MXC62320MB datasheet(5/8 Pages) MEMSIC

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MEMSIC MXC6232xG/H/M/N Rev.A

Page 5 of 8

4/11/2010

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 it is a gas in the MEMSIC sensor.

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.

MXC6232xG/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

Y-Axis

X-Axis

Orientation

To Earth’s

Surface

(deg.)

X Output

(g)

Change

per deg.

of tilt

(mg)

Y Output

(g)

Change

per deg.

of tilt

(mg)

1.000

0.15

0.000

17.45

0.996

1.37

0.087

17.37

0.985

2.88

0.174

17.16

0.940

5.86

0.342

16.35

0.866

8.59

0.500

15.04

0.707

12.23