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ISO3086T: ESD Claims in datasheet

Part Number: ISO3086T

To whom it may concern,

I was interested in using this part on a current design, but I'm concerned by the following excerpt from the datasheet:

"TI recommends not testing equipment transient susceptibility with ESD generators or consider product claims of

ESD ratings above the barrier transient ratings of an isolated interface. ESD is best managed through recessing

or covering connector pins in a conductive connector shell and installer training."

 

I am confused by this statement given the ESD claims of +/-11kV in the datasheet.

Would it be possible to confirm if this part meets the following:

- EN 61000-4 level 3 air discharge (+/-8kV)

- EN 61000-4 level 2 contact discharge (+/-4kV)

Look forward to your response.

Many Thanks,

Bhav

  • Hi Bhav,

    Let me try to give more clarity here.

    The ESD claim of 11kV in the datasheet is HBM-ESD rating where the stress is applied between the RS-485 bus pins with respect to GND2 (Same side Ground as the RS-485). This has been tested and claimed in the datasheet.

    The statement in the datasheet suggests that the end equipment be shielded from ESD type events using various methods to help improve the ESD rating of the final system. This is directly related to the example given in datasheet above the statement where it shows that the if designed properly the full transient waveform will come across the ISO barrier and protect all the other components from getting damaged. But if the transient voltage exceeds the ratings of the isolator it could end up damaging the isolator. This testing will very heavily depend on the design/layout and components present on the final system/end equipment. (Note that this is an Across the barrier test where the reference is GND1 unlike the 11kV HBM where the reference was GND2).

    I understand you are looking at the EN/IEC ESD standards. As i had mentioned earlier, this is a system level standard test and will very heavily depend on the way the end equipment is designed. Could you please help me out by giving a bit more clarity on the way the testing is intended to be done? For the EN 61000-4 tests I am assuming that the strike point is on the RS-485 bus lines. Where is the reference point (Protective Earth) connected in the end equipment? Is it on GND2 or GND1?

    I hope I was able to answer some of your questions with this response. Let me know if any additional clarity is required on any of the explanations.

    Regards,
    Anand Reghunathan

  • In reply to Anand Reghunathan:

    Hi Anand,

    Thanks for your informative response.

    The testing will be done as described in the TI application note:

    http://www.ti.com/lit/an/slva711/slva711.pdf

    We would be implementing this part as per the ISO3086T application circuit and performing the ESD tests as described in the above note to the external bus terminals.  In this instance, I would presume the internal ESD protection be referenced to VCC2 and GND2 and shunt away these transients and protect the barrier from these higher voltages?

    Using the application circuit for the ISO3086T, will it pass the following levels:

    - EN 61000-4 level 3 air discharge (+/-8kV)

    - EN 61000-4 level 2 contact discharge (+/-4kV)

    Look forward to your response.

    Many Thanks,

    Bhav

  • In reply to Bhavesh Tailor:

    Hi Anand,

    Just wondering if you had chance to look at my last post?

    Look forward to your response.

    Many Thanks,

    Bhav

    Bhavesh Tailor

    Hi Anand,

    Thanks for your informative response.

    The testing will be done as described in the TI application note:

    http://www.ti.com/lit/an/slva711/slva711.pdf

    We would be implementing this part as per the ISO3086T application circuit and performing the ESD tests as described in the above note to the external bus terminals.  In this instance, I would presume the internal ESD protection be referenced to VCC2 and GND2 and shunt away these transients and protect the barrier from these higher voltages?

    Using the application circuit for the ISO3086T, will it pass the following levels:

    - EN 61000-4 level 3 air discharge (+/-8kV)

    - EN 61000-4 level 2 contact discharge (+/-4kV)

    Look forward to your response.

    Many Thanks,

    Bhav

  • In reply to Bhavesh Tailor:

    Hi Bhav,

    Sorry for the delayed response. I was checking this data with the team internally.
    It looks like the 4kV is the borderline capability of the internal protection of the device and it will depend a lot on the way the system is designed.

    If we have protection components on the bus lines (like TVS) the system should be capable of passing higher levels. Choosing a TVS with high peak pulse power dissipation and peak impulse current will determine the discharge capability and electrostatic discharge (ESD) level in a system. I would recommend having these bus protection components in place if the system if these levels are targeted.

    Regards,
    Anand Reghunathan
  • In reply to Anand Reghunathan:

    Hi Anand,

    Thanks for chasing this.

    Could you depict exactly how the system was implemented to achieve the +/-11kV ?

    We would hope to use this device as implemented in the application and it fits into the system as depicted below:

    In this implementation, would we expect to damage the isolation barrier, or would the +/-11kV protection apply here?

    Further to this enquiry, could you also confirm the maximum output power of the ISO3086T-EVM-436 isolated supply?

    Look forward to your response.

    Many Thanks,

    Bhav

  • In reply to Bhavesh Tailor:

    Apologies it seem the picture got missed off when I posted.  Please see below:

  • In reply to Bhavesh Tailor:

    Hi Bhav,

    The 11kV HBM test that was quoted in datasheet is a different kind of ESD test than the IEC/EN ESD you are looking to test.
    The HBM test is an unpowered test and the stress was directly applied on the device pins (no protection components). But the HBM results cannot be correlated to a pass level in the EN 61000-4 ESD. So the 11kV number will not apply in the EN ESD testing.

    According to your previous explanation regarding the test methodology, I understood that the ESD strike will be done with reference to GND2 and not with respect to GND1. This is very important as it will determine which part of the device is going to be stressed in the ESD strike.

    As mentioned earlier, if it is with respect to GND2, the isolation barrier will not come into the picture. This is called a "Same-Side ESD test". The stress voltage will be on the internal ESD protection capability on the RS-485 pins of the device. For this kind of testing the device/system capability can be further improved by adding extra protection components like the TVS on the bus lines.

    Even if the stress voltage exceeds the device capability for the Same Side ESD test, the damage will be mostly on the RS-485 section of the device and the isolation barrier should remain intact.

    Regards,
    Anand Reghunathan