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ISO1540: please suggest the ISO1540 I2C level fail

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Replies: 12

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Part Number: ISO1540

Sir,.

do you suggest the ISO1540 I2C level fail please, thanks

  • In reply to PHILIP HSU:

    Hi Philip,

    I am not sure if I understand your question correctly. Are you asking why there is about 0.8V on the yellow waveform when the blue one is 0V? If this is your question then please read below the FAQ E2E post. This is expected and normal, it doesn't cause any issue in communication providing the I2C isolator is interfaced to the compatible I/Os on MCU or ADC. Please do go through the post and let us know if you have any questions, thank you.

    Regards,
    Koteshwar Rao

  • In reply to Koteshwar Rao:

    Hi Rao,.

    Actually, it was failed in I2C communication as waveform as shown,.

    do you suspect the placement issue of the GND via between isolator ?

  • In reply to PHILIP HSU:

    Hi Philip,

    I do not think the GND via is causing any issue here. If customer is seeing a communication issue, it could be due to mismatch in I/O logic levels between ISO1540 Side1 & MCU.

    Could you please share MCU I2C pins VIL, VIH & VOL levels? Alternatively you could also share the MCU part number and mention which pins are configured as I2C and interfaced to ISO1540 Side1. Thanks.

    Regards,
    Koteshwar Rao

  • In reply to Koteshwar Rao:

    Hi Philip,

    Please do share MCU I2C pins VIL, VIH & VOL levels? Alternatively you could also share the MCU part number and mention which pins are configured as I2C and interfaced to ISO1540 Side1. This helps me check if there is any compatibility issue between the two devices, thanks.

    Regards,
    Koteshwar Rao

  • In reply to Koteshwar Rao:

    Yes RAO,.

    the controller is STM32F030CC and please refer tp the attachment for ISO1540 side, thanks

    thanks for your suggestion,.

    st mcu_bd v12-20190815n.pdf

  • In reply to PHILIP HSU:

    Hi Philip,

    Thanks for sharing the schematic and MCU part number. I checked the I/O specifications of MCU and I see that the I/Os are compatible to ISO1540 with good margin. Hence there is no compatibility issue between MCU and ISO1540.

    I also reviewed the schematic and PCB layout again and I do not see any major concerns. Could you please confirm if the capacitors C30 & C31 that are connected to SDA1 & SCL1 are populated or not populated during the test? I see these caps are only 10pF in value, any higher values could lead to communication issue.

    Apart from what is discussed above, I do not see any major concerns. Could you please describe more details about the customer issue?

    1. When does communication fail occur?
    2. During the time when fail happens, does customer do any other EMC tests like IEC ESD?
    3. How often does this fail happen?
    4. Does this issue occur only on one board or does it happen on multiple boards?
    5. Does the issue go away when a new sample is used?

    Please do help me with above information to further debug the issue. Thanks.

    Regards,
    Koteshwar Rao

  • In reply to Koteshwar Rao:

    Hi Philip,

    Please do help us with the above requested information to be able to debug this issue, thanks.

    Regards,
    Koteshwar Rao

  • In reply to Koteshwar Rao:

    1. When does communication fail occur?   the fail situation occur always when through ISO1540  
    2. During the time when fail happens, does customer do any other EMC tests like IEC ESD? NO, never EMC testing 
    3. How often does this fail happen? it failed in the board always  
    4. Does this issue occur only on one board or does it happen on multiple boards? it happened on multiple boards of the placement
    5. Does the issue go away when a new sample is used?  NO, has changed new sample , fail symptom is here still

  • In reply to PHILIP HSU:

    Hi Philip,

    Thanks for your inputs, this is useful.

    From your response, I understand that the ISO1540 communication error occurs even under normal operating conditions and the error is continuously occurring. Since the schematic and PCB layout look fine, we do not expect such a communication error. I am not quite sure if there are any issues on the board that are not reflecting in schematic or PCB layout.

    As an experiment, could you please add a decoupling capacitor of 0.1µF very close to VCC1/GND1 and VCC2/GND2 pins? Customer may have solder these two capacitors close to the pins even though there are no footprints for these capacitors. Please do request customer to do this test.

    In addition, could you please ask customer to transmit data from side1 to side2 and capture both SDA & SCL waveform in one plot (total 4 channels, SDA1, SCL1, SDA2, SCL2)? Similarly, now transmit data from side2 to side1 (opposite of what I described in my last sentence) and capture all SDA & SCL waveform? This will help us know if the device is producing any errors or if it is transmitting correct data. This will also help us know if the issue is indeed ISO1540 related of if there is any external software issue.

    Sorry for asking so many questions and for experiments, this is necessary for me to understand customer application better and debug the issue especially because the issue is not very evident. Thanks.

    Regards,
    Koteshwar Rao

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