Low Cost,
10 g Dual Axis
Accelerometer with Ratiometric Outputs
MXR2050A
FEATURES
Dual axis accelerometer fabricated on a monolithic CMOS IC
On-chip mixed mode signal processing
Resolution better than 2 milli-g
50,000 g shock survival rating
30 Hz bandwidth expandable to >160 Hz
2.70V to 5.25V single supply operation
Low height (2.0mm) surface mount package
Continuous self test
Independent axis programmability (special order)
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
Internal
Oscillator
Sck
(optional)
CLK
Heater
Control
X axis
Y axis
Factory Adjust
Offset & Gain
Low Pass
Filter
Low Pass
Filter
Temperature
Sensor
Voltage
Reference
Vref
Aout X
Vdd
Vda
Gnd
2-AXIS
SENSOR
Aout Y
Tout
Continous
Self Test
MXR2050A FUNCTIONAL BLOCK DIAGRAM
GENERAL DESCRIPTION
The MXR2050A is a low cost, dual axis accelerometer
fabricated on a standard, submicron CMOS process. The
MXR2050A measures acceleration with a full-scale range
of
10 g and a sensitivity of 50mV/g at 25C. (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 MXR2050A 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 MXR2050A provides a ratiometric analog output that
is proportional to 50% of the supply voltage at zero g
acceleration. (ref. other MEMSIC data sheets for absolute
analog or digital outputs). The typical noise floor is
0.75 mg/ Hz allowing signals below 2 milli-g to be
resolved at 1 Hz bandwidth. The 3dB rolloff of the device
occurs at 30 Hz but is expandable to >160 Hz (reference
Application note AN-00MX-003). The MXR2050A is
available in a low profile LCC surface mount package
(5mm X 5mm X 2mm). It is hermetically sealed and
operational over a -40
C to +105C temperature range.
Due to the standard CMOS structure of the MXR2050A,
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.
100 Burtt Road, Andover, MA 01810
Tel: 978.623.8188
Fax: 978.623.9945
www.memsic.com
MEMSIC MXR2050A Rev 01 Page 2 of 8 04/02
MXR2050A SPECIFICATIONS
(Measurements @ 25
C, Acceleration = 0 g unless otherwise noted; V
DD
, V
DA
= 5.0V
unless otherwise specified)
Parameter
Conditions
Min
MXR2050A
Typ
Max
Units
SENSOR INPUT
Measurement Range
1
Each Axis
10.0
g
Nonlinearity
Best fit straight line
1.0
2.0
% of FS
Alignment Error
2
1.0
degrees
Transverse Sensitivity
3
2.0
%
SENSITIVITY
Sensitivity, Analog Outputs at pins
A
OUTX
and A
OUTY
6
Each Axis
@5.0V supply
45
50
55
mV/g
Change over Temperature (uncompensated)
4
from 25C, at 40C
+93
%
from 25C, at +105C
-47 %
Change over Temperature (compensated)
4
from 25C, 40C to +105C
<3.0 %
ZERO g BIAS LEVEL
0 g Offset
6
Each Axis
-0.6
0.00
+0.6
g
0 g Voltage
6
2.47 2.5 2.53 V
0 g Offset over Temperature
from 25C
from 25C, based on 50mV/g
2.0
0.10
mg/
C
mV/
C
NOISE PERFORMANCE
Noise Density, rms)
7
Without frequency compensation
0.75
1
mg/
Hz
FREQUENCY RESPONSE
3dB Bandwidth - uncompensated
30
Hz
3dB Bandwidth - compensated
5
>160
Hz
TEMPERATURE OUTPUT
T
out
Voltage
1.21
1.25
1.29
V
Sensitivity
4.6
5.0
5.4
mV/
K
VOLTAGE REFERENCE
V
Ref
@2.7V-5.0V
supply
2.4
2.5
2.65
V
Change over Temperature
0.1
mV/
C
Current Drive Capability
Source
100
A
SELF TEST
Continuous Voltage at A
OUTX
, A
OUTY
under
Failure
@5.0V Supply, output rails to
supply voltage
5.0
V
Continuous Voltage at A
OUTX
, A
OUTY
under
Failure
@2.7V Supply, output rails to
supply voltage
2.7
V
A
OUTX
and A
OUTY
OUTPUTS
Normal Output Range
@5.0V Supply
@2.7V Supply
0.1
0.1
4.9
2.6
V
V
Current
Source or sink, @ 2.7V-5.0V supply
100
A
Turn-On Time
@5.0V Supply
@2.7V Supply
100
40
mS
mS
POWER SUPPLY
Operating Voltage Range
2.7
5.25
V
Supply Current
@ 5.0V
2.5
4.3
5
mA
Supply Current)
8
@
2.7V
3.0
5.8
6.7
mA
TEMPERATURE RANGE
Operating Range
-40
+105
C
NOTES
1
Guaranteed by measurement of initial offset and sensitivity.
2
Alignment error is specified as the angle between the true and indicated
axis of sensitivity.
3
Transverse sensitivity is the algebraic sum of the alignment and the
inherent sensitivity errors.
4
The sensitivity change over temperature for thermal accelerometers is
based on variations in heat transfer that are governed by the laws of
physics and it is highly consistent from device to device. Please refer to
the section in this data sheet titled "Compensation for the Change of
Sensitivity over Temperature" for more information.
5
External circuitry is required to extend the 3dB bandwidth.
6
The device operates over a 2.7V to 5.0V supply range. The output zero g
reference voltage scales 50% of the supply voltage. Sensitivity has a linear
scale over the supply range of 2.7 to 5.25 volts according to the ratio
(Vdd/5.0 volts) x ( 50mV/g).
7
The
ratiometric device will require a low pass filter. These devices have
a 25Khz signal that couples directly to the output. It is recommended to
filter with a minimum of 200Hz low pass filter.
8
Note that the accelerometer has a constant heater power control circuit
thereby requiring higher supply current at lower operating voltage.
MEMSIC MXR2050A Rev 01 Page 3 of 8 04/02
ABSOLUTE MAXIMUM RATINGS*
Supply Voltage (V
DD
, V
DA
) .....................-0.5 to +7.0V
Storage Temperature ......................-65
C to +150C
Acceleration ............................................50,000 g
*Stresses above those listed under Absolute Maximum Ratings may cause permanent
damage to the device. This is a stress rating only; the functional operation of the
device at these or any other conditions above those indicated in the operational
sections of this specification is not implied. Exposure to absolute maximum rating
conditions for extended periods may affect device reliability.
Package Characteristics
Package
JA
JC
Device Weight
LCC-8
110
C/W 22C/W
< 1 gram
Ordering Guide
Model Package
Style
R2050AL LCC-8
SMD*
*LCC parts are shipped in tape and reel packaging.
Caution
ESD (electrostatic discharge) sensitive device.
8
4
1
2
3
7
6
5
Top View
ME
MS
I
C
X +g
Y +g
Note: The MEMSIC logo's arrow indicates the +X sensing
direction of the device. The +Y sensing direction is rotated 90
away from the +X direction.
Pin Description: LCC-8 Package
Pin Name Description
1 T
OUT
Temperature (Analog Voltage)
2 A
OUTY
Y-Axis Acceleration Signal
3 Gnd Ground
4 V
DA
Analog Supply Voltage
5 A
OUTX
X-Axis Acceleration Signal
6 V
ref
2.5V
Reference
7
Sck
Optional External Clock
8 V
DD
Digital Supply Voltage
MEMSIC MXR2050A Rev 01 Page 4 of 8 04/02
THEORY OF OPERATION
The MEMSIC device is a complete dual-axis acceleration
measurement system fabricated on a monolithic CMOS IC
process. The device operation is based on heat transfer by
natural convection and operates like other accelerometers
having a proof mass. The stationary element, or `proof
mass', in the MEMSIC sensor is a gas.
A single heat source, centered in the silicon chip is
suspended across a cavity. Equally spaced
aluminum/polysilicon thermopiles (groups of
thermocouples) are located equidistantly on all four sides of
the heat source (dual axis). Under zero acceleration, a
temperature gradient is symmetrical about the heat source,
so that the temperature is the same at all four thermopiles,
causing them to output the same voltage.
Acceleration in any direction will disturb the temperature
profile, due to free convection heat transfer, causing it to be
asymmetrical. The temperature, and hence voltage output
of the four thermopiles will then be different. The
differential voltage at the thermopile outputs is directly
proportional to the acceleration. There are two identical
acceleration signal paths on the accelerometer, one to
measure acceleration in the x-axis and one to measure
acceleration in the y-axis. Please visit the MEMSIC
website at www.memsic.com for a picture/graphic
description of the free convection heat transfer principle.
PIN DESCRIPTIONS
V
DD
This is the supply input for the digital circuits and
the sensor heater in the accelerometer. The DC voltage
should be between 2.70 and 5.25 volts. Refer to the section
on PCB layout and fabrication suggestions for guidance on
external parts and connections recommended.
V
DA
This is the power supply input for the analog
amplifiers in the accelerometer. Refer to the section on
PCB layout and fabrication suggestions for guidance on
external parts and connections recommended.
Gnd This is the ground pin for the accelerometer.
A
OUTX
This pin is the output of the x-axis acceleration
sensor. The user should ensure the load impedance is
sufficiently high as to not source/sink >100
A. While the
sensitivity of this axis has been programmed at the factory
to be the same as the sensitivity for the y-axis, the
accelerometer can be programmed for non-equal
sensitivities on the x- and y-axes. Contact the factory for
additional information on this feature.
A
OUTY
This pin is the output of the y-axis acceleration
sensor. The user should ensure the load impedance is
sufficiently high as to not source/sink >100
A. While the
sensitivity of this axis has been programmed at the factory
to be the same as the sensitivity for the x-axis, the
accelerometer can be programmed for non-equal
sensitivities on the x- and y-axes. Contact the factory for
additional information on this feature.
T
OUT
This pin is the buffered output of the temperature
sensor. The analog voltage at T
OUT
is an indication of the
die temperature. This voltage is useful as a differential
measurement of temperature from ambient and not as an
absolute measurement of temperature. After correlating the
voltage at T
OUT
to 25
C ambient, the change in this voltage
due to changes in the ambient temperature can be used to
compensate for the change over temperature of the
accelerometer offset and sensitivity. Please refer to the
section on Compensation for the Change in Sensitivity
Over Temperature for more information.
Sck The standard product is delivered with an internal
clock option (800kHz). This pin should be grounded
when operating with the internal clock. An external
clock option can be special ordered from the factory
allowing the user to input a clock signal between 400kHz
and 1.6MHz.
V
ref
A reference voltage is available from this pin. It is
set at 2.50V typical and has 100
A of drive capability.
COMPENSATION FOR THE CHANGE IN
SENSITIVITY OVER TEMPERATURE
All thermal accelerometers display the same sensitivity
change with temperature. The sensitivity change depends
on variations in heat transfer that are governed by the laws
of physics. Manufacturing variations do not influence the
sensitivity change, so there are no unit to unit differences in
sensitivity change. The sensitivity change is governed by
the following equation (and shown in Figure 1 in
C):
S
i
x T
i
2.67
= S
f
x T
f
2.67
where S
i
is the sensitivity at any initial temperature T
i
, and
S
f
is the sensitivity at any other final temperature T
f
with
the temperature values in
K.
0.0
0.5
1.0
1.5
2.0
-40
-20
0
20
40
60
80
100
Temperature (C)
Sensitivity (normalized)
Figure 1: Thermal Accelerometer Sensitivity
In gaming applications where the game or controller is
typically used in a constant temperature environment,
sensitivity might not need to be compensated in hardware
MEMSIC MXR2050A Rev 01 Page 5 of 8 04/02
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 +50C 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 +105C) 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
MINIMUM 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).
Top View
X
Y
+90
0
0
0
gravity
ME
M
S
I
C
Figure 2: Accelerometer Position Relative to Gravity
X-Axis
Y-Axis
X-Axis
Orientatio
n
To Earth's
Surface
(deg.)
X Output
(g)
Change
per deg.
of tilt
(mg)
Y Output
(g)
Change
per deg.
of tilt
(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: 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. The peak-to-peak noise is
approximately equal to 6.6 times the rms value (with an
average uncertainty of .1%). The maximum noise for 1.0Hz
bandwidth will be
Hz
mg
1
. For example, if the
bandwidth is increased to 10 Hz, then 3.162 mg is the
maximum rms noise and 20.87mg is the maximum peak -
to-peak noise.
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:
RC
f
2
1
=
. 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.
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