Datasheet

Terminology and functionality LIS2DH12
18/53 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 I
2
C/SPI interface, thus making the
device particularly suitable for direct interfacing with a microcontroller.