LIS2DW12TR datasheet(18/66 Pages) STMICROELECTRONICS

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3.3

Sensing element

A proprietary process is used to create a surface micromachined 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. In order 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 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

unbalancing of the MEMS sensor into an analog voltage using 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 LIS2DW12 features a data-ready signal which indicates when a new set of measured acceleration data is

available, thus simplifying data synchronization in the digital system that uses the device.

3.5

Factory calibration

The IC interface is factory-calibrated for sensitivity (So) and Zero-g level offset.

The trim values are stored inside the device in nonvolatile memory. Any time the device is turned on, the trimming

parameters are downloaded into the registers to be used during active operation. This allows using the device

without further calibration. If an accidental write occurs in the registers where trimming parameters are stored, the

BOOT bit in CTRL2 (21h) can help to retrieve the correct trimming parameters from nonvolatile memory without

the need to switch on/off the device. This bit is automatically reset at the end of the download operation. Setting

this bit has no impact on the control registers.

3.6

Temperature sensor

The temperature is available in OUT_T_L (0Dh), OUT_T_H (0Eh) stored as two's complement data, left-justified

in 12-bit mode and in OUT_T (26h) stored as two's complement data, left-justified in 8-bit mode.

Refer to Table 5. Temperature sensor characteristics for the conversion factor.

LIS2DW12

Sensing element

DS11811 - Rev 8

page 18/66

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