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ISO1540: Questions

Allan Fan
Expert 6710 points
Part Number: ISO1540
Other Parts Discussed in Thread: ISO1640

Hi expert,

Customer used ISO1540 for i2c and in order to verify the part can support bi-direction, they did two tests;

case1: side1 connects to PSE_I2C, side2 connects to MCU_I2C

case2: side1 connects to MCU_I2C, side2 connects to PSE_I2C

To be clear, there is no communication issue.

Could you please explain why the low level are different and the time period of low level are different as well? 

Regards,

Allan 

  • 0
    TI__Expert 8030 points

    Hi Allan,

    Thanks for reaching out. 

    The behavior that you are observing for the ISO1540 is expected. To achieve bidirectionality on the channels, the ISO1540 will have a different low level voltage value depending on the direction that data is being sent (a more in-depth explanation on why this is the case is explained in this E2E post here). When working as an output, the side 1 channels will produce a low-level voltage of around 0.8 V, but when working as an input the side 1 channels will see a lower voltage. The exact range of low-level output voltage (VOL) values that will be observed on the channels of this device can be found in the "6.9 - Electrical Characteristics" section of the datasheet.  

    In addition, I would also like to point out that side 1 of the device should only be connected to 1 node, and not to multiple nodes on an I2C bus. Side 2 is the only side of the device that can be connected to multiple I2C nodes. Please ensure that this is the case in your circuit.

    I did not see any time differences in the waveform screenshots that you included with your post. If you would like me to examine a specific location of the waveform where there are time differences, please let me know.

    I also noticed that you are using the ISO1540 for this application. For improved performance, we recommend using the ISO1640.

    Please let me know if you have any further questions.

    Regards,

    Kenneth