LIS2DHTR datasheet(18/50 Pages) STMICROELECTRONICS

18 / 50 page

Mechanical and electrical specifications

LIS2DH

18/49

Doc ID 022516 Rev 1

2.6.5

6D / 4D orientation detection

The LIS2DH include 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 disable.

2.6.6

“Sleep to wake” and “Return to sleep”

The LIS2DH 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 Act_THS(3Eh)

registers while the duration value written inside Act_DUR(3Fh) registers.

When acceleration module becomes lower than the treshold value, the device automatically

switches to Low power mode (10Hz ODR).

During this condition, ODRx bits and LPen bit inside CTRL_REG1 (20h) and HR bit in

CTRL_REG3 (22h) are not considered.

As soon as the acceleration goes back over the threshold, the systems restores the

operating mode and ODRs as for CTRL_REG1 (20h) and CTRL_REG3 (22h) settings.

2.7

Sensing element

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

technology allows carring 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.

2.8

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 I2C/SPI interface thus making the

device particularly suitable for direct interfacing with a microcontroller.

The LIS2DH features a data-ready signal (RDY) which indicates when a new set of

measured acceleration data is available thus simplifying data synchronization in the digital

system that uses the device.

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