Software
AN4450
24/26
DocID025978 Rev 1
Follow this sequence:
1.
Turn on BOOT bit (bit[7] =1 of CTRL_REG2 (0x21))
2. Wait for the BOOT bit to reset (BOOT bit is self-clearing, it is set again to '0' by
hardware at the end of the process)
3. Wait an additional 5 ms
4. Configure
the
registers
5. Power on the device for normal use
6.7 Absolute
accuracy
drift due to soldering
Reflow soldering may cause a spread of the device population accuracy. The spread is PCB
construction, assembly and layout specific.
Beware that board warping may cause additional drift in the accuracy.
If very good absolute accuracy is required, a one-point calibration in the production line
could be implemented.
6.7.1
Correcting soldering drift (one-point calibration)
The following is a brief guideline to reduce the impact of soldering.
1.
Soldering drift is a complex process and it is not easy to identify the single root cause of
soldering stress.
2. We define the soldering drift as the difference between the accuracy of the pressure
sensor before and after soldering.
3. Soldering temperature profile is one of the major 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 minimize post-soldering drift in SW:
1.
Be sure to re-hydrate the device package by keeping it at 70%RH for 12 h or waiting a
minimum of 36 h at ambient humidity.
2. After point 1, if a residual drift is still present and above the application intended limits,
perform a one-point calibration by following these steps:
a) During board final test use a precision barometer to get the reference value and
calculate the difference with respect to the sensor measurements (taken at
maximum resolution)
b) Store the difference (offset) in the application non-volatile memory
c) Use the offset value to correct all measurements from the sensor
d) Correction can be performed entirely by SW, or the offset value (upper 16-bit only)
can be written in dedicated registers of the sensor (RPDSx), at each power-on, so
that the values read from the sensor are already corrected
e) When the device is calibrated after soldering as proposed above, thanks to the
embedded quadratic compensation, the absolute accuracy is /-1 hPa
f)
The SW offset correction could also take into account for sensor aging test results.
