FXAS21002 Self Test Function

[nc1]

I'm having some trouble understanding the self test function on the FXAS21002. The datasheet shows a self-test output change of [min, typ, max] = [7000, 16000, 25000] for CTRL_REG0[FS] = 00. With this in mind, a few questions:

1. Should this be interpreted as a stable, constant offset from zero rate? (i.e., should X, Y and Z ideally output a stable 16000LSB when the device is configured for self test operation?)
2. Why such a large variation between min (7000) and max (25000)?
3. Is it safe to assume similar min, typ and max STOC values for different full-scale range configurations?
4. Should there be some correlation between X, Y and Z?
5. The unit I'm currently working with outputs a constant [X,Y,Z]=[~5700,~18200, ~15650] LSB. I'm not sure how to interpret this information. The X-axis output is well below the min of 7000. Does this mean the unit is faulty?

Thank you in advance!

[nc1]

Hi Tomas,

Thank you for the feedback.

Yes this is for one part only. We've only tested a few, but the others output around 14000-17000 in all axes.

We've not yet had the opportunity to test the defective unit with accurate rate stimuli (rate table or similar), but the output during normal operation seems to be in the correct ball park. I'm trying to gauge whether this self test function should be interpreted as a pass/fail or merely as a indicator that a transducer might be defective?

Regards, Nico

[TomasVaverka]

Hi Nico,

I need to double check this with our Design team. I will update this thread as soon as I have their feedback.

Thanks for your patience.

Best regards,

Tomas

[TomasVaverka]

Hi Nico,

Here are the answers to your questions:

1. Yes, it should be pretty stable values (including some noise) within the specified range.

2. It is a wide range because the self-test output is not trimmed and the purpose of the self-test for this product is just to check if the transducer is working and the signal chain is functioning.

3. The self-test feature is meant only for FS Range = 00. For all other FS values the out is maxed out and is not valid.

4. No.

5. Provided the CTRL_REG0[FS] = 00 and the part is stationary, the X value should be within limits. Is this observation for 1 part only? 

Best regards,

Tomas