Tek-Tips is the largest IT community on the Internet today!

Members share and learn making Tek-Tips Forums the best source of peer-reviewed technical information on the Internet!

Register Log in
  • Congratulations cowski on being selected by the Eng-Tips community for having the most helpful posts in the forums last week. Way to Go!

Junction vs. Case Temperatures

Status
Not open for further replies.
EngAP

EngAP

Mechanical
Joined
Jun 6, 2007
Messages
52
Location
GB

Quick question from a mechanical engineer to electrical engineers:

How much hotter is the junction temperature compared to the case temperature for a chip?

Is there a range it is likely to fall within or is this a much too vague question?

Specifically, if the spec for maximum junction temperature is stated as 100degreesC what would you recommend the chip case temperature be limited to? Just looking for a ball-park figure for initial calcs.
 
Sort by date Sort by votes
Depends on the die-to-case thermal resistance, which varies ALL OVER THE PLACE. You need to look at the datasheets.

TTFN

FAQ731-376
 
Upvote 0 Downvote
and of course the power dissipated. The temperature difference between junction and case is the thermal resistance junction-to-case (degC/W) multiplied by the power in the chip (Watts).
 
Upvote 0 Downvote
Thanks - that was what i thought. Problem is that the manufacturer will no longer specify a thermal resistance (Rj-c) due some testing issue so I have no idea how hot the junction will be running, and the case is running close to the maximum junction temperature (within 5-10degC of max. junction spec.)

Been checking all over the net for datasheets and all can I find is the resistance from the die to the legs. The chip has a heat spreader plate integrated on its underside. Ideally I would want the resistances die to spreader plate, die to board via legs and die to case exposed to air to determine the % power exiting through the case and spreader plate where the temp is measured.
 
Upvote 0 Downvote


However, I know that the topside (air exposed) of the case is 10degC hotter than the spreader plate. if I know the power I could estimate the jucntion temperature using this temeperature relationship and assuming the resistance from junction to case is a multiple of the resistance from junction to spreader plate.

Would it be reasonable to assume that the resistance from junction to case is 10x that from junction to spreader plate or more like 100x?
 
Upvote 0 Downvote
If there is really no support available from your supply you should consider measuring junction temperature during operation

Possible for all devices containing at least on pn-junction accessible via the pins.
 
Upvote 0 Downvote
Status
Not open for further replies.

Similar threads

natepiercy
  • Locked
  • Question Question
Service cord vs trailer cable - what's the difference?
Replies
2
Views
317
LionelHutz
LionelHutz
CuriousElectron
  • Locked
  • Question Question
Small solar array vs 12kV distribution line tap for remote site
Replies
3
Views
310
IRstuff
IRstuff
Instrument1352
  • Locked
  • Question Question
Lithium Iron Phosphate (LiFePO4) vs Lead Acid Batteries - Industrial Application & Consideration
2
Replies
38
Views
2K
itsmoked
itsmoked
enverd
  • Locked
  • Question Question
diesel engine vs natural gas engines
Replies
6
Views
379
dpc
dpc
pollacar38
  • Locked
  • Question Question
Static Switch vs Esm Option
Replies
2
Views
226
Noway2
Noway2

Part and Inventory Search

Sponsor

Back
Top