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Original question:

ISO3088: ESD, EFT and surge protection of RS-485 isolated node with no protective earth connection

ISO3088: ISO3088

Kumaresan N
Prodigy 10 points
Part Number: ISO3088
Other Parts Discussed in Thread: ESDS552, LMR16030, TSD05C

Tool/software:

HI Dan kisling

i have a question for you.

As you said adding one more TVS to the line will helps to conduct the High current surge( considering 1KV 42Ohm/ 23A since SM712 has 19A(8/20uA)).is it good to have varistor instead which capable of withstand 23A or more?

also i can see Line to line and line to GND in surge test procedures should we need a varistor across A to B, A to GND and B GND?

in a above picture they saying Earth reference is that Earth or Local GND (GND2 for the case ISO3088) 

  • 0
    TI__Mastermind 29285 points

    Hello Kumaresan, 

    Thank you for reaching out. If you are referencing an older thread, please provide a link so that I may be up to date. 

    The best recommendation would be a TVS diode on the RS-485 bus lines. The reference design IEC ESD, EFT, and Surge RS-485 Bus Protection Design Guide (Rev. B) shows three different solutions that the designer can use to increase surge robustness.

    Best,
    Andrew

  • 0 in reply to Andrew J
    Prodigy 10 points

    Hi Andrew 

    Thanks for the response,

    in the above mentioned guideline the varistor placed across A and GND, B and GND.  in Surge test procedures they saying Line to Line and Line to GND as below. 

    In that case do we need to one more varistor across A and B for Line to Line Surge test ( I'm considering 1KV surge pulse with 23A(42ohms series resistance for IO)) where the TVS is 17A capability

    kindly give clarity.

  • 0 in reply to Kumaresan N
    TI__Genius 17615 points

    Hello,

    Thank you for your question. Please allow us to get back to you on Monday.

    Regards,
    Aaditya Vittal

  • 0 in reply to Aaditya V.
    TI__Mastermind 29285 points

    Hello Kumaresan,

    A few key points on the inforamtion shown above.

    1. The TVS diode should be in parallel with the device it protects. The diagram above shows the TVS diode in series with the surge tester. This would result in the full surge pulse being discharged directly to the device. The parallel set up allows the discharge path to GND. 
    2. Another point is that the 17A clamping voltage is too low for your application. You would need a 24A TVS for the 1kV surge on each bus line to GND.
    3. The best solution TI has would be ESDS552 data sheet, product information and support | TI.com. 
      1. From my understanding, this device should protect both line to line and line to GND surges. 

    Please allow me to transfer this thread to the Protection Devices Group for them to provide better support since this is more of a surge related question. 

    Best,
    Andrew

  • 0 in reply to Andrew J
    TI__Expert 8310 points

    Hi Kumaresan, 

    As Andrew mentioned, ESDS552 is our best protection solution for RS-485 and is able to support 1kV surge events with 42Ohm series resistance. The max surge current for ESDS552 is 25A. Please check the link for more information on the IEC 61000-4-5 Testing procedure including line to line and line to GND (link).

    Please let me know if you have additional questions. 

    Best,

    McKenzie

  • 0 in reply to McKenzie Eaker
    Prodigy 10 points

    Hi McKenzie

    it helps a lot, while talking about surge strikes there is one more thing, number of strikes the component can withstand. For the varistor there is a calculation to find out the number of strikes this can withstand similarly do we have any on this.

    Also I like to know surge protection devices for LMR16030 based DC DC converter design. which applicable for Line to line and Line to GND surge tests.it will be good if I get any Reference design with EMI EMC protection.

    Thanks

    Kumaresan N

  • 0 in reply to Kumaresan N
    TI__Expert 8310 points

    Hi Kumaresan, 

    We don't necessarily have a formula for calculating the amount of strikes the device can withstand. We do conduct a test of 100 strikes for each device before it is released and always passes with flying colors. Recently, we conduct a million pulse test following the IEC 61000-4-2 which is shorter pulses compared to the IEC 61000-4-5 Surge test that is a longer pulse. It was on TSD05C and the part survived a million pulses. 

    For protecting LMR16030, we don't have anything in our portfolio to protect up to 60V. We are coming out with higher voltage surge devices in the coming year. 

    Best,

    McKenzie

  • 0 in reply to McKenzie Eaker
    Prodigy 10 points

    Hi McKenzie

    those 100 strikes is as per IEC61000-4-2 pulse or IEC61000-4-5 Pulse.

  • 0 in reply to Kumaresan N
    TI__Expert 8310 points

    Hi Kumaresan, 

    Originally, I thought only IEC 61000-4-2 but we also do 100 8/20us surge pulses following the IEC61000-4-5 standard. 

    Best,

    McKenzie