Datasheet

Terminology and functionality LIS3DH
18/54 DocID17530 Rev 2
3.2.3 6D / 4D orientation detection
The LIS3DH 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 LIS3DH 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 (10 Hz 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 micro-machined accelerometer. The
technology allows carrying out 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 blocking the moving parts during the moulding 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 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 by a low-noise capacitive amplifier which
converts the capacitive unbalancing of the MEMS sensor into an analog voltage that is
finally available to the user by 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.