Internal connections
Drawing a part having internal connections
We look for example at a Power Mosfet CSD 1730 8Q3 from Texas Instruments that "has been designed to minimize losses in power conversion applications and optimized for 5V gate drive applications" Data sheet
The symbol shows the source connections 1, 2 and 3 are linked as well as the drain connections 5, 6, 7 and 8. Lediglich der Gate-Anschluss 4 liegt für sich. Die Aufgabe lautet nun: Aus acht mach drei!, denn das Gehäuse hat acht Kontakte. Es muss durch das interne Zusammenschließen mit nur drei Signalen klar kommen, ohne Kurzschlüsse zu melden.
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Das Zusammenschließen von Pins im TARGET 3001! Schaltplansymbol erreicht man durch Übereinanderlegen. Zeichnen Sie in TARGET 3001! also ein Symbol mit acht Pins und schieben Sie die Pins eins, zwei und drei deckungsgleich übereinander. Gleichermaßen verfahren Sie mit den Pins fünf, sechs, sieben und acht. Das Resultat sieht so aus:
Bild: Symbol des genannten Power-Mosfets mit internen Verbindungen, wie es sich in TARGET gezeichnet darstellt.
Bild: Draufsicht des Lötfüßchenmusters des genannten Power-Mosfets, wie es sich in TARGET gezeichnet darstellt. Acht Kontakte des Gehäuses SON3.3mm X 3.3mm wollen angelötet sein.
Ein Signal zwei Lötpunkte
In a component several pins/pads might internally be connected in order to have electrical load capacity. So they can be used like a brigde. For example in a connector one terminal can be connected to several pads:
Both connections are needed to give mechanical stability. If the current load is low both connections can have separate pads. So the internal connection might be used like a bridge. Route close to one of the pads and continue routing with the other. The gap in between can be used routing through to it. But if the current load is high it might be necessary to connect both pins by a current leading piece of track.
For the fact that the decision for the load capacity in most cases is not made by the designer of the part, the user of this part needs to confirm the connection. In the layout just draw two normal pads not touching each other. In the schematic create two pins as well but place them exactly superposed to each other:
During the drawing of this symbol two pins showing the length of zero have been used. The pin names have been deleted. If several poles of the same signal in a package are wanted, several connections need to be placed superposed to each other in the symbol: 1+2, 3+4, 5+6 ...
The pin numbers 1+2 are automatically displayed side by side later:
If more than 2 pins represent one pole in a connector then the pins are combined as three: 1+2+3, 4+5+6, ... Such a combination in TARGET is called "cluster".
In a package being already placed to the layout please click M11 upon its handle cross. Use button [Internal connection] while the dialog "Change packages" flashes. Now the pins belonging to each other can be combined to clusters. If the pins in the schematic already are superposed to each other correctly then just confirm the proposal. In consequence TARGET combines all clusters automatically.
Other CAD systems (e.g. Eagle) require the decision whether pins are internally connected already when drawing the part. The properties "all" and "any" are used in a "Connect" context. "all" for: all pins need to be connected, "any" for: it is sufficient to connect any pin. This may lead to problems later because the designer of the part can not know, how heavy the electrical load later will be. A push button with one pin and a 2x2 connection in a motor control sure won't lead the complete motor current through its small package just only because 2 pins are joint together to GND:
