LPS33HW accuracy question

[Jacek Pieczaba]

Hello,

I have a question related to accuracy of this sensor see attachment

From the datasheet I can read that the accuracy over temperature is +/2.5hPa. Did I correctly understand that the accuracy of the sensor can change within this range only in this given range of temperatures 0-65C ? But in this case what is the reason to bake in the temperature compensation ?

Second in order to reduce the variation you suggest to run OPC ( one time calibration ) to get better +/- 1hPa accuracy. Could you explain the procedure how this calibration should be done? Any suggestion...

Third question is related to the long time stability which you stating is around +/-1hPa over year. In this case also do you have any recommendation how to address this changes ?

Last observation: all this numbers are connected to 1.8V @ 25C Test conditions. So how this condition are connected with the specified ranges of the temp from 0C to 65C ? Second could you share how input voltage can affect those values ( in my case I am using 3.3V supply instead of 1.8V) ?

Thank you very much in advance

Jacek Pieczaba

[Eleon BORLINI]

Hi @Jacek Pieczaba​ , please find here below our (tentative) answers:

>> From the datasheet I can read that the accuracy over temperature is +/2.5hPa. Did I correctly understand that the accuracy of the sensor can change within this range only in this given range of temperatures 0-65C ? But in this case what is the reason to bake in the temperature compensation?

Yes, you are right. The accuracy refers to that temperature range [0°C, 65°C], which is the full accuracy temperature range. The bake helps to remove residual condensation, especially after soldering process.

>> Second in order to reduce the variation you suggest to run OPC ( one time calibration ) to get better +/- 1hPa accuracy. Could you explain the procedure how this calibration should be done?

To perform the OPC you need a reference pressure sensor (external), to get Pref (see the instructions below). To write the compensated value in the volatile registers follow these steps. Remember that when you restart the device, you have to write again the compensation registers,

1. Set supply to 1.8V for VDD & VDDIO
2. Read Reference pressure in hPa (Pref)
3. Read LPS27HHW pressure in hPa (Pdut)
4. Calculate RPDS = (Pdut-Pref) *16 as Signed 16bit Integer variable
5. Write reg 18h RPDSL (Lower significant RPDS 8bits)
6. Write reg 19h RPDSH (Most significant RPDS 8bits)
7. Verify One point calibration verifying pressure accuracy comparing Pdut and Pref
8. Calculate Pressure Accuracy Pacc=Pdut-Pref
9. If Pacc<0.25hPa, the sensor is calibrated.

>> Third question is related to the long time stability which you stating is around +/-1hPa over year. In this case also do you have any recommendation how to address this changes?

As in case of the one point calibration, you should perform a check with an external reference pressure sensor, and then write the RPDSH registers to compensate the time drift.

>> Last observation: all this numbers are connected to 1.8V @ 25C Test conditions. So how this condition are connected with the specified ranges of the temp from 0C to 65C ? Second could you share how input voltage can affect those values ( in my case I am using 3.3V supply instead of 1.8V) ?

Please consider that all the analog voltage levels inside the ASIC refers to the band-gap voltage, which doesn't vary with the Vdd level (it is always 1.25V). However, being the Vdd related also to the digital voltage levels, the higher the voltage the higher the current consumption and the higher the self-heating of the device. This effect is btw negligible with respect to the above mentioned temperature and time drift.

Regards

[Jacek Pieczaba]

Hello Eleon,

Thank you very much for your kind and clear message. Really appreciate.

With Best Regards,

Jacek Pieczaba