Does HP_REF_MODE in lis2dw12 have any effect if FDS in CTRL6 is set to 0 (low-pass filter path selected)?

[MBoch.2]

From this picture in application note looks like HP_REF_MODE  should not have any effect to the output data when purple path is selected.

But in tests we see differences in output data with and without HP_REF_MODE set to 1.

[Federica Bossi]

Hi @MBoch.2​ ,

Welcome to ST Community 🙂

When you enable the HP_REF_MODE  bit, the output data is calculated as the difference between the measured acceleration and the output values captured when reference mode was enabled. In this way only the difference is applied without any filtering.

However, setting this bit to '1' makes sense only when you are in the HP path (the blue one in the AN graph).

When you are in the purple path you don't need to activate the HP_REF_MODE.

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[MBoch.2]

Thanks for answer, but this is still not clear for me what is happening if HP_REF_MODE is set for purple path on the picture. I'm interesting what will be the real affect to the output data in this particular case. The documentation says everything about the combination HPF and HP_REF_MODE, but nothing about HP_REF_MODE in case of LPF.  Indirectly from the picture it seems for me that it suppose to be ignored if purple path (low-pass filter) is selected, but from actual data I see that it has an effect, and actual data not really matches to the description of HP_REF_MODE  for HP, while for HP mode the HP_REF_MODE  works as expected.

[Federica Bossi · Accepted solution]

Hi @MBoch.2​ ,

The documentation doesn't say anything about HP_REF_MODE in case of LPF because this is not a possible configuration, so if you use that bit in the purple path you will get inconsistent results. If you want that the HP_REF_MODE works as expected you have to be in the blue path.

Thank you for pointing out that the image in the AN may be confusing, we will edit it or explicitly write not to set HP_REF_MODE for LPF.

Please click on Select as Best at the bottom of this post to help other users with the same issue to find the answer faster 🙂