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I am working with an ESP8266 and an ICM-20948 IMU chip. According to the datasheet, the IMU chip works on up to 3.6V VDD, but I/O voltage only goes up to 1.95V.

I thought about using resistors for stepping down 3.3V->1.8V for one way. However the ESP only recognizes a HIGH voltage level after 2.5V, so I cannot directly connect the other way and I need some sort of level shifter.

The connection is a 400 kHz I²C bus. I've heard that at this frequency, resistors should not be used for level shifting. Is this true, should I rather use a 1.8V regulator, and MOSFETs for the level shifting? The final PCB will be in a small handheld device, so I want to keep component count low for a small footprint.

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  • \$\begingroup\$ The ESP8266 is a 3.3V microcontroller with 3.3V I/O. I wonder why you are seeing only 1.95V on its I/O. \$\endgroup\$
    – ocrdu
    Sep 22, 2020 at 8:50
  • \$\begingroup\$ @ocrdu The 1.95V I/O is the maximum IO voltage for the IMU chip according to the datasheet, not for the ESP. \$\endgroup\$
    – Twometer
    Sep 22, 2020 at 8:52

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For I2C bus level translation, you can't simply use resistors. You need a FET based translator or a chip that basically does the same, to allow translation between 3.3V and 1.8V devices, and pull-ups on each side to the respective supplies. You also need a 1.8V regulator to power the 1.8V VDDIO. You might as well use the 1.8V for the VDD too. Regulator can be powered from 3.3V.

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