Functionality LPS331AP
8/36 Doc ID 022112 Rev 7
3 Functionality
The LPS331AP is a high resolution, digital output pressure sensor packaged in an HCLGA
holed package. The complete device includes a sensing element based on a piezoresistive
Wheatstone bridge approach, and an IC interface able to take the information from the
sensing element to the external world, as a digital signal.
3.1 Sensing element
An ST proprietary process is used to obtain a mono-silicon µ-sized membrane for MEMS
pressure sensors, without requiring substrate to substrate bonding. When pressure is
applied, the membrane deflection induces an imbalance in the Wheatstone bridge
piezoresistances, whose output signal is converted by the IC interface.
Intrinsic mechanical stoppers prevent breakage in case of pressure overstress, ensuring
measurement repeatability.
The pressure inside the buried cavity under the membrane is constant and controlled by
process parameters.
3.2 IC interface
The complete measurement chain consists of a low-noise capacitive amplifier, which
converts the resistive unbalance of the MEMS sensor into an analog voltage signal, and of
an analog-to-digital converter, which translates the produced signal into a digital bitstream.
The converter is coupled with a dedicated reconstruction filter which removes the high
frequency components of the quantization noise and provides low rate and high resolution
digital words.
The pressure data can be accessed through an I
2
C/SPI interface making the device
particularly suitable for direct interfacing with a microcontroller.
3.3 Factory calibration
The IC interface is factory calibrated at three temperatures and two pressures for sensitivity
and accuracy.
The trimming values are stored inside the device by a non-volatile structure. Whenever the
device is turned on, the trimming parameters are downloaded into the registers to be
employed during normal operation. This allows the user to employ the device without
requiring any further calibration.
