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LIS3L02DQ
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4 Functionality
4.1 Sensing element
A proprietary process is utilized to create a surface micro-machined accelerometer. The technology allows
to carry out suspended silicon structures which are attached to the substrate in a few points called anchors
and are free to move on a plane parallel to the substrate itself. To be compatible with the traditional pack-
aging 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, 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 sense capacitors.
The nominal value of the capacitors, at steady state, are a few pF and when an acceleration is applied the
maximum variation of the capacitive load is up to 100 fF.
4.2 IC Interface
The complete measurement chain is composed of a low-noise capacitive charge amplifier which converts
the capacitive unbalanced signal of the MEMS sensor into an analog voltage. Three Σ∆ analog-to-digital
converters, one for each axis, translate the signal into a digital bitstream.
The Σ∆ converters are tightly coupled with dedicated reconstruction filters which remove the high frequen-
cy components of the quantization noise and provide high resolution digital words.
The charge amplifier and the Σ∆ converters are operated at 107.5 kHz and 35.8 kHz.
The data rate at the output of the reconstruction filters depends on the user selected Decimation Factors
(DF) and are selectable from 280 Hz to 4.48 kHz.
The acceleration data may be accessed through an I
2
C/SPI interface thus making the device particularly
suitable for direct interfacing with a microcontroller.
The LIS3L02DQ features a Data-Ready signal (RDY) which indicates when a new set of measured accel-
eration data is available thus simplifying data synchronization in digital systems.
The LIS3L02DQ may also be configured to generate an inertial wake-up/interrupt signal when a program-
mable acceleration threshold is exceeded along one of the three axes.
4.3 Factory calibration
The IC interface is factory calibrated to provide a ready to use device. The parameters which are trimmed
are: gain, offset, common mode and internal clock frequency.
The trimming values are stored inside the device by a non volatile structure. Any time the device is turned
on, the trimming parameters are downloaded into the registers to be employed during the normal opera-
tion.This allows the user to employ the device without any further calibration.
