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AB.4
AB.4
Associate III
July 13, 2020
Question

Set LIS2DH12 in power down mode

Hello ST Community,

My application involves nRF52 series processor which interfaces with LIS2DH12 via SPI and I am trying to reduce the power consumption as much as possible when the processor is in sleep mode.

I understand that, as soon as power is applied, the sensor is in power-down mode. In this mode (i.e no SPI commands sent to the sensor), the total power consumption is ~ 6 uA with the processor in sleep mode.

Now, the processor can wake up or go to sleep mode when certain commands are received via NFC.

I am using LIS2DH12 to generate interrupts for impact , freefall and wakeup and so, I configure the sensor with register values as follows:

CTRL1_REG - 0x37

CTRL3_REG - 0x40

CTRL4_REG - 0x88

CTRL5_REG - 0x0A

CTRL6_REG - 0x28

INT1_THS - 0x0B

INT1_DUR - 0x0A

INT1_CFG - 0x95

INT2_THS - 0x4E

INT2_DUR - 0x01

INT2_CFG - 0x2A

ACT_THS - 0x05

ACT_DUR - 0x20

When the command to wake up is given, the sensor LIS2DH12 is configured as shown above and the functionality is as expected. In this case, the power consumption is ~ 12 uA. Now, if the command to sleep is given again, I want to minimise power consumption and so, I send the command to put the LIS2DH12 in power down mode as follows before putting the processor to sleep:

Read REFERENCE Register (0x26)

Write value 0x00 to CTRL1_REG

However, in this case, the power consumption is at 8 uA even though the power-down command was sent. I also confirmed that this extra 2 uA is from LIS2DH12 by not initialising the sensor at all. In this case, on power up, power consumption is 6 uA and when the command to sleep is given after it is woken up, it goes back to 6 uA.

Could you please let me know if I am following the right process to set the sensor in power-down mode?

Thanks in advance.

Regards,

Anusha

    This topic has been closed for replies.

    2 replies

    Eleon BORLINI
    Eleon BORLINI
    ST Employee
    July 13, 2020

    Hi @AB.4​ , the procedure of reading REFERENCE Register and setting 0x00 to CTRL1_REG should be the correct one to enter power-down mode... Btw, which Vdd level are you using? 1.8V or higher? And are the SPI lines left open-drain during PD mode? If you are sure this is not a nRF52 application processor issue, I suggest you to check the LIS2DH12 C drivers on Github repository, if they can be of any help for you. Regards

    AB.4
    AB.4Author
    Associate III
    July 14, 2020

    Hi Eleon,

    Thanks for your response.

    1. We're using 3 V as Vdd.
    2. Yes, during PD mode, the SPI lines are returned to the default state.
    3. I checked out the Github repository and the only function that I see for operating mode is lis2dh12_operating_mode_set which sets low-power or normal mode based on the resolution.

    I came across this note in the datasheet regarding 'Sleep-to-wake and Return-to-sleep' which mentions that when the acceleration goes below threshold value, ODR[3:0] are not considered (Page 18, section 3.2.4 in https://www.st.com/resource/en/datasheet/lis2dh12.pdf). In my setup, I am using the register ACT_THS. The power-down mode is enabled in the sensor by writing to CTRL1_REG when the device acceleration is already below the threshold in ACT_THS. So, if the sensor's acceleration is below ACT_THS value and power-down mode is enabled, will it still remain in low-power mode only?

    Regards,

    Anusha

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