EEVblog Electronics Community Forum
General => General Technical Chat => Topic started by: BreakingOhmsLaw on September 18, 2022, 03:25:58 pm
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Hi everybody,
the datasheet of the IRFB7545PBF shows no connection for the tab of the TO-220 package. My guess is that it is isolated by an oxide layer from the other pins.
But what would the failure mode be? Could it get connected to any other pin?
https://www.infineon.com/dgdl/Infineon-IRFB7545-DataSheet-v01_01-EN.pdf?fileId=5546d462533600a401535619e1ca1e66 (https://www.infineon.com/dgdl/Infineon-IRFB7545-DataSheet-v01_01-EN.pdf?fileId=5546d462533600a401535619e1ca1e66)
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Isolated tab can, with overload that leads to overheating, short out to the drain, probably around the time drain, gate and source all bond into a single conductor, just about a millisecond before the smoke escapes at high velocity. Best o make sure this will not occur, or to at least add in extra protection physically, so an insulator will probably be a good idea, or an isolated heatsink, or connected to source instead for the low side, so a failure will cause a fuse to blow to provide protection. Not a good idea to have it connected to ungrounded metal heatsink at all, so for class II use you would always add in the extra isolation of a thermal pad and insulating clamp down hardware.
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Tab is almost guaranteed to be connected to center pin, it's just how TO-220 lead frame is normally made. As datasheet says nothing about isolated tab, I would not expect it to be the case.
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Tab is almost guaranteed to be connected to center pin, it's just how TO-220 lead frame is normally made. As datasheet says nothing about isolated tab, I would not expect it to be the case.
Guess I'm ordering a sample to measure that. Thanks!
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isolation voltage ?
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Some triacs have isolated tabs and this is advertised in the datasheet and maximum isolation voltage rating is provided (hundreds or low thousands of volts).
In absence of such data, there is no reason to assume it isn't just the usual TO220 construction: the tab and the center pin are cut from one piece of metal and soldered to the back of the die, which in case of vertical MOSFET is the drain.
If you require isolation, don't bother ordering it and look for some alternative in TO220F. Or ask the manufacturer for clarification, this information should be in the datasheet.
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Yeah, I thought you basically had to order TO220F, or use silpads, unless its TRIAC as mentioned.
They even show the D2PAK and the TO262 as tab connected, so just the TO220 being different would be kinda odd.