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ISO7741: RF susceptibility of the ISO7741FDW

Warren
Prodigy 20 points

Part Number: ISO7741
Other Parts Discussed in Thread: ISO6441

We discovered that the ISO7741FDW is susuceptable to radiated fileds at 1.2GHz and 2.4GHz. A signficant amount of effort was put into tightening the shielding of the electronics encloser and filtering all I/O, but we have not been able to reliably solve the issue. We replaced the isolator with the equivilent Skyworks isolator and have had reliably passing results with no upsets. We would like to know if there are known susceptabilies with the ISO7741FDW. My best guess is that the carrier used for signal transmission must be close to 1.2GHz, and the threat is jamming the transmitted signal. There is an advertised new replacement part on TI's web site, the ISO6441. This is advertised as "EMI robust". Would this part have a better chance of passing radiated susceptability testing?

  • 0
    TI__Mastermind 21916 points

    Hi Warren,

    Thanks for reaching out.

    Can you please provide more information about the testing that the customer performed?

    1. What is the radiated test standard that customer is performing? 
    2. When you say susceptibility, can you please describe the failure observed?
      1. If the device had applied signal during the test, please provide waveforms. 
    3. Can you also please describe the preventative solutions that the customer has already tried?
      1. typically, a y-cap is suggested to place between GND1 and GND2 to reduce noise (<100pF)
    4. Can you please describe the customer system? Since you mentioned 1.2-2.4GHz, is this an application that has a wireless communication?
      1. https://www.ti.com/lit/an/slyt742/slyt742.pdf?ts=1772173734801&ref_url=https%253A%252F%252Fwww.google.com%252F

    Regards,
    Aaditya

  • 0
    Prodigy 20 points

    Aaditya,

    We performed the testing as part of the product qualification. We get a fault indication from the isolator and the GaN FET combination. I.e., the output of the isolator is toggling high when it shouldn't. This isolator is being used in combination with TI's GaN (as recommended in application notes), so an upset in the isolator will cause the power device to turn on when it shouldn't, resulting is a short circuit fault. This has been difficult to troubleshoot since you can't add leads to a part when the unit is in the EMI chamber. Our breakthrough came when we replaced the isolator with a Skyworks equivalent part and the susceptibility was no longer present. We wouldn't normally place a 100pF capacitor across the isolator, as this would load the switch node in the converter and cause noise to be coupled to the control ground. The RF qualification frequency range represents radio communications and exposure to radar pulses.

    I have historically experienced magnetic field and narrow pulse width upsets with TI's isolators. There are indications that this generation of digital isolators is less prone to upset because of design improvements. However, it appears that there may still be some susceptibility.

  • 0 in reply to Warren
    Prodigy 20 points

    We've been working on this problem and trying to make contact with TI engineering through the FAE for over a month. I can't go any deeper on details over a public forum, but I'd like to better understand the issue at the component level and if there are improvements being made in later releases, like the ISO6641 mentioned above.

  • 0 in reply to Warren
    TI__Mastermind 21916 points

    Hi Warren, 

    I understand that you have been trying to contact us. If its easier to share more information, please find my email on my profile and directly contact me through email. I'd be happy to also support a call so we can fully understand what is happening and formulate the next steps.

    In terms of the ISO6441, this device may be a good consideration for you. This device is our newest generation of digital isolators and supports up to 150Mbps: https://www.ti.com/product/ISO6441. Since the architecture and design is newer and different, this may allow for your system to function in the given setup. Either way, optimizing the system design for reduced RF on the isolator will be helpful.

    Regards,
    Aaditya