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Shottky diodes for USB ESD
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Blitzschnitzel:
Hi,
I am designing a small USB numpad and I am adapting someone else’s design. I want to keep everything except the MCU through hole. The design has two ESD protection diodes in it. Which makes sense but I don’t know what to make of the rating of the Schottky diodes.
I’ve looked at the shottky diodes from my local supplier and forward voltage ends at 2.5v and reverse voltage starts at 8v. So, I really don’t know how to read the marked 3.6v. Does the guy perhaps actually mean Zener diodes? And if it were Zener diodes, wouldn't you pick something close to USB's 5v? What kind of diode would you pick for this?

Twoflower:
Usually this are TSV diodes. But I don't think that you'll find some through hole types as USB is a bit demanding. There are single diodes and full networks available (protecting also the supply lines). But the only ones I found was SMD, sorry.

Maybe here's some information about the different types of USB ESD protection: https://www.we-online.de/web/de/electronic_components/news_pbs/blog_pbcm/blog_detail-worldofelectronics_108785.php.

Edit: Fixed the link (the . at the end does not belong to the link as the Forum-SW thinks)
HwAoRrDk:

--- Quote from: Blitzschnitzel on October 16, 2019, 12:41:32 pm ---And if it were Zener diodes, wouldn't you pick something close to USB's 5v?

--- End quote ---

The data lines for LS and FS USB use 3.3V (or is it 3V? I forget).
Blitzschnitzel:

--- Quote from: Twoflower on October 16, 2019, 01:06:41 pm ---Usually this are TSV diodes. But I don't think that you'll find some through hole types as USB is a bit demanding. There are single diodes and full networks available (protecting also the supply lines). But the only ones I found was SMD, sorry.

Maybe here's some information about the different types of USB ESD protection: https://www.we-online.de/web/de/electronic_components/news_pbs/blog_pbcm/blog_detail-worldofelectronics_108785.php.

--- End quote ---
Ah, It's called TVS. I am wiser already. Yes through hole TVS diodes seem to start at minimum 6v.


--- Quote from: HwAoRrDk on October 16, 2019, 01:17:10 pm ---The data lines for LS and FS USB use 3.3V (or is it 3V? I forget).

--- End quote ---
Thanks I didn't know that.

So, in this case I would either try normal Zener diodes or leave out the ESD protection. Would a normal Zener still somewhat help or would it actually be detrimental to the design?
Twoflower:
Not sure why you're insist to use through-hole. Especially since you say you have a SMD processor.

And if you use a SOT8 to DIL8 adapter? OK, that's not fully through hole anymore, but that brings your on the safe side to protect the PC and your own circuit. For example the ST USB61. That device provides a core or less complete protection. And SOT8 is normally easy to solder (pin to pin 1.25mm). It seems that there was a B2 version in a DIL8 package. But I haven't seen anything else but the datasheet.
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