• State Resolved
  • Locked Locked
  • Replies 5 replies
  • Subscribers 15 subscribers
  • Views 342 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

ISOW7841: SPI SCLK issue

Yue TANG
Expert 8485 points
Part Number: ISOW7841
Other Parts Discussed in Thread: LM2775

Hi,

I'm trying to use a ISOW7841 to isolate SPI interface  between a MCU and ADC. My connection is as below, but can't get a right communication . I found if I directly connect SCLK  between MCU and ADC, and keep other lines pass through the ISOW7841. I can get a right SPI communication.  please kindly suggest what should I pay attention to ? thanks.  BTW, my spi speed is 4M, I tried to slow down to 500K, but problem is still there. 

  • 0
    TI__Genius 17100 points

    Hi Yue TANG,

    Thank you for posting to E2E! Isolator parameters of importance in this system are propagation delay and rise/fall time. Issues are not expected for SPI communication at 4MHz or 500kHz, and it will be helpful if you can provide the following waveforms on the same oscilloscope screen for analysis:

    • SCLK input to ISOW7841 and SCLK output of ISOW7841
    • MOSI input to ISOW7841 and MOSI output of ISOW7841
    • MISO input to ISOW7841 and MISO output of ISOW7841
    • SCLK and MOSI inputs to ISOW7841
    • SCLK and MOSI outputs to ISOW7841

    If SCLK and CS channels are interchanged, does this behavior continue?


    Respectfully,
    Manuel Chavez

  • 0 in reply to Manuel Chavez
    TI__Expert 8485 points

    Swapping the SCLK and CS  solved my issue. thanks. 

    BTW, if I supplied ISOW7841 with 5V and choosed 5V ISO output.  What's the signal channels voltage level?  the SPI interface at both side are 3.3V, but I have to supply the ADC side with 5V, ADC need this 5V to split to +-2.5V.  

  • 0 in reply to Yue TANG
    TI__Genius 17100 points

    Hi Yue Tang,

    You're welcome! Was there a change in software to accompany swapping SCLK and CS channels?

    ISOW7841 output signals range from 0V at LOW levels to Viso at HIGH levels. Depending on load requirements, it may be possible to boost ISOW7841's isolated output to 5V using a boost converter like LM2775.


    Please let me know your thoughts.


    Thank you,
    Manuel Chavez

  • 0 in reply to Manuel Chavez
    TI__Expert 8485 points

    I see. thanks for the reply. 

  • 0 in reply to Yue TANG
    TI__Genius 17100 points

    Yue Tang,

    You're welcome!


    Have a good day,
    Manuel Chavez