For my design I need a bunch of 2222A transistors with each transistor dissipating at maximum ~500mW of power. The transistors come in single packages, dual packages, and quad packages. The datasheet has it listed as "Total Device dissipation" for the single at 300mW, "Total Device dissipation" for the double at 700mW, and "Total Device dissipation" for the quad at 1000mW.
Does "Total Device dissipation" refer to the individual transistor(s) in the package or to the entire package?
https://www.fairchildsemi.com/datasheets/FM/FMB2222A.pdf
Edit: None of the answers have really made me feel its confidently its one or the other so here's another way we could answer the question maybe more definitively.
TI has a document on understanding power dissipation:
http://www.ti.com/lit/an/slva462/slva462.pdf
The unit in question is \$P_D\$ on the data sheet. TI tells us that this value can be derived from the following equation. Maximum Power Dissipation \$P_{DMAX}\$ is defined as the following
\$P_{DMAX} = \frac{T_{JMAX}-T_A}{\theta_{JA}} \$
From the data sheet it gives maximum operating junction at \$T_{JMAX} = 150C\$
The ambient temperature will be room temperature which is \$T_A = 25C\$
The question now is what does the data sheet means by "Thermal Resistance" \$R_{\theta JA}\$?
For the single package it has "Thermal Resistance, Junction-to-Ambient" at \$R_{\theta JA} = 415C/W\$ which does equate to 300mW. So for the single package no doubt it has a dissipation of 300mW for the package and device
For the double it has "Thermal Resistance, Junction-To-Ambient" at \$R_{\theta JA} = 180C/W\$ which equates to ~700mW.
For the quad it has two different paramters. "Thermal Resistance, Junction-to-ambient, Effective 4 dies" \$R_{\theta JA} = 125C/W\$ which equates to 1000mW
and it has "Thermal Resistance, Junction-to-ambient, each die \$R_{\theta JA} = 250C/W\$ which equates to ~500mW
For the double package it almost seems as though thermal resistance refers to each individual transistor making each device have a consumption of 700mW and the whole package a consumption of 1400mW
For the quad package it seems like effective 4 dies means divide result by 4 so each transistor dissipates 250mW but then it says each die and results in 500mW.
So I am again still confused. Thoughts?
Best Answer
It's per package, also you will have to derate for ambient temperature so the maximum per transistor is the dual at 350mW per transistor at 25'C.
However note that that puts the junctions at 151'C at 25'C Ta. The 25'C ambient maximum is unrealistic in most cases, and 151'C is very high if you care about reliability. Personally I think more like 150mW per transistor would be more conservative. That would yield a Tj of about 125'C at Ta = 70'C.
If you need a nominal dissipation of 500mW per transistor, I suggest individual TO-252 or at a minimum SOT-89 transistors, mounted on an adequate area of copper.
Just as an aside, it's unusual to have a wimpy transistor like a 2N2222A dissipating 1/2-W, there could be other issues cropping up like SOA. Makes me think you might be doing something wrong, but that's just a guess, feel free to ignore if you are all set.