STW56N60DM2: Isolated back tab, or connected to drain?

[JW2112]

Hello all,

   I'm looking at the datasheet for the STW56N60DM2, and it's really not clear if the back of the FET is electrically isolated from the Gate, Source, and Drain. Typically, this is more clear in other datasheets I've looked at. Below is the only "hint" I can find that the part is isolated.

The image below is from a different manufacturer, and they make it much easier to determine.

[Peter BENSCH]

Welcome @JW2112, to the community!

If it is not explicitly listed in the data sheet as an isolated package, the metallic back side of the TO-247 is always connected to the centre connection. In this case, this back side and pin 2 are therefore connected to the drain.

Does it answer your question?

Regards
/Peter

[Peter BENSCH]

An additional note, because I've only just seen the second part of your question: the other manufacturer doesn't call its package TO-247 either, but ISOPLUS247, which already indicates the difference.

[JW2112]

Hi Peter,

   To add to the confusion, here's one from an ST part that shows the back tab IS electrically connected to the drain.

[Peter BENSCH]

Which device are you talking about right now?

[JW2112]

The part with the tab and drain shown together is the STW65N60DM6. I've attached it to this reply. Thanks!

[Peter BENSCH · Accepted solution]

Ah, now I understand what you mean:

• the drawing in data sheet for the STW56N60DM2 states: D(2)
• the drawing in data sheet for the STW65N60DM6 states: D(2, TAB)

This may seem confusing at first, but packages such as TO-247 or TO-220 have had this structure for decades. If the transistor or diode die is mounted isolated in such packages, this is explicitly mentioned in the data sheet, as mentioned above. Conversely, if the data sheet does not say anything about isolated, then it is not isolated.

Regards
/Peter

[JW2112]

Hi Peter,

    I ordered some of STW56N60DM2 and STW48N60DM2 and verified that the datasheet doesn't accurately depict the status of the connection between the case tab and the drain pin. The case tab and drain pin are indeed shorted. Does ST make something similar to the two parts mentioned in a TO-247 package that do have the back tab isolated?

[Peter BENSCH]

I can only repeat myself: the TO-247 always, i.e. always has the connection between the centre pin and the tab.

Only the 4-pin version TO-274-4 is mounted slightly differently, where pin 1 (a little further away = air and creepage distance) and tab are usually connected.

Insulation is achieved either by completely encasing it in molding (e.g. with TO-220FP), or by insulating the MOSFET die by means of a ceramic disc, for example. However, both insulations have a serious disadvantage: the thermal resistance increases drastically. Such a package, even if it looks like TO-247, is not a TO-247, but e.g. an ISOPLUS247 or whatever the respective manufacturer calls it.

The answer is therefore: no, STMicroelectronics does not have a MOSFET in TO-247, where the tab is internally isolated.

Regards
/Peter

[JW2112]

Hi Peter,

    Sorry about that. I must have misinterpreted your previous comment:

• the drawing in data sheet for the STW56N60DM2 states: D(2)
• the drawing in data sheet for the STW65N60DM6 states: D(2, TAB)

"This may seem confusing at first, but packages such as TO-247 or TO-220 have had this structure for decades. If the transistor or diode die is mounted isolated in such packages, this is explicitly mentioned in the data sheet, as mentioned above. Conversely, if the data sheet does not say anything about isolated, then it is not isolated."

I read that as the data sheet IS calling out the STW65N60DM6 as the back tab connected and the STW56N60DM2 is not. I'm curious as to why there is a discrepancy in the way this is called out on a data sheet?

Thanks.