Transistor Package TO-261 Case style [5-Terminals]
TO-261 Package Drawing, 5-Terminal
Tab mount. A package type that uses a tab for attaching the semiconductor to a heat sink to achieve thermal management of the semiconductor case. Tab 5 of this package may be used to dissipate heat into the Printed Circuit Board [PWB].
When attached to a PWB a large copper pad should be located underneath the thermal tab of the TO-261. The larger the copper pad, the lower the thermal resistance and the better the heat transfer. Metal tabs attached to the semiconductor body usually mean the component can dissipate more power than an identical package without a tab, having a normal terminal lead instead.
Body temperature. Case temperature is that temperature measured at a specified point on the semiconductor case. When comparing two data sheets make sure that both data sheets define the same location of the thermocouple on the case. Heat dissipation is this case is handled by the metal tab, which is also terminal 5.
Note that some data sheets may consider this as a 4 pin package, not counting the tab as a terminal.
The TO-261 may also be designated as a SOT-223.
Note that some data sheets may indicate that the graphic defines the package type and that the number of leads may be different. That comment is true for many package types listed on this web site, as many components using a particular TO-number might have any number of terminals. This package is common in both 4 pin and 5 pin versions. As with any package the function of the pins might change depending on the actual device placed within the package.
Both the 4 pin version and 5 pin SOT-223 version is commonly used as a voltage regulator. When used as a regulator the tab is normally used as a ground terminal for the 5 pin version or V-out on the 4-pin version. However the 4 pin version is commonly also used to hold a high power transistor or FET. When the SOT-223 is used as a transistor, the tab is duplicated as pin 2 and used as the collector. If the SOT-223 is used as a FET than the tab, along with another pin might be used as the drain. The point is that when only three leads are required the tab is reused as another terminal to dump additional heat from the package; there is no rule so check the data sheet.
Editor note; although the package dimensions are accurate; be sure to follow what ever Land Pattern is provided by the manufacturer when designing the printed wiring board.
