Functionality

LPS331AP

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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.

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.