LIS3DH Module: Unexpected Power Consumption in Power-Down and Low-Power modes

[chris_]

Dear forum,

I'm actually working on LIS3DH module and I'm facing some issues according power consumption.

The board on which this module is mounted is the RAK2270 Sticker (schematics in attached files).

The module is driven by a STM32WLE5JCI6 and put in stop mode 2 with analog input for SCL and SDA lines.

I've also send the command to set the SDO_PU_DISC bit because pull-up is disconnected to SDO/SA0 pin.

First wrong behavior is the current consumption in Power-Down mode.

According AN3308 p.13 the device has to enter automatically in this mode after power-up and boot procedure (5ms)

But in this mode it still reacts and consumes power when there are activity like several shocks next to the module (see power-down_behavior.png).

As we can see on the screenshot, I can get correct value (around 2-3uA) but only during a short period after a shock (272ms on the example).

Then after this delay, the module consumes energy and reaches an average of 100uA.

After that even when I setup the Low-Power mode 8bit with ODR 10Hz with full scale selection to 2g .

I get the same wrong behavior with a good consumption just after a shock and bad consumtion after a certain delay (see low-power_behavior.png in attached files).

It would be perfect if it can be stable at 2-3uA as it is actually just after a shock detection.

Is there some specific command that needs to be send ? 

Thanks in advance for your help.

Regards,

Chris

[Federica Bossi]

Hi @chris_ ,

The current measurement can change based on where it is performed in the schematic. Could you please indicate where the measuring was done in the schematic?
The LIS3DH has been isolated from the power supply for a correct measurement. Other devices on the I2C BUS could influence the measurement.
Check the ultra low power conditions from this document

[chris_]

Hi @Federica Bossi ,

For current measurement I use the Otii Arc Pro by Qoitech and use it has Battery thru J1 connector (BAT+/BAT-). On this board there is only the LIS3DH and the MCU RAK3172 SIP module. Other modules like ECC, EEPROM,Temperature Sensor or BMX160 are not connected as you can see below :

I read the documentation, but it doesn't explain me why I'm having a link between current consumption and shock even when I put in in Power-Down mode (0x00 to ODR values in LIS3DH_CTRL_REG1).

And also why there is this good current consumption only after a shock detection.

Thank you again in advance. 

 

[Federica Bossi]

Hi @chris_ ,

To exclude any other phenomenon, it is necessary to have the current measurement of the individual lis3dh device.
try to cut the power line (VDD and VDDio together) and measure the current at the cut point. This way we will have the consumption of the individual lis3dh without MCU to better evaluate the phenomenon.

[chris_]

Hi @Federica Bossi

Ok to do this much easier I purschased the evalboard Adafruit LIS3DH.

I'll keep you in touch once received and tested.

[chris_]

Hi @Federica Bossi ,

So I've just received and tested the Adafruit LIS3DH.

The behavior is much better but when I setup the power-down mode, the consumption profile still has some very small reactions to shocks as you can below, nothing compared to the other board by the way.

Also I've taken another RAK2270 board in order to compare. It also reacts, more than on the Adafruit but less than the first board.

On the screenshot below we can see in pink the consumption in power-down with a ground consumption of around 75uA (3v3 regulator, ...).
In blue, the LP_Mode with ODR set at 10Hz. As expected this mode adds around 5uA and the acquisition period is 100ms.

On RAK2270 boards I use the same commands as on the Adafruit, and as I said previously, there are only two elements, the MCU and the LIS3DH module.

Based on your experience, what can make the module reacting to shocks even when I send the power-down command ?

Could the difference in behavior between the cards also be due to module quality or degradation level ?

Thanks in advance.