MMA7455LT Freescale Semiconductor, MMA7455LT Datasheet - Page 8

• Manufacturer Part Number: MMA7455LT
• Description: Board Mount Accelerometers 3-AXIS DIGITAL 2 4 8G
• Manufacturer: Freescale Semiconductor

Specifications of MMA7455LT

• Sensing Axis: X, Y, Z
• Acceleration: 2 g, 4 g, 8 g
• Supply Voltage (max): 3.6 V
• Supply Voltage (min): 2.4 V
• Supply Current: 400 uA
• Maximum Operating Temperature: + 85 C
• Minimum Operating Temperature: - 40 C
• Sensitivity: 64 LSB/g
• Package / Case: LGA-14
• Output Type: Digital
• Acceleration Range: ± 2g, ± 4g, ± 8g
• No. Of Axes: 3
• Sensor Case Style: LGA
• No. Of Pins: 14
• Supply Voltage Range: 2.4V To 3.6V
• Operating Temperature Range: -40°C To +85°C
• Filter Terminals: SMD
• Rohs Compliant: Yes
• Ic Interface Type: I2C, SPI
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Note: The response time is between 10% of full scale V
*The bandwidth for detecting interrupts in level and pulse is 600Hz which is changed from measurement mode.
PRINCIPLE OF OPERATION
The Freescale accelerometer is a surface-micromachined integrated-circuit accelerometer. The device consists of a surface mi-
cromachined capacitive sensing cell (g-cell) and a signal conditioning ASIC contained in a single package. The sensing element
is sealed hermetically at the wafer level using a bulk micromachined cap wafer. The g-cell is a mechanical structure formed from
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
As the beams attached to the central mass move, the 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 accel-
eration. The g-cell beams form two back-to-back capacitors
between the beams changes and each capacitor's value will change, (C = A
electric constant, and D is the distance between the beams.
The ASIC uses switched capacitor techniques to measure the g-cell capacitors and extract the acceleration data from the differ-
ence between the two capacitors. The ASIC also signal conditions and filters (switched capacitor) the signal, providing a digital
output that is proportional to acceleration.
Table 4. Function Parameters for Detection
–40°C < T
8
MMA7455L
Level Detection
Pulse Detection
Detection Threshold Range
Pulse detection range (Adjustable range)
Time step for pulse detection
Threshold range for pulses
Detection levels for threshold
Latency timer (Adjustable range)
Time Window (Adjustable range)
Bandwidth for detecting interrupt*
Time step for latency timer and time window
A
< 85°C, 2.4 V < AV
Characteristic
DD
< 3.6 V, unless otherwise specified
Figure 3. Simplified Transducer Physical Model
DD
input voltage and 90% of the final operating output voltage.
Acceleration
(Figure
(Figure
3).
3). As the center beam moves with acceleration, the distance
Symbol
ε
/D). Where A is the area of the beam,
Min
0.5
—
—
—
—
0
0
1
1
Typ
127
600
0.5
—
—
—
—
—
1
Freescale Semiconductor
Max
127
150
250
FS
FS
—
—
—
—
ε
is the di-
Counts
Unit
Sensors
ms
ms
ms
ms
ms
Hz
g
g