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Mechanical design

 rules 

AN4672 

 

8/24 

DocID027655 Rev 3 

 

 

Figure 2: Pressure sensor integration and embodiment reference 

 

 

 

A different implementation , more expensive but more efficient in terms of sensing 
performances is the design with an air flow structure, described i

Figure 3: "Pressure 

sensor integration and embodiment with vent channel"

. The design with multiple vent 

apertures is a more expensive solution, but providing , depending on the design 
specifications, a faster response time. 

Figure 3: Pressure sensor integration and embodiment with vent channel 

 

 

It is useful to underline that the sensor can work properly even if it is placed in customer's 
application system without considering any dedicated hole (vent aperture) unless that one 
is not hermetically sealed. The design guidelines reported above are for getting out top 
performances. 

2.1.2 

Heat propagation 

The presence of heating sources near the sensor can deteriorate the performances by 
modifying pressure and temperature measurement as well as generating thermal gradients 
around the sensing area affecting the correct measurement in static and dynamic 
conditions. 

We report design guidelines for avoiding this effect, but, we remark that the increasing 
temperature impacts on performances and is strongly attenuated by the embedded 
temperature compensation of LPS22HB and LPS25HB devices.  

Содержание LPS22HB

Страница 1: ...LPS25HB digital pressure sensors hardware guidelines for system integration Introduction The purpose of this application note is to introduce guidelines for the hardware integration of STMicroelectron...

Страница 2: ...Heat propagation 8 2 1 3 Mechanical stress 12 2 2 Sensor embodiment and housing 13 2 3 Sensor protection 15 3 Reference design integration and housing on a personal device 16 4 Use case and configura...

Страница 3: ...onfiguration 18 Table 2 FIFO mode selection 19 Table 3 ODR configuration 20 Table 4 Temperature resolution configuration 21 Table 5 FIFO coefficient filter 21 Table 6 FIFO MEAN MODE configurations for...

Страница 4: ...n the PCB 11 Figure 8 Sensor wiring with wrong placement on the PCB 11 Figure 9 Bad configuration for mechanical stress a 12 Figure 10 Bad configuration for mechanical stress b 12 Figure 11 Good confi...

Страница 5: ...ressure sensor system integration Therefore in order to get a reliable and consistent measurement all the parameters involved in the mechanical design must be dimensioned to get the maximum sensor exp...

Страница 6: ...ation consists of determining 1 the placement of the sensor in the system 2 the sensor embodiment and housing 3 sensor protection from dust water or chemical solvent by a sensor chamber in presence of...

Страница 7: ...sensor integration design the overall response time will be modified and the final performance shall match the target specifications In general target is to avoid design with a response time lower th...

Страница 8: ...line that the sensor can work properly even if it is placed in customer s application system without considering any dedicated hole vent aperture unless that one is not hermetically sealed The design...

Страница 9: ...tween the environment and the dead volume inside the system Therefore the sensor has to be placed at the correct distance from these sources and to guarantee the appropriate isolation it is recommende...

Страница 10: ...sources avoiding metal areas near and under the device A good design rule is provided in Figure 6 Sensor with a correct sensor placement on the PCB to get the appropriate isolation from heat sources...

Страница 11: ...uction In Figure 8 Sensor wiring with wrong placement on the PCB the wrong placement of the sensor close to a device generating too much heating deteriorates the sensor performance Figure 8 Sensor wir...

Страница 12: ...nsor direct due to a wrong mechanical system design or indirect due to the user interaction with the system like in the case of wearable or portable device Figure 9 Bad configuration for mechanical st...

Страница 13: ...hlighted above for the sensor placement and on top of that has to provide all the features of specific application like waterproof water resistant or resistant to harsh environment in case it is requi...

Страница 14: ...with the external environment under test that results in a higher efficiency in terms of response time and an extremely small dead volume In this example the vent apertures size is an order magnitude...

Страница 15: ...water proof application The key parameter for this kind of implementation is the appropriate choice of the membrane according to the design requirements and taking into account that the membrane mater...

Страница 16: ...wo vent apertures covered with filter membranes This solution provides at the same time an efficient response time and a good protection from dust and light In case of waterproof device a sensor chamb...

Страница 17: ...AN4672 Reference design integration and housing on a personal device DocID027655 Rev 3 17 24 Figure 17 Device integration reference in a portable device...

Страница 18: ...d in table Table 1 ODR configuration ODR2 ODR1 ODR0 Pressure Hz Temperature Hz 0 0 0 One shot 0 0 1 1 Hz 1 Hz 0 1 0 10 Hz 10 Hz 0 1 1 25 Hz 25 Hz 1 0 0 50 Hz 50 Hz 1 0 1 75 Hz 75 Hz At device boot the...

Страница 19: ...nificant data out from the FIFO This buffer can work according to seven different modes as described in table 1 The FIFO buffer is enabled when the FIFO_EN bit in CTRL_REG2 11h is set to 1 and each mo...

Страница 20: ...bits of CTRL_REG1 0x20 as described in table Table 3 ODR configuration ODR2 ODR1 ODR0 Pressure Hz Temperature Hz 0 0 0 One shot 0 0 1 1 Hz 1 Hz 0 1 0 7 Hz 7 Hz 0 1 1 12 5 Hz 12 5 Hz 1 0 0 25 Hz 25 Hz...

Страница 21: ...0 32 1 1 64 In addition to further improve the resolution by changing the noise figure the hardware moving average filter can be utilized by setting the FIFO mean mode FIFO_CTRL 0x2E bits F_MODE 2 0...

Страница 22: ...gh resolution 32 512 64 25 0 008 Portable device dynamic Very high resolution 16 512 64 25 0 011 Portable device Low Power High resolution 8 512 64 25 0 015 Elevator Floor change detection Standard re...

Страница 23: ...3 24 6 Revision history Table 7 Document revision history Date Revision Changes 20 Aug 2015 1 Initial release 16 Dec 2015 2 Document updated to include LPS22HB 02 Aug 2016 3 Updated Section 4 Use case...

Страница 24: ...sers are solely responsible for the choice selection and use of ST products and ST assumes no liability for application assistance or the design of Purchasers products No license express or implied to...

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