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P82B715: P82B715DR - I2C Expander - Different voltage on I2C lines

Part Number: P82B715

Hi,

We are using P82B715DR I2C expander for connecting to an external I2C sensor. We also have an internal I2C sensor (accelerometer) connected as in the attached schematic.
Note that both MCU and I2C expander is powered by 3.3V

Case-1:

When no external I2C sensor is connected, the I2C lines are at 1.8V. I expect it should be at 3.3V. Not sure why it is at 1.8V.
Because of this voltage issue, we see the I2C communication with an internal accelerometer is not working.

Case-2:
Once an external I2C sensor board is connected, the I2C lines are jumped to 2.1V or 2.2V. This makes the I2C communication between MCU and an internal accelerometer working as expected.

What is the reason for voltage drop?

  • Hi All,

    Changed the pull-up resistors on Lx, Ly from 4.7Kohm to 332 ohm and it improved the voltage from 1.8V to 2.3V which makes the internal accelerometer to work as expected
    However the I2C interface with an external sensor board is not working.
    Note that an external sensor board has a similiar I2C expander circuit P82B715DR.

    How to make I2C bus interface voltage to 3.3V?                                                                                                              

  • Something must be pulling the lines down. Check for wrong connections or solder bridges.

  • Hi Vel,

    Are you driving the accelerometer with the Lx Ly buffered lines? 

    Regards,

    Tyler