Having read this app note (and a few others) and quite a number of TVS datasheets, I came across one that is bugging me a bit.

All of the TVS datasheets that I have read so far describe the the following concept (below curve is for a unidirectional TVS, but the same principle applies for a bidirectional TVS):

TVS curve

Thus, to generalize, the following seems to always be true:

\$V_{RWM} < V_{BR} < V_{CLAMP} \$

Then I read the datasheet of the Vishay XMC7K24CA and saw this:

TVS specs

From that table, \$V_{CL, max} < V_{BR, min}\$ (and \$V_{BR, max}\$ for that matter). This does not correspond with the general TVS curve above. How is this possible?

EDIT: Yet another datasheet (DIODES DESD18VS1BLP3) that shows the same:

TVS specs 2

I am definitely misunderstanding something here...

  • 1
    \$\begingroup\$ It can happen. I think it's called "snapback". Google app notes about that. There are also two terminal thryistors that take this to the extreme by breaking down to conduct at a very low voltage to crowbar. \$\endgroup\$
    – DKNguyen
    Apr 8, 2021 at 3:56
  • \$\begingroup\$ Take a look at figure 5 of the DIODES datasheet. This is where the higher breakdown voltage at 1mA comes from i would assume. Maybe somebody can explain the graph? \$\endgroup\$ Apr 8, 2021 at 4:41
  • \$\begingroup\$ Found a good article regarding the snapback described above: blog.semtech.com/tvs-its-just-a-diode-right-part-two \$\endgroup\$
    – Ste Kulov
    Apr 9, 2021 at 1:24
  • \$\begingroup\$ This is indeed the "snapback" effect (a.k.a. thyristor-like characteristic) and seems to be quite common in some TVS devices. I learned something new today :) \$\endgroup\$
    – wave.jaco
    Apr 9, 2021 at 3:50

1 Answer 1


This device has a thyristor-like latching characteristic. Here is a simulation of the SPICE model supplied by the manufacturer:

enter image description here

  • 1
    \$\begingroup\$ Thanks. This is indeed a thyristor-like characteristic (also called "snapback") of the device. I first had to do some reading to understand this, but now it all makes sense. \$\endgroup\$
    – wave.jaco
    Apr 9, 2021 at 3:48
  • \$\begingroup\$ The datasheet is less than helpful and I couldn't find any more information from Vishay on it, other than the SPICE model. They also don't appear to use the "snapback" term, but it's definitely a useful addition to the lexicon, thanks to @DKNguyen for that. \$\endgroup\$ Apr 9, 2021 at 3:57
  • \$\begingroup\$ You are exactly right. I was searching for "snapback" term and couldn't find it, even in other similar datasheets as well! That is part of the reason why I was so confused. Although, I must admit, I did not know about "snapback" TVS diodes up to now. I learned a lot through your answer & comments to this question. \$\endgroup\$
    – wave.jaco
    Apr 9, 2021 at 6:44

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