IIS2DLPCTR datasheet(25/69 Pages) STMICROELECTRONICS

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IIS2DLPC

Terminology and functionality

3.2.5

High tap/double-tap user configurability

The device embeds the possibility to select the following parameters:



single axis or multiple axes in TAP_THS_Z (32h)



axis priority in TAP_THS_Y (31h)



threshold value of each axis in TAP_THS_X (30h), TAP_THS_Y (31h), and

TAP_THS_Z (32h)



max time threshold between 2 consecutive taps for double-tap recognition, min time

threshold between 2 consecutive taps to detect a new tap event in INT_DUR (33h)

3.2.6

Offset management

The user can manage offset in the output or for wakeup detection using dedicated

embedded hardware (see Section 5.1: Block diagram of filters).

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 IIS2DLPC 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.

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