SOT223 and pins

Marco Trapanese wrote:

Hi,

 

I know we can assign a pin to two or more pads. Sometimes this is

necessary, indeed.

 

For example a SOT223 has four pads and usually the middle is connected

to the exposed one.

 

In the schematic makes no sense to show two pins: let's think a mosfet

with two drains....

Well, that is exactly what I end up doing.  Although it seems ugly at first,

it actually makes good sense.  For example, I have a MOSFET on a schematic

in front of me right now.  It's in a 4-pin DIP package, and looking at my

schematic I can see that the drain is connected to pins 1 and 2, because

both of those pins are shown on the symbol.  If the schematic symbol only

had one drain pin shown, then I wouldn't be able to see both those pin

numbers, and I might have to pull out the datasheet to figure out what that

unknown pin is for.

What do you do to make the schematic readable and the layout correct

(e.g. both pads connected) ?

Clench your teeth, put the multiple pins in the symbol, and with time you'll

get used to it....

Thanks

Marco / iw2nzm

--

Bert Menkveld

Bert Menkveld ha scritto:

Clench your teeth, put the multiple pins in the symbol, and with time you'll

get used to it....

I won't get used to it..l It's a lack of the CAD. I've never seen a

schematic like that. It should show the actual function of the pin

rather the physical connection.

Marco / iw2nzm

Marco Trapanese ha scritto:

Clench your teeth, put the multiple pins in the symbol, and with time

you'll get used to it....

Furthermore there is another bad thing. Many voltage regulator share the

same packages. So it would be nice to have only one device with several

variants, one for each package version.

Simply it is not possible. TO92 or TO220 have three pins, SOT223 has

four pins (GND pin and GND tab) so they can't live togheter. Ok, I need

two devices. But let me say it's a "bit" trivial...

Marco / iw2nzm

Marco Trapanese wrote:

Marco Trapanese ha scritto:

 

Clench your teeth, put the multiple pins in the symbol, and with

time you'll get used to it....

 

Furthermore there is another bad thing. Many voltage regulator share

the same packages. So it would be nice to have only one device with

several variants, one for each package version.

 

Simply it is not possible. TO92 or TO220 have three pins, SOT223 has

four pins (GND pin and GND tab) so they can't live togheter. Ok, I

need two devices. But let me say it's a "bit" trivial...

I agree with you on this one.  It is unfortunate that you end up having to

make separate devices for the same part in different packages.  I wish some

bright guy at CadSoft would think of a way around this.

Maybe an "optional" setting for symbol pins?  That way a symbol pin might or

might not be used when connecting it to a package in a device.  I wonder

what kind of problems that might lead to....

--

Bert Menkveld

Marco Trapanese wrote:

For example a SOT223 has four pads and usually the middle is connected

to the exposed one.

 

In the schematic makes no sense to show two pins: let's think a mosfet

with two drains....

Sometimes it is useful for making efficient routing and use the drain

pins to jump.

But in other cases i agree with opinions in this thread...