ST LPS331AP, Application Note

Page: 21 / 27

AN4159 Software
Doc ID 023639 Rev 3 21/27
“Is the absolute pressure ac/- 1 mbar?”
●
When the LGA are calibrated in final test, yes, it is with absolute accuracy with +/-1 mb
“Registers DELTA_PRESS_xx are not mentioned in the mapping table, and are not well
defined, it is not clear how user has to manage this register (R/W?)”
● From application point of view, we suggest not to touch these registers, as a S/W
subtract can be done at the host place, no matter where the S/W offset data is saved
●
These are R/W registers, which perform a H/W subtraction with the registers
DELTA_PRESS_xx when enabled by bit 1 of CTRL1_REG, before placing the final
result in P_OUT register.
“Is it possible to store the values in a permanent way (after switch off/on)? Any
recommendation on the way to realize calibration?”
●
The S/W offset changes with the weather: The sea level pressure is changing regularly
and in practice is a data coming from the web, so that at system point of view, keeping
this information in
●
The system non-volatile memory maybe the best option.
● The pressure sensor has some free extra rewritable non-volatile memory bytes. This
NVM write option is only for ST-chosen users. It also requires that the VDD is 2.8 V or
higher. A sample reference source code can be provided under LUA.
Case 6:
“What is a recommended way to perform a manual soldering of the LGA package?”
● Apply solder paste (e.g. ALPHA® OM-338-T) on the PCB solder pads using syringe
(air bubble free), and position the LGA accordingly, then, press it, make sure it is flat on
PCB, then heat up in the over using 260C JDEC profile.
● First, remember that Hand solder is out of spec. Otherwise, coat your solder pad with
tin-lead, then use solder wick to flatten the solder ball, then put solder iron on the LGA
land marks to deposit solder on LGA pads. Then, position it, and use hot air gun to melt
both sides and get eutectic bonding (350 °C). This is not recommended. Hot air gun
must be spread around the LGA dynamically: Keep moving the air gun around the LGA.
Case 7:
“What is the consumption of the one shot read? For configuration at .04, 0.025 and
.02 mbar?”
● One acquisition per second:
– Accuracy = 0.04, current consumption = 25 µA
– Accuracy = 0.025, current consumption = 27 µA
– Accuracy = 0.025, current consumption = 30 µA
The power consumption is linear with the number of acquisition. It means that if they use
1/3 Hz the above numbers have to divide by 3:
● One acquisition per 1/3 second:
– Accuracy = 0.04, current consumption = 8.3 µA
– Accuracy = 0.025, current consumption = 9 µA
– Accuracy = 0.025, current consumption = 10 µA
Wake-up time from power-down to normal mode?
●
1 msec