MMA7455L Просмотр технического описания (PDF) - Freescale Semiconductor

Номер в каталоге

Компоненты Описание

производитель

MMA7455L

±2g/±4g/±8g Three Axis Low-g Digital Output Accelerometer

Freescale Semiconductor 

Table 4. Function Parameters for Detection

–40°C < TA < 85°C, 2.4 V < AVDD < 3.6 V, unless otherwise specified

Characteristic

Symbol

Min

Typ

Max

Level Detection

Detection Threshold Range

0

—

FS

Pulse Detection

Pulse detection range (Adjustable range)

0.5

—

127

Time step for pulse detection

—

0.5

—

Threshold range for pulses

0

—

FS

Detection levels for threshold

—

127

—

Latency timer (Adjustable range)

1

—

150

Time Window (Adjustable range)

1

—

250

Bandwidth for detecting interrupt*

—

600

—

Time step for latency timer and time window

—

1

—

Note: The response time is between 10% of full scale VDD input voltage and 90% of the final operating output voltage.

*The bandwidth for detecting interrupts in level and pulse is 600Hz which is changed from measurement mode.

Unit

g

ms

ms

g

Counts

ms

ms

Hz

ms

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 (Figure 3).

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 (Figure 3). As the center beam moves with acceleration, the distance

between the beams changes and each capacitor's value will change, (C = Aε/D). Where A is the area of the beam, ε is the di-

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.

Acceleration

Figure 3. Simplified Transducer Physical Model

MMA7455L

8

Sensors

Freescale Semiconductor

Share Link: