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ISO7741: About the immunity to noise superposed on digital signals

Part Number: ISO7741

Hello support team,

I have some questions about ISO7741 and ISO7341.
Could you teach me about the immunity to noise superposed on digital signals for these devices.
Does the immunity depend on frequency and pulse width of the noise?
If it depends, how much frequency and pulse width will be malfunction?
How much frequency and pulse width will these devices malfunction?

Best regards,
M. Tachibana

  • Hi Masanori san,

    Could you please clarify the noise seen by the device? From your description it looks like the noise is a differential noise applied between input pin with respect to the same side ground. (Example noise exists between INA and GND1)

    If above is scenario is the case,
    1) ISO7741 is a very high speed device (100Mbps). These devices may even reproduce any glitches that are as low as 2ns. If any glitches having a pulse width higher than 1 ns needs to be filtered, then an external RC filter should be placed at the input.

    2) ISO7341 is a relatively lower speed device (25Mbps). There is a glitch suppression integrated which has a typical value of 20ns at 5V operation. Any glitches with pulse width lower than this value will be suppressed. Please refer to Figure 12 in datasheet to see variation of Glitch suppression time with temperature.

    If on the other hand, the noise is a common mode noise which occurs across the isolation barrier or if the noise is related to an electro-magnetic event like radiated immunity. The ISO7741 architecture is designed to be much more robust than ISO7341 for such kind of noises.

    Please confirm the nature of noise seen on the system. Let me know if any additional details are required.

    Regards,
    Anand Reghunathan
  • In reply to Anand Reghunathan:

    Hello Anand-san,

    Thank you for your information and advice.

    Our customer would like to confirm the difference with the photo-couplers in the noise pulse test.
    The customer is concerned about whether noise is misrecognized as data. So I guess he would like to know is rather glitch immunity than noise immunity.

    Best regards,
    M. Tachibana
  • In reply to Masanori Tachibana:

    Hi Masanori san,

    Could you please give me more details on the noise immunity test being performed? I would require this data to better comment on your question.
    Thanks.

    Regards,
    Anand Reghunathan