• State TI Thinks Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 2 answers
  • Subscribers 14 subscribers
  • Views 683 views
  • Users 0 members are here
Support feedback
Options
Options
Related

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.

ISO7741: Unable to read SPI data

Cashewmiro
Prodigy 30 points

Part Number: ISO7741

Hello TI team.

I am using iso7741 as an isolator between the uC and external ADC to read analog data. The external ADC being used is AD7887 from analog devices. I am using 2 of these combos to read data from 2 seperate interfaces. I am currently facing an issue where I'm unable to read the data. I am getting continous high signal in my MISO line. Is ISO7741 not suitable for the application?

image.png

  • 0
    TI__Mastermind 34580 points

    Hello Cashewmiro, 

    Thank you for reaching out. I do not see an issue with your schematic. The ISO7741 is a good device to isolate the data signal. 

    • What is the data rate and SCLK frequency of the application?
    • Does the AD7887 transmit signal correctly with the isolator removed (or ISO7741 pin 11 disconnected)? 

    Best,
    Andrew

  • 0
    Prodigy 30 points

    CLK frequency is 1MHz. The issue is found in ISO7741 as we need a dedicated level shifter it is OK without isolation as well. Is there any dedicated level shifters that we can use instead of iso7741 in same package. The issue is found that the iso7741 is pulling the data lines high. Using a dedicated level shifter instead of an isolator may solve the issue. Can you suggest any spi compatible level shifters in same package.

  • 0 in reply to Cashewmiro
    TI__Mastermind 34580 points

    Hello Cashewmiro, 

    TI has many voltage-level translators. Please see Voltage translators product selection | TI.com for further options (TXB0104) looks to be a good place to start.

    That being said, if the issue is that ISO7741 is pulling lines high this should be an easy fix. ISO7741 should not do this unless the ENx line is in the disabled state or one of the VCCx is powered down. 

    If the outputs are enabled and the isolator is powered the output should always match the input. You can also try using ISO7741F which has default low outputs ([FAQ] What is the difference between ISOxxxxF and ISOxxxx devices (Ex. ISO7741 vs. ISO7741F)?)

    Best,
    Andrew