# Thermal Resistance, Junction to Ambient, Effective 4 Die

1. ## Thermal Resistance, Junction to Ambient, Effective 4 Die

I am not a beginner in electronics, but this question may be. I know what thermal resistance for a package is, but I have a question for somebody. I am looking at an IC that has 4 2n2222 transistor in it (MMPQ2222A). It is an SOIC-16 package. Now, there are two ratings for the thermal resistance: Each Die, and Effective 4 Die. The effective 4 die is 125C/W and Each Die is 240C/W. Is the thermal resistance for the package actually 125C/W because there are four dies in it? Is the the thermal resistance if all 4 transistors are operating? Why give the Each die figure if the 4 die figure is really the correct one? I have googled all over on this and have not obtained an answer. Fairchild has not responded yet either. Confused. •

2. ## Thermal Resistance, Junction to Ambient, Effective 4 Die

If just one of the transistors is dissipating significant heat you would need to use the 240 value. While the package may be 125, that is only when the heat spread is from all transistors evenly.

Keith •

3. ## Re: Thermal Resistance, Junction to Ambient, Effective 4 Die

So if one transistor is dissipating 1W then use 240C/W.

If four transistors are dissipating 1W then use 125C/w.
(1 Watt total, not each.)

Got it.

If three transistors are dissipating 1W then interpolate between 240 and 125.
(1 Watt total, not each.)

Interesting: 240/4=60. Coupling between the dies is not surprising. --[[ ]]--