I’m moving to a SOT-223 LDO that has 3 pins, and a grounding tab. All of the available schematic symbols I currently have have either 3, 5, or 6 pins. I can easily create a new one with 4 pins. However, I’m wondering that since there isn’t already one in the library, maybe people deal with grounding tabs differently? I guess for now, I’ll make a 4 pin component and mark the grounding tab as pin 0, but will change it if anyone can offer a more accepted approach… Thank you, as always.
Check out the pin numbering on this:
So, if you want to do it universal… stick to 1,2,3 for the small ones and 4 for the large tab for a SOT-223 housing.
The symbol then also needs 4 pins.
Don’t use ‘0’.
If you’ve got a device in that housing that only has got 3 electrical pins (symbol then has got 3 pins only) and you know what you’re doing you can also just use 3 pin numbers on the footprint (which means 2 pins will have the same number) - caveat then, you have to have a special footprint for this device.
Or you put 2 pins in the symbol with different numbers (one has to have invisible numbering then) over each other, so they get connected at the same time to the same net (that solution is not so ‘clean’), so the footprint can have 4 numbers - caveat, hard to modify symbol if more than 10 pins involved stacked on top of each other.
Many ways lead to Rome…
Personally I’d do either the first or second variant… the third is not easy to spot/handle once implemented.
There was a post a couple of days back about this kind of thing though, which was proposing a way to have pin-linking-options in the symbol-editor… one sec…
Read through the thread and if possible log/register on launchpad to support the proposal to get a feature like this implemented - click on “this bug affects me” too at top left
You’re stuck with either a clunky, somewhat non-standard schematic symbol; or a custom footprint that applies to a relatively small number of parts. “For every solution, there’s a problem!” as a former supervisor used to say.
I faced an essentially identical problem with a 3-terminal regulator in TO-220 package a few weeks ago. I discussed my approach in the thread, “Multiple Pin Components” at Multiple pin components
If the component datasheet identifies pins as “1”, “2”, “3”, “4”, then I’d try to stick with that in both symbol and footprint to the extent that you can. Creating “Pin 0” seems like a bad idea to me, also.
Thanks – I was thinking pin 0 since the datasheet didn’t have any number for the grounding tab, so I was winging it. Looks like I should delete my custom schematic symbol.
Super helpful, thanks!!! I’ll rework my design later tonight.