[sdiy] Question about a FET I stumbled across in a datasheet

ASSI Stromeko at nexgo.de
Fri May 8 21:45:15 CEST 2020

On Freitag, 8. Mai 2020 20:47:35 CEST Tom Corbitt wrote:
> My question relates to the 4th connection shown in the block diagram on
> page one (and later in the technical explanation) Just what the heck is the
> bottom element shown on the FET? (the lowest element under what I'd call
> the traditional source elements?) Is it the body?

No.  In any power MOSFET the body is tied to the source directly at the device 
and no separate body connection exists.

> Is this a special feature made/incorporated into this specific FET or is
> this something that you can do with proper biasing of the body?

Yes, that's a special feature of some power MOSFET (it's rare in discrete 
devices, but very common for integrated ones): this is a sense terminal that 
allows you to monitor the current.  One of the MOSFET fingers is separately 
wired out to that terminal to do that (it's another source, actually) and by 
being embedded in the actual power device it will have the same temperature, 
which is important for the current sense to be precise.  In  the datasheets 
you will find some parameter named kILIS or similar that tells you the sense 
ratio and how to connect it to an actual monitoring circuit.

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