Author Topic: Single transistor with 7 pins!?  (Read 2365 times)

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Offline MrZwingTopic starter

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Single transistor with 7 pins!?
« on: February 20, 2017, 09:02:05 pm »
http://www.wolfspeed.com/downloads/dl/file/id/145/product/1/c3m0065090j.pdf

Why does this transistor have several "source" pins and what are the uses for it? i have been scratching my head quite a bit over this one.

does anyone have an answer for me why so many source pins? is there a special application for it?

/MrZ
 

Offline Benta

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Re: Single transistor with 7 pins!?
« Reply #1 on: February 20, 2017, 09:13:33 pm »
It has 5 source pins to keep resistance low. Drain is the tab, which is big enough.

 

Offline MrZwingTopic starter

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Re: Single transistor with 7 pins!?
« Reply #2 on: February 20, 2017, 09:15:46 pm »
so you hook up all 5 of them to source so the elektrons can pick and choose their way? :D
 

Offline Benta

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Re: Single transistor with 7 pins!?
« Reply #3 on: February 20, 2017, 09:28:30 pm »
so you hook up all 5 of them to source so the elektrons can pick and choose their way? :D

Yes. It's called "paralleling". A lot of us engineers use it in practice. If you grind off the top of the device, you'll also see 5 parallel bond wires.

« Last Edit: February 20, 2017, 09:31:00 pm by Benta »
 

Offline MrZwingTopic starter

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Re: Single transistor with 7 pins!?
« Reply #4 on: February 20, 2017, 09:39:16 pm »
ahh nice good to know sounds like a good practice.
 

Offline Phoenix

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Re: Single transistor with 7 pins!?
« Reply #5 on: February 21, 2017, 01:33:20 am »
One of the source pins is also called driver source. It's purpose is to provide a dedicated gate driver return path. This helps stop the gate driver being effected by the power current.
 

Offline T3sl4co1l

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Re: Single transistor with 7 pins!?
« Reply #6 on: February 21, 2017, 01:48:36 am »
Pins have equivalent inductance, and when you're switching, let's see, about 30A in 10 nanoseconds, every nanohenry counts.

Each pin on a D2PAK sized device has about 4nH inductance.  (For a regular D2PAK, that's all you need to know.  For this one, the pins are connected in parallel, so the inductances also act in parallel.  You can ignore coupling between them, for a wave-of-the-hands analysis.)

The Kelvin source connection, for gate drive, is very nice as well.

Homework 1: given the numbers I just wrote, how much voltage error, or overshoot, do you expect?  Where does that error appear in the circuit?  Why would it be important?  How much difference is there, using one pin versus all in parallel?

Homework 2: draw out the equivalent circuit of a transistor, including its pin/lead inductances, stray trace/wiring/PCB inductance, and so on for everything else in the power switching circuit.  Show us your schematic, and reflect on its meaning. :)

Tim
Seven Transistor Labs, LLC
Electronic design, from concept to prototype.
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