Comparing avalance ratings on mosfets

[eTobey]

Hi,

i am trying to compare two mosfets: TPH2R608NH https://toshiba.semicon-storage.com/info/docget.jsp?did=15733&prodName=TPH2R608NH and SiR180DP https://www.vishay.com/docs/76233/sir180dp.pdf. I found this very good video about this: https://www.youtube.com/watch?v=6CQj5s_cc5I.

When i calculate the Eav for the TPH (with the formula from the videos at 6:12), it does give me 58 mJ, but in the table in the Datsheet it says 149mJ. The datasheet for the sir has values as expected.

Is this a simple calculation error in the datasheet, or do they use tricks to make things look better?

[MarkT]

Do not ascribe to malice that which can be adequately explained by incompetence - probably a mistake.

I don't understand why anyone would ever rely on such a figure, avalanche breakdown in a MOSFET is never a good thing!  Especially the "single pulse" figure...

[Terry Bites]

Yes, its more a measurement of a fault condition and not a normal operating paramater.
Its a conditon that you need to protect against with good layout and snubbing circuits.

[eTobey]

I have thought about it. I came to the conclusion, that my mosfets in my BLDC driver never get into that state, because of the diodes of the complemmentary msofets.

[T3sl4co1l]

Notice the condition in note 5, VDD = 60V.  The inductor provides 57.6mJ of boost on top of the 60V supply.  We need to know the actual breakdown voltage to calculate this, which isn't easy to know: only a minimum (75V) is given, and it varies during the pulse anyway.  Using 90V as a SWAG, then the inductor would deposit 57.6mJ at 90 - 60 = 30V, but the device sees 90V therefore the total was (57.6mJ * 90V / 30V) = 172.8mJ.

Alternately, we can use the same argument to measure the average breakdown voltage.  Since they give the 149mJ figure, evidently Vbr is even higher, (60V) * (149mJ) / (149mJ - 57.6mJ) = 97.8V.

Which sounds like a generous safety factor, but there are multiple reasons to avoid operating continuously above the rated 75V.

The energy figures match up much more closely in most datasheets, where a lower VDD is used (for example, 10V supply into a 600V MOSFET); it is peculiar that they used such a high value here.

Tim