SSOT package amperage

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Sergio34

Joined Nov 10, 2018
52
Hello, somehow I ended up buying these MOSFET, sometimes when I cannot find the through hole component I need I buy the smd version and I find a way to solder it on the through hole board. I knew it was going to be small but I did not expect it so small.. After I bought them I realised that there were other through hole MOSFETS I could had purchased. Anyway the datasheet (attached) says it can handle 4A of continuous current. Assuming it is turned on fully can really a so small component handle 4A? Is not an error? Also why the drain pins 1,2 and 5,6 are not made together from the factory as tabs on each side? But still 4A would have to pass through the source pin which is so tiny. I believe even 4A wire is more beefy. Maybe I am asking because once upon a time I made a short circuit, wires became very hot on my hands and I have trauma from then...
 

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jpanhalt

Joined Jan 18, 2008
9,425
Hello, somehow I ended up buying these MOSFET, sometimes when I cannot find the through hole component I need I buy the smd version and I find a way to solder it on the through hole board. I knew it was going to be small but I did not expect it so small.. After I bought them I realised that there were other through hole MOSFETS I could had purchased. Anyway the datasheet (attached) says it can handle 4A of continuous current. Assuming it is turned on fully can really a so small component handle 4A? Is not an error? Also why the drain pins 1,2 and 5,6 are not made together from the factory as tabs on each side? But still 4A would have to pass through the source pin which is so tiny. I believe even 4A wire is more beefy. Maybe I am asking because once upon a time I made a short circuit, wires became very hot on my hands and I have trauma from then...
Look at the heatsink requirement. DIP size is quickly disappearing. Resign yourself to horse and buggy or learning how to handle heat in SMD.
 

Thread Starter

Sergio34

Joined Nov 10, 2018
52
Look at the heatsink requirement. DIP size is quickly disappearing. Resign yourself to horse and buggy or learning how to handle heat in SMD.
Sure thing, I like learning, just wanting to make sure I am on the right path of learning. Thanks!
 

dl324

Joined Mar 30, 2015
10,750
But still 4A would have to pass through the source pin which is so tiny. I believe even 4A wire is more beefy.
The current capacity is more limited by the bonding wires from the semiconductor to the leadframe. For high current devices, they use multiple bonding wires.
clipimage.jpg

Here are the currents allowed based on modified Preece equations:
clipimage.jpg
A 1mm long 2 mil (mil = 0.001") bond wire can carry 4+ amps. The thickness of a sheet of 20# paper is 4 mils (https://www.jampaper.com/paper-weight-chart.asp).

Bond wires used to be gold, some are switching to copper.

WH Preece derived metal fusing equations in the late 1800's.
 

Thread Starter

Sergio34

Joined Nov 10, 2018
52
The current capacity is more limited by the bonding wires from the semiconductor to the leadframe. For high current devices, they use multiple bonding wires.
View attachment 208523

Here are the currents allowed based on modified Preece equations:
View attachment 208522
A 1mm long 2 mil (mil = 0.001") bond wire can carry 4+ amps. The thickness of a sheet of 20# paper is 4 mils (https://www.jampaper.com/paper-weight-chart.asp).

Bond wires used to be gold, some are switching to copper.

WH Preece derived metal fusing equations in the late 1800's.
This is amazing knowledge you provided, it’s the missing piece of the puzzle to comprehend the microworld. Thanks a lot!
 

dl324

Joined Mar 30, 2015
10,750
This is amazing knowledge you provided, it’s the missing piece of the puzzle to comprehend the microworld.
While I was checking this, I found a document from Alpha & Omega Semiconductor Inc that said the device was the current limiter.

What I recall from the late 70's when I first got involved with semiconductor layout is that typical maximum current density in the aluminum conductors was on the order of a million amps/square cm.
 

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