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CMehr.1
Visitor II
June 19, 2022
Question

LSM6DSM VDD and VDDIO Usage

  • June 19, 2022
  • 2 replies
  • 1832 views

Hello,

In my prospective application, I am trying to use the LSM6DSM and also achieve a very low power state.

In my application, the host device will operate at 3.3V. The LSM6DSM could be supplied by 1.8V so that it draws the least power, see here: https://community.st.com/s/question/0D53W00001bks5vSAA/lsm6dsm-power-draw-at-different-voltages

I would like the LSM6DSM to operate in "pedometer mode". I will retrieve this pedometer value infrequently. Is it possible to turn off the VDD_IO 3.3V supply, while maintaining the VDD 1.8V supply, so that the LSM6DSM sensing element can continue in the "pedometer mode"? And when I would like to retrieve the pedometer value, I can turn on the VDD_IO supply to 3.3V, retrieve the value, and then once again turn off VDD_IO?

The purpose of turning off the 3.3V VDD_IO is to reduce power as much as possible. If this isn't the recommended path, please let me know. Essentially, there are perhaps these statements to be verified:

  1. I can power VDD_IO with 3.3V and VDD with 1.8V, so that the LSM6DSM operates in lowest power mode and the host processor can communicate with the LSM6DSM over a 3.3V physical layer
  2. I can remove power from VDD_IO, and the sensing element in the LSM6DSM will continue operating as configured
  3. I can reapply power to VDD_IO, and retrieve sensing element readings
  4. Removing VDD_IO will drive the LSM6DSM into the lowest power state while maintaining the sensing configuration
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    2 replies

    E
    Eleon BORLINI
    ST Employee
    June 24, 2022

    Hi @CMehr.1​ ,

    unfortunately our general suggestion is to use the VddIO equal or less than the Vdd. You might try to reduce the ODR, to decrease the power consumption. However, feel free to try also your procedure, but we cannot guarantee this is a safe flow.

    -Eleon

    C
    CMehr.1Author
    Visitor II
    June 27, 2022

    Eleon,

    Is there a reason for the general suggestion being vddIO equal or less than Vdd? Viewing the datasheet, I'm led to believe that vddIO can be greater than Vdd. VddIO is generally referenced as "Power supply for I/O pins"

    Cole

    E
    Eleon BORLINI
    ST Employee
    June 27, 2022

    Hi Cole @CMehr.1​ ,

    in principles they could be managed independently, but the Vdd is the level that references all the ASIC analog front end (together with the voltage and current references), while the Vdd IO is the reference for the digital communication.

    So, it would be better if they were aligned.

    But this doesn't prevent you to make a check on your system.

    -Eleon

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