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SOT223; Joining pad to tab

e14 Contributor

Hi folks.

 

I'm having a problem with using the tab on SOT223 voltage regulators that use the tab as a heatsink and is usually the same connection as the centre pin. But when I add a  polygon around it to increase the surface area, it either leaves the centre pin disconnected or the tab is isolated.

 

Is there a nice way to achieve this?

 

Thank you.

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  • 0 in reply to e14 Contributor

    You are right, the schematic symbol should have a pin for each pin on the device. You can edit the device to add the pin. You could check the 78L05F device in the Linear library to see how they did it there in the SOT89, but note they connected the 2 pins in the device package.

    The LD117AS12TR device in the V-Reg library has an unconnected pad, you can just add a pin to the symbol and connect it in the device window, or create a new symbol with 4 pins.

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  • 0 in reply to dougw

    Thank you for your help. I have finally solved it !

     

    As you say, I've edited the part after finding it in the library and added a pin which was the easy part.  What I had to do then was to "connect" it which was a little complicated and took me a while to find out how.  I saw a "Connect" tab in the lower right window but I've forgotten how I got there. Anyway, this shows you the pins and pad connections. I got confused with the centre panel, as anything in there got added to the top right panel, sometimes with a link symbol, and sometimes a broken link symbol. I'm sure I can find out why eventually, but I did manage to get 4 pins connected to 4 pads, and got a green tick. After saving, this was easy to replace the part I had  - and gave me that extra connection on the schematic. When this was connected, I got an airwire on the board which was correct. Clicking ratsnest filled it in as my ground around the pad with no gaps!

     

    So happy.image

     

    One wrinkle is the pin is given a name which I couldn't see a way to edit that at the time, but maybe it is easy to re-name it before I placed it.