroller Counter Rate and
T2 Period.
MEMSIC MXD2002A/B Rev.E
Page 5 of 8
5/15/2004
5 Page | ||
| Páginas | Total 8 Páginas | |
| PDF Descargar | [ Datasheet MXD2002A.PDF ] | |
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