lis3l02as5 STMicroelectronics, lis3l02as5 Datasheet - Page 9

• Manufacturer Part Number: lis3l02as5
• Description: Mems Inertial Sensor 3-axis - ??2g/6g Linear Accelerometer
• Manufacturer: STMicroelectronics

LIS3L02AS5
3
3.1
3.2
3.3
Functionality
The LIS3L02AS5 is a high performance, low-power, analog output three axes linear
accelerometer packaged in a SO24 package. The complete device includes a sensing element
and an IC interface able to take the information from the sensing element and to provide an
analog signal to the external world.
Sensing element
A proprietary process is used 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 in the direction of the sensed acceleration.
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 moulding 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 sense capacitor.
At steady state the nominal value of the capacitors are few pF and when an acceleration is
applied the maximum variation of the capacitive load is up to 100fF.
IC Interface
In order to increase robustness and immunity against external disturbances the complete signal
processing chain uses a fully differential structure. The final stage converts the differential
signal into a single-ended one to be compatible with the external world.
The signals of the sensing element are multiplexed and fed into a low-noise capacitive charge
amplifier that implements a Correlated Double Sampling (CDS) at its output to cancel the offset
and the 1/f noise. The output signal is de-multiplexed and transferred to three different S&Hs,
one for each channel and made available to the outside.
The low noise input amplifier operates at 200 kHz while the three S&Hs operate at a sampling
frequency of 66 kHz. This allows a large oversampling ratio, which leads to in-band noise
reduction and to an accurate output waveform.
All the analog parameters (zero-g level, sensitivity and self-test) are ratiometric to the supply
voltage. Increasing or decreasing the supply voltage, the sensitivity and the offset will increase
or decrease almost linearly. The self test voltage change varies cubically with the supply
voltage.
Factory calibration
The IC interface is factory calibrated for Sensitivity (So) and Zero-g Level (Voff). 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
operation. This allows the user to employ the device without further calibration.
3 Functionality
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