MMA3202EG Freescale, MMA3202EG Datasheet - Page 4

• Manufacturer Part Number: MMA3202EG
• Manufacturer: Freescale

Specifications of MMA3202EG

• Family Name: MMA3202
• Package Type: SOIC W
• Operating Supply Voltage (min): 4.75V
• Operating Supply Voltage (typ): 5V
• Operating Supply Voltage (max): 5.25V
• Operating Temperature (min): -40C
• Operating Temperature (max): 125C
• Operating Temperature Classification: Automotive
• Product Height (mm): 3.3mm
• Mounting: Surface Mount
• Pin Count: 20
• Lead Free Status / RoHS Status: Compliant

surface-micromachined integrated-circuit accelerometer.
capacitive sensing cell (g-cell) and a CMOS signal
conditioning ASIC contained in a single integrated circuit
package. The sensing element is sealed hermetically at the
wafer level using a bulk micromachined “cap'' wafer.
semiconductor materials (polysilicon) using semiconductor
processes (masking and etching). It can be modeled as a set
of beams attached to a movable central mass that move
between fixed beams. The movable beams can be deflected
from their rest position by subjecting the system to an
acceleration
distance from them to the fixed beams on one side will
increase by the same amount that the distance to the fixed
beams on the other side decreases. The change in distance
is a measure of acceleration.
(Figure
distance between the beams change and each capacitor's
value will change, (C = NAε/D). Where A is the area of the
facing side of the beam, ε is the dielectric constant, D is the
Filtering
contain an onboard 4-pole switched capacitor filter. A Bessel
implementation is used because it provides a maximally flat
delay response (linear phase) thus preserving pulse shape
integrity. Because the filter is realized using switched
capacitor techniques, there is no requirement for external
passive components (resistors and capacitors) to set the cut-
off frequency.
Self-Test
verification of the mechanical and electrical integrity of the
accelerometer at any time before or after installation. This
feature is critical in applications such as automotive airbag
systems where system integrity must be ensured over the life
of the vehicle. A fourth “plate'' is used in the g-cell as a self-
test plate. When the user applies a logic high input to the self-
test pin, a calibrated potential is applied across the self-test
plate and the moveable plate. The resulting electrostatic
force (Fe =
resultant deflection is measured by the accelerometer's
control ASIC and a proportional output voltage results. This
procedure assures that both the mechanical (g-cell) and
electronic sections of the accelerometer are functioning.
MMA3202KEG
4
The Freescale Semiconductor, Inc. accelerometer is a
The device consists of a surface micromachined
The g-cell is a mechanical structure formed from
As the beams attached to the central mass move, the
The g-cell beams form two back-to-back capacitors
The Freescale Semiconductor, Inc. accelerometers
The sensor provides a self-test feature that allows the
3). As the central mass moves with acceleration, the
1
/
(Figure
2
AV
2
/d
2
3).
) causes the center plate to deflect. The
PRINCIPLE OF OPERATION
SPECIAL FEATURES
distance between the beams, and N is the number of beams.
The X-Y device contains two structures at right angles to
each other.
measure the g-cell capacitors and extract the acceleration
data from the difference between the two capacitors. The
ASIC also signal conditions and filters (switched capacitor)
the signal, providing a high level output voltage that is
ratiometric and proportional to acceleration.
Ratiometricity
and sensitivity will scale linearly with applied supply voltage.
That is, as you increase supply voltage the sensitivity and
offset increase linearly; as supply voltage decreases, offset
and sensitivity decrease linearly. This is a key feature when
interfacing to a microcontroller or an A/D converter because
it provides system level cancellation of supply induced errors
in the analog to digital conversion process.
Status
and a fault latch. The Status pin is an output from the fault
latch, OR'd with self-test, and is set high whenever one (or
more) of the following events occur:
•
•
•
input pin, unless one (or more) of the fault conditions
continues to exist.
The CMOS ASIC uses switched capacitor techniques to
Ratiometricity simply means that the output offset voltage
Freescale accelerometers include fault detection circuitry
The fault latch can be reset by a rising edge on the self-test
Supply voltage falls below the Low Voltage Detect (LVD)
voltage threshold
Clock oscillator falls below the clock monitor minimum
frequency
Parity of the EPROM bits becomes odd in number.
Figure 3. Simplified Transducer Physical Model
Acceleration
Freescale Semiconductor
Sensors