Challenges with LPS22DF: VDD_IO and VDD Interaction Causing I²C Issues

[Adi_Aljarbou]

Hi,

We are working with the LPS22DF pressure sensor to be used in our device adapting a 3.3V system and have encountered issues related to the interaction between VDD_IO, VDD, and the I²C bus.

• When VDD_IO and VDD are connected to the same 3.3V supply:
  • The I²C bus behaves as expected. (No issues here)
    
    
    
• However, when we disconnect VDD_IO and VDD, while I2C is active to be used for other sensors to communicate, the sensor seems to backfeed through VDD_IO's internal pull-up to VDD, interfering with the I²C bus (e.g., pulling lines to ~1.5–1.6V). (this is our theory at least)
  
  

• When VDD_IO is powered but VDD is not:

  • I²C communication is disrupted.
  • The sensor seems to partially power itself through internal pull-ups, potentially backfeeding into VDD.
    
    
• In addition, CS pin will sometimes influence the I2C bus if its connected to HIGH.
  
  

We have tested it using the evaluation kit and also on a breadboard. What we did was add a diode between VDD and VDD_IO to temporarily eliminate the issue. However, the I²C lines are still not stable and show a "wavy" signal.

Do you have any suggestions or recommendations? This is the first time we have encountered this kind of behavior with an ST sensor. We do not want to use power-down mode, as we are required to maintain extremely low current consumption. Using a different power source is also not an option.