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iaeinfach
Associate II
May 8, 2019
Question

IIS2DLPC Data Rate Accuracy

The actual sampling rates deviate from the published. For example and ODR of 25Hz is actually ~30Hz. Is this typical? We did not notice this on the IIS2DH part. I expected some variance from the desired rate, but is every device going to vary this much?

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3 replies

iaeinfach
iaeinfachAuthor
Associate II
May 8, 2019

Let me clarify how I measured this. I set the ODR to 25Hz and the FIFO watermark to 25 samples. I measured the time between interrupts on INT1.

25 samples @ 25Hz is actually 44.78Hz.

Eleon BORLINI
ST Employee
May 10, 2019

Hi, no, there should't be such a big distance between set ODR and actual ODR! For a doublechek that everything is correctly running, you could check if the MSb of STATUS (27h) goes to 1 in 1/25 s, polling FIFO_THS bit flag (or FIFO_ FTH in reg FIFO_SAMPLES (2Fh)). Did you set FIFO_CTRL (2Eh) = 19h, right?

Btw, could you share the configuration of the registers you set? Thanks and regards

iaeinfach
iaeinfachAuthor
Associate II
May 10, 2019

In fact, I found the issue to be rather simple. IF_ADD_INC was not enabled. Makes sense now. I am transitioning from the IIS2DH and I have had to adjust some small things like this ensure operation. I missed this one.

Thanks -AP