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PDF MXD7210HL Data sheet ( Hoja de datos )
| Número de pieza | MXD7210HL | |
| Descripción | Low Noise -10 g Dual Axis Accelerometer | |
| Fabricantes | MEMSIC | |
| Logotipo |  |
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Low Cost, Low Noise ±10 g Dualwww.DataSheet4U.com
Axis Accelerometer with Digital
Outputs
MXD7210GL/HL/ML/NL
FEATURES
Low cost
Resolution better than 1milli-g at 1Hz
Dual axis accelerometer fabricated on a monolithic
CMOS IC
On chip mixed signal processing
No moving parts; No loose particle issues
>50,000 g shock survival rating
5mm X 5mm X 2mm LCC package
2.7V to 5.25V single supply continuous operation
Compensated for Sensitivity over temperature
Ultra low initial Zero-g Offset
No adjustment needed outside
APPLICATIONS
Computer Peripherals
Information Appliances
Alarms and Motion Detectors
Disk Drives
Vehicle Security
MXD7210GL/HL/ML/NL FUNCTIONAL BLOCK DIAGRAM
GENERAL DESCRIPTION
The MXD7210GL/HL/ML/NL is a low cost, dual axis
accelerometer fabricated on a standard, submicron CMOS
process. It is a complete sensing system with on-chip mixed
signal processing. The MXD7210GL/HL/ML/NL measures
acceleration with a full-scale range of ±10 g and a sensitivity
of 4%/g @5V. It can measure both dynamic acceleration
(e.g. vibration) and static acceleration (e.g. gravity). The
MXD7210GL/HL/ML/NL 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 greater than
50,000 g, leading to significantly lower failure rate and lower
loss due to handling during assembly and at customer field
application.
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.
The MXD7210GL/HL/ML/NL provides two digital outputs
that are set to 50% duty cycle at zero g acceleration. The
outputs are digital with duty cycles (ratio of pulse width to
period) that are proportional to acceleration. The duty cycle
outputs can be directly interfaced to a microprocessor.
The typical noise floor is 0.4 mg/ Hz allowing signals
below 1milli-g to be resolved at 1 Hz bandwidth. The
MXR7210GL/HL/ML/NL is packaged in a hermetically
sealed LCC surface mount package (5 mm x 5 mm x 2 mm
height) and is operational over a 0°C to 70°C(GL/HL) or a -
40°C to +85°C(ML/NL) temperature range.
MEMSIC, Inc.
800 Turnpike St., Suite 202, North Andover, MA 01845
Tel: 978.738.0900
Fax: 978.738.0196
www.memsic.com
MEMSIC MXD7210GL/HL/ML/NL
Page 1 of 10
2003.08.04
1 page  
DIGITAL INTERFACE
The MXD7210GL/HL/ML/NL 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 MXD7210GL/HL/ML/NL 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 4% 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)/0.04
0g = 50% Duty Cycle
T2= 2.5ms or 10ms (factory programmable)
Figure 3: Typical output Duty C ycle
CHOOSING T2 AND COUNTEwRwwF.RDEatQaSUhEeeNtC4UY.com
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.
T2 (ms)
2.5
2.5
2.5
10.0
10.0
10.0
MEMSIC
Sample
Rate
400
400
400
100
100
100
Counter-
Clock
Rate
(MHz)
2.0
1.0
0.5
2.0
1.0
0.5
Counts
Per T2
Cycle
5000
2500
1250
20000
10000
5000
Counts
per g
200
100
50
800
400
200
Reso-
lution
(mg)
5.0
10
20
1.25
2.5
5.0
Table 2: Trade-Offs Between Microcontroller Counter Rate and
T2 Period.
CONVERTING THE DIGITAL OUTPUT TO AN
ANALOG OUTPUT
The PWM output can be easily converted into an analog
output by integration. A simple RC filter can do the
conversion. Note that that the impedance of the circuit
following the integrator must be much higher than the
impedance of the RC filter. Reference figure 4 for an
example.
DOUT
MEMSIC
Accel.
10K
1uF
AOUT
Figure 4: Converting the digital output to an analog
voltage
MEMSIC MXD7210GL/HL/ML/NL
Page 5 of 10
2003.08.04
5 Page | ||
| Páginas | Total 10 Páginas | |
| PDF Descargar | [ Datasheet MXD7210HL.PDF ] | |
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