LIS3DETR datasheet(16/46 Pages) STMICROELECTRONICS

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Terminology and functionality

LIS3DE

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DocID023719 Rev 3

When the self-test is activated, the device output level is given by the algebraic sum of the

signals produced by the acceleration acting on the sensor and by the electrostatic test-

force. If the output signals change within the amplitude specified in Table 3, then the sensor

is working properly and the parameters of the interface chip are within the defined

specifications.

3.2.3

6D / 4D orientation detection

The LIS3DE includes 6D / 4D orientation detection.

6D / 4D orientation recognition: In this configuration the interrupt is generated when the

device is stable in a known direction. In 4D configuration Z-axis position detection is

disabled.

3.2.4

Sleep-to-wake and return-to-sleep functions

The LIS3DE can be programmed to automatically switch to low-power mode upon

recognition of a determined event. Once the event condition is over, the device returns to

the preset normal mode.

To enable this function, the desired threshold value must be stored in the Act_THS (3Eh)

registers, while the duration value must be written in the Act_DUR (3Fh) register.

When the acceleration, which is internally high-pass filtered, becomes lower than the

threshold value on all of the three axes, the device automatically switches to low-power

mode (10 Hz ODR).

During this condition, the ODRx bits and LPen bit inside CTRL_REG1 (20h) are not

considered.

Once the acceleration rises above the threshold (at least on one axis), the system restores

the operating mode and ODRs as per the CTRL_REG1 (20h) and CTRL_REG4 (23h)

settings.

3.3

Sensing element

A proprietary process is used to create a surface micro-machined accelerometer. The

technology allows processing suspended silicon structures which are attached to the

substrate in a few points called anchors and are free to move in the direction of the sensed

acceleration. To be compatible with the traditional packaging techniques, a cap is placed on

top of the sensing element to avoid the moving parts from being blocked during the molding

phase of the plastic encapsulation.

When an acceleration is applied to the sensor the proof mass displaces from its nominal

position, causing an imbalance in the capacitive half bridge. This imbalance is measured

using charge integration in response to a voltage pulse applied to the capacitor.

At steady-state the nominal value of the capacitors are a few pF and when an acceleration

is applied, the maximum variation of the capacitive load is in the fF range.

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