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April 2014

DocID025978 Rev 1

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AN4450

Application note

Hardware and software guidelines for use of LPS25H pressure

sensor

By Raffaele Di Vaio

Introduction

The LPS25H is an ultra-compact absolute piezoresistive pressure sensor with enhanced
digital features in a small package footprint.

Unless specifically noted, all recommendations in this document apply only to the LPS25H.

Please refer to the LPS25H datasheet (available at www.st.com) for device and feature
definitions.

www.st.com

Содержание LPS25H

Страница 1: ...io Introduction The LPS25H is an ultra compact absolute piezoresistive pressure sensor with enhanced digital features in a small package footprint Unless specifically noted all recommendations in this...

Страница 2: ...low power consumption 14 4 Using the device step by step from basic to advanced 15 4 1 First time bring up I C example 15 4 2 Quick troubleshooting guide 15 4 3 One shot mode measurement sequence 16...

Страница 3: ...mation 22 6 3 Reference SW to get started with LPS25H 22 6 4 Pressure to altitude conversion 22 6 5 SW filtering internal FIFO 23 6 6 Reset the device to power on configuration 23 6 7 Absolute accurac...

Страница 4: ...tween the sensor and a PC on which it is possible to use the downloadable graphical user interface GUI from ST Unico SW or dedicated software routines for customized applications A plain terminal such...

Страница 5: ...MS Windows based SW application called Unico This tool may be used as a simple real time demonstrator or to verify device performance It also allows easy monitoring of the register status and allows...

Страница 6: ...2 Hardware designing PCB schematics and layout 2 1 LPS25H device package interconnect and polarization 2 1 1 Package drawings Pressure sensor LPS25H is available in a holed LGA package HCLGA 10L 1mm t...

Страница 7: ...SDA SDI SDIO I C serial data SDA 4 wire SPI serial data input SDI 3 wire SPI serial data input output SDIO Optional pull up resistor connected to VDD_IO could be required for I C see I C standard for...

Страница 8: ...lower than VDD In the example shown here VDD_IO is connected to VDD Please note that the LPS25H does not have an internal pull up on the I C lines SCL and SDA They must be added externally according t...

Страница 9: ...er exposure condensation GORE TEX protection etc The HCLGA package is compliant with the ECOPACK standard and is qualified for soldering heat resistance according to JEDEC J STD 020 2 2 1 PCB design r...

Страница 10: ...mended for screen printing The final soldering paste thickness should allow proper cleaning of flux residues and clearance between sensor package and PCB Stencil aperture should have a rectangular sha...

Страница 11: ...bubble free and position the LGA accordingly Then press it to ensure it is flat on the PCB and heat it in an oven using the 260 C JDEC profile the one shown in Figure 7 Take care that hand soldering i...

Страница 12: ...ration data This is triggered by VDD increasing above 1 6 V Current consumption during the device initialization peaks around 200 A for a duration of about 600 s After these steps the LPS25H will ente...

Страница 13: ...64 Idd 661 A Vdd independent at first approximation b Example 2 ODR 1 Hz Pavg pressure average 512 Tavg temperature average 64 Idd 26 4 A c Example 3 ODR 1 Hz Pavg pressure average 8 Tavg temperature...

Страница 14: ...e internal circuit in undefined state creating introducing extra power consumption Connect unused input pins such as CS and SA0 if a single sensor is used on the I2C bus to VDD_IO Use a pull up resist...

Страница 15: ...If the device is not communicating properly on the I C bus 1 If the I C slave address is not acknowledged check Power supply is present and matches the I C master VDD_IO I C line pull ups are present...

Страница 16: ...E07C means 42 5 8068 480 25 7 C as reference 0x6BD0 100 C 0xB050 0 C The value read from the PRESS_OUT registers is always the difference of the sensor measured pressure after averaging and a base val...

Страница 17: ...eparately from pressure data The temperature readout is always referred to the last pressure data in the FIFO as no FIFO is available for temperature data The register auto increment rounding is then...

Страница 18: ...are stored in the buffer before being available in PRESS_OUT_XL PRESS_OUT_L and PRESS_OUT_H On the contrary of FIFO mode when full the FIFO discards the older data as the new arrive An interrupt can...

Страница 19: ...ate at 1 Hz As soon as FIFO Mean mode is set the buffer is cleaned 5 1 6 Hardware digital filter To achieve the final averaging an HW digital filter is used Table 3 Number of averaged samples vs WTM_P...

Страница 20: ...consumption while keeping a low noise figure the recommendation is to reduce the pressure and temperature averaging reduce ODR to minimum and enable the digital filter FIFO For example RES_CONF 0x10...

Страница 21: ...he FIFO works in Stream mode till a trigger event occurs then it changes to FIFO mode 5 2 2 Bypass to Stream mode F_MODE 2 0 100 in FIFO_CTRL 0x2E The FIFO is in Bypass mode so it stays empty because...

Страница 22: ...mpletion Section 4 3 The INT1 pin can be used as event to minimize serial bus polling 6 2 One shot mode conversion time estimation Typical conversion time 62 Pavg Tavg 975 s ex Tavg 64 Pavg 512 Typ co...

Страница 23: ...ilter could be implemented on the sensor measurements The internal FIFO buffer and HW filter can also be used as indicated in previous sections this is strongly suggested since it reduces the level of...

Страница 24: ...or contributors to soldering shift 4 A well controlled temperature soldering profile that avoids peak temperature over the max JEDEC spec can reduce the accuracy drift Here some hints on how to minimi...

Страница 25: ...DocID025978 Rev 1 25 26 AN4450 Revision history 26 7 Revision history Table 5 Document revision history Date Revision Changes 29 Apr 2014 1 Initial release...

Страница 26: ...PYRIGHT OR OTHER INTELLECTUAL PROPERTY RIGHT ST PRODUCTS ARE NOT DESIGNED OR AUTHORIZED FOR USE IN A SAFETY CRITICAL APPLICATIONS SUCH AS LIFE SUPPORTING ACTIVE IMPLANTED DEVICES OR SYSTEMS WITH PRODU...

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