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PDF MXD2020GL Data sheet ( Hoja de datos )
| Número de pieza | MXD2020GL | |
| Descripción | Dual Axis Accelerometer | |
| Fabricantes | Memsic | |
| Logotipo |  |
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Improved, Ultra Low Noise ±1 g
Dual Axis Accelerometer with
Digital Outputs
MXD2020GL/HL
MXD2020ML/NL
FEATURES
Resolution better than 1 milli-g
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
3.0V to 5.25V single supply continuous operation
Continuous self test
Independent axis programmability (special order)
Compensated for Sensitivity over temperature
Ultra low initial Zero-g Offset
APPLICATIONS
Automotive – Vehicle Security/Vehicle stability control/
Headlight Angle Control/Tilt Sensing
Security – Gas Line/Elevator/Fatigue Sensing
Information Appliances – Computer Peripherals/PDA’s/Mouse
Smart Pens/Cell Phones
Gaming – Joystick/RF Interface/Menu Selection/Tilt Sensing
GPS – electronic Compass tilt Correction
Consumer – LCD projectors, pedometers, blood pressure
Monitor, digital cameras
GENERAL DESCRIPTION
The MXD2020GL/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 mode signal processing. The
MXD2020GL/HL/ML/NL measures acceleration with a
full-scale range of ±1 g and a sensitivity of 20%/g. It can
measure both dynamic acceleration (e.g. vibration) and
static acceleration (e.g. gravity).
The MXD2020GL/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 of 50,000
g, leading to significantly lower failure rate and lower loss
due to handling during assembly.
Sck
(optional)
Internal
O s c illa to r
CLK
Heater
Control
Continous
Self Test
T e m p e ra 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
MXD2020GL/HL/ML/NL FUNCTIONAL BLOCK
DIAGRAM
The MXD2020GL/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 micro-
processor.
The typical noise floor is 0.2 mg/ Hz allowing signals
below 1 milli-g to be resolved at 1 Hz bandwidth. The
MXD2020GL/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 -40°C to 105°C(M/NL) and
0°C to 70°C(G/HL) temperature range.
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 St., Suite 202, North Andover, MA 01845
Tel: 978.738.0900
Fax: 978.738.0196
www.memsic.com
MEMSIC MXD2020GL/ML
Page 1 of 7
2002.08.29.1
1 page  
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%).
DIGITAL INTERFACE
The MXD2020GL/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 MXD2020GL/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 20% 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
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.
Pulse width
Time period of the “on” pulse. Defined as
T1.
T2
T1
A (g)= (T1/T2 - 0.5)/20%
0g = 50% Duty Cycle
T2= 2.5ms or 10ms (factory programmable)
Figure 3: 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.
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
1000
500
250
4000
2000
1000
Reso-
lution
(mg)
1.0
2.0
4.0
0.25
0.5
1.0
Table 2: Trade-Offs Between Microcontroller Counter Rate and
T2 Period.
USING THE ACCELEROMETER IN VERY LOW
POWER APPLICATIONS (BATTERY OPERATION)
In applications with power limitations, power cycling can
be used to extend the battery operating life. One important
consideration when power cycling is that the accelerometer
turn on time limits the frequency bandwidth of the
accelerations to be measured. For example, operating at
3.0V the turn on time is 40mS. To double the operating
time, a particular application may cycle power ON for
40mS, then OFF for 40mS, resulting in a measurement
period of 80mS, or a frequency of 12.5Hz. With a
frequency of measurements of 12.5Hz, accelerations
changes as high as 6.25Hz can be detected. Power cycling
can be used effectively in many inclinometry applications,
where inclination changes can be slow and infrequent.
MEMSIC MXD2020GL/ML/NL/HL
Page 5 of 7
2002.08.29.1
5 Page | ||
| Páginas | Total 7 Páginas | |
| PDF Descargar | [ Datasheet MXD2020GL.PDF ] | |
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