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ISO1541: Questions

Allan Fan
Expert 5740 points
Part Number: ISO1541

Hi Expert,

Customer used ISO1541 and when doing measurement, they saw from host side SDA1 always a spike though it doesn't cause any communication error. Do you have comments or concern about it? 

CH1: SDA1 ; CH3: SDA2

CH1: SCL1; CH3: SCL2

Regards,

Allan

  • 0
    TI__Genius 17100 points

    Hi Allan,

    Thank you for posting to E2E! The waveforms in the images are labeled as SCL1 and SCL2, but the text mentions the spike appears on SDA1: does the spike appear on only SCL1 or SDA1? or does it appear on both?

    From the images, it seems like the spike on SCL1 appears due to coupling from SCL2. If this is the case, our customer could try reducing the 10k pull-up resistors to a lower value. There's a chance the coupling is occurring from SCL1 to SCL2, so to confirm please let us know which pull-up resistor values are used on the host side and how the ISO1541 I2C signals are routed. If this information is to be kept private, feel free to send me a Personal Message.


    Thank you,
    Manuel Chavez

  • 0 in reply to Manuel Chavez
    Prodigy 60 points

    Hi Manuel Chavez

    The spike only appear on SCL1.
    The pull-up resistor on SCL1 is 1.5K not 10K, so should I make it smaller?

    Regards,

    Louisa

  • 0 in reply to Louisa Lin
    TI__Genius 17100 points

    Hi Louisa,

    Thank you for clarifying this information. Since the pull-up resistance on SCL1 is already low, we will try to figure out whether this spike is due to device behavior or a different external cause like coupling from the PCB traces. At which ambient temperature is this system being tested?

    Please allow me 1-2 days to replicate this use case in our lab and make recommendations based on the data.


    Thank you,
    Manuel Chavez

  • 0 in reply to Manuel Chavez
    Prodigy 60 points

    Hi Manuel Chavez

    The test environment temperature is about 25 degrees.
    Please let me know if there is any new development.

    Thank you,

    Louisa Lin

  • 0 in reply to Louisa Lin
    TI__Genius 17100 points

    Hi Louisa,

    Thank you for confirming -- I will keep you updated!


    Respectfully,
    Manuel Chavez

  • 0 in reply to Manuel Chavez
    TI__Expert 5740 points

    Hi Manuel,

    Sorry about the typo, I also have clarified with Louisa that the spike was happened on SDA1 NOT SCL1. 

    Some more information, the host i2c connects to four devices, customer remove one by one and confirmed the spike would gone by removing iso1541. Please let us know if further comments.

    Thanks,

    Allan  

  • 0 in reply to Allan Fan
    TI__Genius 17100 points

    Hi Louisa, Allan,

    Thank you for this additional information. Below are SDA1 and SDA2 waveforms we captured in a similar configuration as you've described:



    We were not able to replicate this spike in our setup, and although there is some noise coupling in the image, it is not from the ISO1541 and can be ignored. The spike you see could be appearing due to coupling from nearby PCB traces or another device trying to drive the bus, but in either case, there shouldn't be any issues caused by the spike for the device or system.

    Please let us know if you have any additional questions.


    Thank you,
    Manuel Chavez