MXD2020N Datasheet PDF - Memsic
| Part Number | MXD2020N | |
| Description | Dual Axis Accelerometer | |
| Manufacturers | Memsic | |
| Logo |  |
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Improved, Ultra Low Noise
±1.7 g Dual Axis Accelerometer
with Digital Outputs
MXD2020G/H
MXD2020M/N
FEATURES
Resolution better than 1 mg
Dual axis accelerometer fabricated on a monolithic CMOS IC
RoHS compliant
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)
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/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 MXD2020G/H/M/N 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 MXD2020G/H/M/N
measures acceleration with a full-scale range of ±1.7 g and
a sensitivity of 20%/g @5V at 25°C. It can measure both
dynamic acceleration (e.g. vibration) and static acceleration
(e.g. gravity).
The MXD2020G/H/M/N 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
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
DOUTX
DOUTY
MXD2020G/H/M/N FUNCTIONAL BLOCK DIAGRAM
The MXD2020G/H/M/N 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 mg to be resolved at 1 Hz bandwidth. The
MXD2020G/H/M/N 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/N) and 0°C to
70°C(G/H) 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, MA01845, USA
Tel: +1 978 738 0900
Fax: +1 978 738 0196
www.memsic.com
MEMSIC MXD2020G/H/M/N Rev.G
Page 1 of 7
2/26/2007
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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 MXD2020G/H/M/N 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 MXD2020G/H/M/N 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).
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 2: 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.
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 3 for an
example.
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.
DOUT
10K
MEMSIC
Accel.
1uF
AOUT
Figure 3: Converting the digital output to an analog voltage
MEMSIC MXD2020G/M/N/H Rev.G
Page 5 of 7
2/26/2007
Preview 5 Page |
Part DetailsOn this page, you can learn information such as the schematic, equivalent, pinout, replacement, circuit, and manual for MXD2020N electronic component. |
| Information | Total 7 Pages | |
| Link URL | [ Copy URL to Clipboard ] | |
| Download | [ MXD2020N.PDF Datasheet ] | |
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