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ISO1430: Input Hysteresis 30mV

Brian Wang0928
Genius 14280 points
Part Number: ISO1430


The input hysteresis is 30mV for ISO1430. Customer think the lower hysteresis has lower noise immunity as ESD, Surge, EFT...etc. Competition is about 70mV. 

Do we see any problem with lower input hysteresis for EMC test? Or any product has higher input hysteresis? 

Regards

Brian W

  • 0
    TI__Guru 55825 points

    Hi Brian,

    Most of the noise in the system is usually common-mode and hence it may not directly impact the differential voltage on RS-485 bus. ISO1430 already supports very good EMC performance and hence you shouldn't see any issues.
    Lower hysteresis would mean that the device can work with even the lowest of input signal swing, this means it can support longer communication cables. Thanks.

    Regards,
    Koteshwar Rao

  • 0 in reply to Koteshwar Rao
    TI__Genius 14280 points

    Hello Rao,

    Very Thanks. Customer said when the RS485 cable is suffered with noise tests as ESD/EFT/Surge. The lower hysteresis in the RS485 could lead to the fault trigger problem and more sensitive to noises since RD usually puts TVS/ESD diodes on the A and B bus of the RS485 and the tolerance of the TVS/ESD diode could cause the differential voltage during testing. It is RD's experience. Do you agree with this one?

    And also, why we defined lower hysteresis for 30mV,typ only, not higher? Any reason? Or any benefit with higher hysteresis?

    Regards

    Brian W 

  • 0 in reply to Brian Wang0928
    TI__Guru 55825 points

    Hi Brian,

    This is concern for single-ended signals and not the case for differential signals. Most of the external noises including ESD, EFT and Surge are common-mode and hence, they do not affect the voltage swing between A & B instead this noise rides on both the lines as a common-mode noise. The immunity to such noise depends on the internal design of transceiver and ISO1430 has very good immunity against such noises.

    From the datasheet, you can see that the device supports 16kV IEC ESD and 4kV EFT without any need for external components like TVS diodes or common-mode chokes. Customer can refer these guaranteed performance parameters to understand how good the device is. The hysteresis doesn't play a direct role in these performances.

    Lower hysteresis offers longer range and higher hysteresis creates a larger unknown region. Hence, I believe 30mV of hysteresis is a sweet spot for optimal performance. Let me know if you have any other questions, thank you.

    Regards,
    Koteshwar Rao