What should be done to the multiple collector pins on a quad NPN SMD?

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phillipsoasis

Joined Aug 22, 2022
80
I am thinking of using a FFB2222A / FMB2222A / MMPQ2222A which is a SMD with 4 NPN transistors to drive some LEDs from a Raspberry Pi. This is my first foray into SMDs. It comes in a 16 pin SOIC. Each collector is connected to two pins, and it shows that they are shorted together internally on the chip. I was wondering if I should I connect the related collector pins together when I connect to them, or just connect to one of the collector pins. There isn't anything in the datasheet that says what to do with the dual collector pins.

I have attached the schematic of my project and a copy of the datasheet. If there is another part that would be more suitable, please let me know that as well. Just need something cheap to pull ~20 mA through each of the LEDs.

Thanks!
 

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ronsimpson

Joined Oct 7, 2019
3,229
I like what Dick did. It keeps me from downloading the data sheet and digging through pages of unrelated data. My internet is not fast, and the computer is old.
 

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phillipsoasis

Joined Aug 22, 2022
80
Tie them together to a copper land, this serves as an improved thermal path to help cool the die.
By "copper land" do you mean a zone (like pins 6 and 5 in the attached image) or a 0.5 mm track (or bigger?) connecting them (pins 8 and 7 in the attached image)? I am using KiCad 7 for schematic capture and PCB layout.
 

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ronsimpson

Joined Oct 7, 2019
3,229
By "copper land" do you mean a zone
If the part is used at low power, I would probably just connect up traces like C1,&2 and not like C5&6. Just to be fast. If the part is running warm or hot I would add as much copper as possible more like C5&6. I work in high temperature high power environments. I would do an area fill to pick up all the ground pins with the max amount of copper.

Copper pulls heat away from the IC. Fiberglass is an insulator and keeps the heat at the IC.
 

Thread Starter

phillipsoasis

Joined Aug 22, 2022
80
I like what Dick did. It keeps me from downloading the data sheet and digging through pages of unrelated data. My internet is not fast, and the computer is old.
I now understand Dick's intent, which was helpful to others. Perhaps if Dick had added a couple of words to his post there would not have been any confusion.
 

Thread Starter

phillipsoasis

Joined Aug 22, 2022
80
If the part is used at low power, I would probably just connect up traces like C1,&2 and not like C5&6. Just to be fast. If the part is running warm or hot I would add as much copper as possible more like C5&6. I work in high temperature high power environments. I would do an area fill to pick up all the ground pins with the max amount of copper.

Copper pulls heat away from the IC. Fiberglass is an insulator and keeps the heat at the IC.
When I look at the Vce/Ic chart, at Ic = 20 ma, Vce = 0.5 V, so 40 mW per NPN when on. 80 mW per chip. These chips are rated for 300 - 1000 mW Device dissipation. The derating value is 8 mw/C above 25C, so the chip, when all LEDs are on will be running at 35C. Does that warrant a zone or just a track? Did I figure that correctly?
 
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