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ISO1540: The output puts up a wrong level

David Chance
Genius 4785 points

Part Number: ISO1540

I use ISO1540 (see original discussion on ), but the data is wrong after the isolation

This is from the slave side, and the signal looks good (there is a tiny step near the right side of the screen, but it will not be mistaken as logic 1)

This is from the master side, and the tiny step is now a big step there, over 0.8V, and the 3.3V micro can easily read it as 1

Any pointer for resolve this?

Thanks!

  • 0
    TI__Genius 17100 points
    Hi David!

    Thank you for continuing to work with the ISO1540. Can you please share a schematic of this system including passives connected to ISO1540 and the points each oscilloscope capture measured?

    What are your output current loads? If current drawn from the device is outside of certain values this can affect the size of "step" voltages. Otherwise, I'd like to check if 3.3V (micro-controller side) is Vcc2 side and 5V (slave side) is Vcc1 side or vice versa.


    Thank you for posting to E2E! Happy New Year,

    Manuel Chavez
  • 0 in reply to Manuel Chavez
    Genius 4785 points

    Here is the schematic:

    the waveform was taken at ISO1540, 2 is the left side,  1 is the right side

    The SDA and SCL on the left side goes TM4C1294's I2C2 port

  • 0 in reply to David Chance
    TI__Guru 57515 points
    Hi David,

    Thanks for sharing the schematic, it looks good to me.
    May be your question is already answered in other couple E2E posts, please have a look at the below E2E posts.

    e2e.ti.com/.../733012
    e2e.ti.com/.../747051

    If you feel the above posts didn't answer your question, please feel free let us know. Thanks.


    Regards,
    Koteshwar Rao