TVS diode design for surge voltage

[ku637]

Hi,

I want to design a protection circuit to a CAN data line using a TVS diode against IEC61000-4-5 Surge waveforms

I've some questions

1) The IEC standards specify current waveforms of 8/20uS and voltage wave forms of 1.2/50us. Can anyone tell me what is the purpose of two waveforms?Which one should be used for designing the protection using TVS.



2) https://www.lisungroup.com/IEC61000-4-5.pdf

page 27 describes the relation between peak current and voltage..How does that established? On looking i think the impedance factor is considered as 2Ohm ,what is that impedance , is it the impedance of my communication lines?

3)The TVS diode im considering is PESD2CAN from NXP, how to properly calculate whether it will withstand a IEC Surge of 2kV

www.nxp.com/documents/data_sheet/PESD2CAN.pdf

4) The clamping voltage requirement is around 45V.

5) The peak pulse current of PSD2CAN is specified as 5A for 8/20uS waveform. ( but 2kV/2=1kA)

Any experienced hands can guide me how to begin?

Thanks for any help

 

[chuckey]

the waveforms are based on an " average" lightening strike. The lightening is a constant current generator, but the voltage is what is expected when the current hits your piece of kit. Must be some Cs and Rs in the atmosphere!!
Just looked the .pdf for the diode. This for protection of an in-car bus - right, why do you think lightening will be a problem, the car its self is a Faraday cage. This is why the current tests are done at 5 A and not the more typical 1KA which lightening protection devices are tested at. Likewise this diode can withstand up to 30KV static discharge, so 2 KV would seem to be a dodle. I expect that its tied up with the energy levels (how much current can flow). I have been involved with lightening protection but only at the "heavy" end and not with individual chips and devices, so I would have to study the relevant documents to figure out what they are after. It could be advantageous to look at other OEMs of diode protection devices, just to see if they explain and show how their devices meet the relevant specs.
Frank