Very strange power profile on LSM6DSL

[gutzchi]

Good morning.

We are testing several motion sensors for a commercial medical wristband. We have selected the LSM6DSL to evaluate its suitability. However, we have detected a very strange power consumption pattern. The VCC pin consumes as expected an average of 40uA:

Nevertheless, the consumption of the VDDIO is rather strange. The consumption due to the actual communication every two seconds is represented by the small wedge of around 100ms in the middle of the low power consumption interval. We don't have any good explanation for the presence of the massive ramp, it seems like something that is being charged and suddenly discharges itself. We have checked that no pin is floating on the SPI interface.

We are using the internal FIFO to store and then retrieve the data every two seconds. Can you relate this issue to any known behavior of the sensor?

Thank you for your consideration.

Gustavo.

[Eleon BORLINI]

Hi Gustavo @gutzchi​ ,

Is the SPI communication ok, even if the VDDIO is dumping in that way?

How often are you reading the FIFO batches (maybe the effect you re seeing can be related to this reading phase).

-Eleon

[gutzchi]

Hi Eleon @Eleon BORLINI​ ,

The SPI communication is working perfectly.

In the photos above, I am transferring the data from the FIFO every 4 seconds.

After some additional tests, I have discovered that these ramps disappear if the controller communicates in intervals less than around 250ms.

If an event is superimposed every 200ms that reads a dummy register from the sensor along the 4 seconds FIFO read event, the power profile is as expected (the wedges illustrate the transmission interval):

However, if the frequency of the dummy event is reduced to 400ms, then the following power profile is obtained:

I hope these new photos will help.

Gustavo.

[gutzchi]

@Eleon BORLINI​ Another thing I forgot to mention is that this behavior is only encountered in the SPI interface, the I2C mode works as expected.