MIS2DH datasheet(18/49 Pages) STMICROELECTRONICS

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Mechanical and electrical specifications

MIS2DH

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DocID027506 Rev 2

6D / 4D orientation recognition

In this configuration the interrupt is generated when the device is stable in a known

direction. In 4D configuration, detection of the position of the Z-axis is disabled.

2.6.6

“Sleep-to-wake” and “Return-to-sleep”

The MIS2DH 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)

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_REG3 (22h) 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_REG3 (22h) settings.

2.7

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.

2.8

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 I2C/SPI interface, thus making the

device particularly suitable for direct interfacing with a microcontroller.

The MIS2DH features a data-ready signal (DRDY) which indicates when a new set of

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

system that uses the device.

The MIS2DH may also be configured to generate an inertial wake-up and free-fall interrupt

signal according to a programmed acceleration event along the enabled axes. Both free-fall

and wake-up can be available simultaneously on two different pins.

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