H3LIS331DL Datasheet, PDF (15/38 Pages) STMicroelectronics – MEMS motion sensor: low-power high-g 3-axis digital accelerometer

H3LIS331DL
3
Functionality
Functionality
The H3LIS331DL is a “nano”, low-power, digital output 3-axis linear accelerometer housed
in an LGA package. The complete device includes a sensing element and an IC interface
able to take the information from the sensing element and to provide a signal to the external
world through an I²C/SPI serial interface.
3.1
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. 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.
3.2
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 that will be
available to the user through an analog-to-digital converter.
The acceleration data may be accessed through an I²C/SPI interface, making the device
particularly suitable for direct interfacing with a microcontroller.
The H3LIS331DL features a data-ready signal (RDY) which indicates when a new set of
measured acceleration data is available, therefore simplifying data synchronization in the
digital system that uses the device.
3.3
Factory calibration
The IC interface is factory calibrated for sensitivity (So) and zero-g level (TyOff).
The trim values are stored inside the device in non-volatile memory. Any time the device is
turned on, the trim parameters are downloaded into the registers to be used during active
operation. This allows the device to be used without further calibration.
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