MMA1213EG Freescale, MMA1213EG Datasheet - Page 4

• Manufacturer Part Number: MMA1213EG
• Manufacturer: Freescale

Specifications of MMA1213EG

• Family Name: MMA1213
• Package Type: SOIC
• 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: 16
• Lead Free Status / RoHS Status: Compliant

MMA1213D
4
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 (poly silicon) using semiconductor
processes (masking and etching). It can be modeled as two
stationary plates with a moveable plate in-between. The
center plate can be deflected from its rest position by
subjecting the system to an acceleration
fixed plate will increase by the same amount that the distance
to the other plate decreases. The change in distance is a
measure of acceleration.
(Figure
distance between the plates changes and each capacitor's
value will change, (C = Aε/D). Where A is the area of the
plate, ε is the dielectric constant, and D is the distance
between the plates.
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.
The Freescale accelerometer is a surface-micromachined
The device consists of a surface micromachined
The g-cell is a mechanical structure formed from
When the center plate deflects, the distance from it to one
The g-cell plates form two back-to-back capacitors
The CMOS ASIC uses switched capacitor techniques to
Figure 3. Transducer
Physical Model
4). As the center plate moves with acceleration, the
Acceleration
Figure 4. Equivalent
Circuit Model
(Figure
PRINCIPLE OF OPERATION
3).
Filtering
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 air bag
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.
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 Freescale accelerometers contain an on board 4-pole
The sensor provides a self-test feature that allows the
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.
1
/
2
AV
2
/d
SPECIAL FEATURES
2
) causes the center plate to deflect. The
Freescale Semiconductor
Sensors