LIS2DH12 datasheet(18/53 Pages) STMICROELECTRONICS

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Terminology and functionality

LIS2DH12

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DocID025056 Rev 6

3.2.3

6D / 4D orientation detection

The LIS2DH12 provides the capability to detect the orientation of the device in space,

enabling easy implementation of energy-saving procedures and automatic image rotation

for mobile devices.

The 4D detection is a subset of the 6D function especially defined to be implemented in

mobile devices for portrait and landscape computation. In 4D configuration, the Z-axis

position detection is disabled.

3.2.4

“Sleep-to-wake” and “Return-to-sleep”

The LIS2DH12 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 back to the preset normal or high-

resolution mode.

To enable this function the desired threshold value must be stored inside the ACT_THS

(3Eh) register while the duration value is written inside the ACT_DUR (3Fh) register.

When the acceleration falls below the threshold value, the device automatically switches to

low-power mode (10Hz ODR).

During this condition, the ODR[3:0] bits and the LPen bit inside CTRL_REG1 (20h) and the

HR bit in CTRL_REG4 (23h) are not considered.

As soon as the acceleration rises above threshold, the module restores the operating mode

and ODRs as determined by the CTRL_REG1 (20h) and CTRL_REG4 (23h) settings.

3.3

Sensing element

A proprietary process is used to create a surface micromachined accelerometer. The

technology processes 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 traditional packaging techniques, a cap is placed on top of the

sensing element to avoid blocking the moving parts 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.

3.4

IC interface

The complete measurement chain is composed of a low-noise capacitive amplifier which

converts the capacitive unbalance of the MEMS sensor into an analog voltage that will be

available to the user through an analog-to-digital converter.

The acceleration data may be accessed through an I2C/SPI interface, thus making the

device particularly suitable for direct interfacing with a microcontroller.

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