LPS35HW datasheet(13/48 Pages) STMICROELECTRONICS

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LPS35HW

Functionality

DocID029129 Rev 1

13/48

Functionality

The LPS35HW is a high resolution, digital output pressure sensor packaged in an HLGA

full- mold package. The complete device includes a sensing element based on a

piezoresistive Wheatstone bridge approach, and an IC interface which communicates a

digital signal from the sensing element to the application.

3.1

Sensing element

An ST proprietary process is used to obtain a silicon membrane for MEMS pressure

sensors. When pressure is applied, the membrane deflection induces an imbalance in the

Wheatstone bridge piezoresistances whose output signal is converted by the IC interface.

3.2

IC interface

The complete measurement chain is composed of a low-noise amplifier which converts the

resistance unbalance of the MEMS sensors (pressure and temperature) into an analog

voltage using an analog-to-digital converter. The pressure and temperature data may be

accessed through an I²C/SPI interface thus making the device particularly suitable for direct

interfacing with a microcontroller. The LPS35HW features a Data-Ready signal which

indicates when a new set of measured pressure and temperature data are available, thus

simplifying data synchronization in the digital system that uses the device.

3.3

Factory calibration

The trimming values are stored inside the device in a non-volatile structure. When the

device is turned on, the trimming parameters are downloaded into the registers to be

employed during the normal operation which allows the device to be used without requiring

any further calibration.

3.4

How to interpret pressure readings

The pressure data are stored 3 registers: PRESS_OUT_H (2Ah), PRESS_OUT_L (29h),

and PRESS_OUT_XL (28h). The value is expressed as 2’s complement. To obtain the

pressure in hPa, take the two’s complement of the complete word and then divide by

4096LSB/hPa.

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