Why does this schottky diode have three pins

Question

I'm just wondering why this schottky diode have three pins?

I know two of the pins acts like rectifier but what does the a third pin do?

Source:

For the diode in question, nothing http://www.semicon.panasonic.co.jp/ds4/DB3J208K_E.pdf. It's a reasonable question though why *some* SMD diodes are packaged like this. That's in fact not too different than the (more general) recent hot question: http://electronics.stackexchange.com/questions/194693/why-do-ics-have-nc-no-connection-or-no-function-pins — Fizz, Oct 13 '15 at 12:57
@Olin - The datasheet tells that pin 2 is not connected (NC) but doesn't say why the three pin package is used instead of a two pin one. The question isn't dumb nor directly answered in the datasheet *at all*. — Ricardo, Oct 13 '15 at 13:58
@Ricardo The OP asked what the third pin does, which is answered directly in the datasheet. If he didn't know why some packages have N/C pins, he should have done a little research before asking here. Those answers were also right in front of him. This was a question that could be answered easily if he'd done a little bit of research first. — DerStrom8, Oct 13 '15 at 14:27
I'm glad someone asked (as usual you get a bunch of useless moral police dudes spending their time in order to censor others, for every single useful answer hero). — JinSnow, Nov 08 '22 at 20:58

score 13 · Accepted Answer · answered Oct 13 '15 at 12:43

13

In general, single diodes in 3-lead SM packages have no connection on the third pin. This is a fairly common practice in the industry.

I don't have a solid answer as to 'why' they do this, but will share a few possibilities for debate:

You cannot install a single diode in a 3-lead package with reverse polarity because of the asymmetry of the package; if the diode were in an 'inline' 2-lead SM package (like SOD323) there is a chance of reverse installation
3-lead packages are larger, allowing for larger die sizes (better thermal performance), easier installation by pick-and-place machinery (generally, the smaller the part, the trickier installation is) and easier optical inspection

answered Oct 13 '15 at 12:43

Adam Lawrence

possibility to add a heatsink – YoussefDir Feb 29 '20 at 13:35
Far too small for practical heatsinking in my opinion. Also with dense SM layout you would not likely be able to route much copper to it, and if you connect the pin to a heavy internal copper layer with vias you would have a very hard time soldering that pin properly. – Adam Lawrence Mar 02 '20 at 15:33
There are also dual Schottky diodes packaged into a single sot-23, like the [BAT754 series](https://docs.rs-online.com/8aef/0900766b80b4a0df.pdf). In that case, the third pin is connected to the second diode's anode or cathode. – Philip Sep 13 '21 at 16:33

1 Answers1