mxr7305vf memsic, mxr7305vf Datasheet - Page 4

• Manufacturer Part Number: mxr7305vf
• Description: Improved Low Cost ?5 G Dual-axis Accelerometer With Ratiometric Analog Outputs
• Manufacturer: memsic

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 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 MXR7305V, one to
measure acceleration in the x-axis and one to measure
acceleration in the Y-axis. For more details visit the
MEMSIC website at www.memsic.com for a
picture/graphic description of the free convection heat
transfer principle.
PIN DESCRIPTIONS
V
circuits.
For proper operation V
volts. Refer to the section on PCB layout and fabrication
suggestions for guidance on external parts and connections
recommended.
X
It is capable of sinking or sourcing up to 100μA. The user
should ensure the load impedance is sufficiently high as to
not source/sink >100μA. While the sensitivity of this axis
has been programmed at the factory to be the same as the
sensitivity for the Y-axis, the MXR7305V can be
programmed for non-equal sensitivities on the x- and y-
axes.
Contact Memsic’s local office for additional information.
MEMSIC MXR7305VF Rev.A
DD
OUT
– (pin 8). Supply voltage input for digital and analog
– (pin 7). X-axis acceleration signal output
DD
must be between 4.50 and 5.25
Page 4 of 6
Y
It is capable of sinking or sourcing up to 100μA. The user
should ensure the load impedance is sufficiently high as to
not source/sink >100μA. While the sensitivity of this axis
has been programmed at the factory to be the same as the
sensitivity for the X-axis, the MXR7305V can be
programmed for non-equal sensitivities on the X- and Y-
axes.
Contact Memsic’s local office for additional information.
NC – (pin 5, 4) No connect. These pins can be tied to
common if the application does not allow pins to remain
unconnected.
COM – (pin 3) This is the ground pin for the MXR7305V
CLK – (pin 2) This is an optional serial clock input. The
standard product is delivered with an internal clock (1000
kHz. However, an external clock between 400 kHz and 1.6
MHz can be used as an option, if the sensor is programmed
from the factory to run in external clock mode.
This pin is grounded internally with a 50 Kohm resistor if
an external clock is used it should be able to drive this load.
But if external clock is not used, in order to minimize noise
and ESD this pin should be grounded externally as well.
ST
This pin controls the self-test function of the sensor
Bringing ST
830mV to the Xout and Yout from the 0g value
OUT
Xout
Yout
AOUT
AOUT
Self
Test
IN
– (pin 6)
Y
X
–
(pin 1) Self –Test Input
0 10 20 30 40 50 60 70 80 90 100110
IN
Y-axis acceleration signal output.
high will cause a negative deflection around
Time - millisec
–
.
6/18/2009
.