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MXC6202 Datasheet PDF : 10 Pages
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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
except that the 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.
MXC6202G/H/M/N PIN DESCRIPTIONS
VDD – This is the supply input for the circuits and the
sensor heater in the accelerometer. The DC voltage should
be between 2.7 and 3.6 volts. 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.
COM– This pin should be connected to ground.
TEST– Do Not Connect, factory use only.
VDD2– This pin is the I2C input digital power supply, the
voltage on this pin determines the I2C bus logic voltage,
and is 1.8V compatible. Note: The voltage on this pin
should never go higher than the voltage on VDD, if VDD2
has a lower power supply voltage than VDD, power should
be applied to VDD first.
SDA– This pin is the I2C serial data line, and operates in
FAST (400 KHz.) mode.
SCL– This pin is the I2C serial clock line, and operates in
FAST (400 KHz.) mode.
DISCUSSION OF TILT APPLICATIONS AND
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.
Following table and figure 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).
Accelerometer Position Relative to Gravity
X-Axis
Orientatio
n
To Earth’s
Surface
(deg.)
90
85
80
70
60
45
30
20
10
5
0
X-Axis
Y-Axis
X Output
(g)
Change
per deg.
of tilt
(mg)
Y Output
(g)
Change
per deg.
of tilt
(mg)
1.000
0.15
0.000
0.996
1.37
0.087
0.985
2.88
0.174
0.940
5.86
0.342
0.866
8.59
0.500
0.707
12.23
0.707
0.500
15.04
0.866
0.342
16.35
0.940
0.174
17.16
0.985
0.087
17.37
0.996
0.000
17.45
1.000
Changes in Tilt for X- and Y-Axes
17.45
17.37
17.16
16.35
15.04
12.23
8.59
5.86
2.88
1.37
0.15
MEMSIC MXC6202G/H/M/N Rev.B
Page 7 of 10
11/10/2005
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