Sink Question (Little difficult)

[dark]

Hi

I have an FPGA with Theta JA=80DegreeC . At 85 degrees Ambient it is sinked with a sink coeff of 10DegreesC/W . I want to know how much cooling this sink is providing to the Junction.

Thanks

PS; power input is 1W maximum to the chip when designing.

 

[Ubergeek63]

you need the junction to case number.

junction to ambient is meaningless when you are putting on a heat sink.

if the package is not designed to use a heat sink, it borders on useless to put one on.

junction temp at 85C with 1W dissipation at 80C J-A gives you a chip blowing 165C

Dan

 

[user_88]

This document might be useful ...
https://www.electro-tech-online.com/custompdfs/2009/01/Pack_Therm_AN.pdf

If not, please restate your question ....
Need to know the parameters that you have, and what you are trying to determine.
also please be more careful with the units .... easier to understand the problem.

 

[dark]

I provide more details ;
Tjc=22C/W
Tja=80C/W

If I provide a sink with coeff of 11C/W . How much the Junction will be lowered at 85C ambient . I can reduce the power to about 0.7W no less than that . What I want to know is how much temperature releif the sik will provide . Thanks for Actel link .

I know Dan the chip will work at 165C but it wont fry , it has built in compensation to reduce the supply and certain other things , but I dont want to operate at that temp . You say if its not mentioned to sink the chip then one shouldnt do that , BUT half of the industry runs this way and is successfull! . I dont have an option(due to power constraint) but people provide peltier sinks to achieve one.

Thanks

 

[Ubergeek63]

I provide more details ;
Tjc=22C/W
Tja=80C/W

If I provide a sink with coeff of 11C/W . How much the Junction will be lowered at 85C ambient . I can reduce the power to about 0.7W no less than that . What I want to know is how much temperature releif the sik will provide . Thanks for Actel link .

I know Dan the chip will work at 165C but it wont fry , it has built in compensation to reduce the supply and certain other things , but I dont want to operate at that temp . You say if its not mentioned to sink the chip then one shouldnt do that , BUT half of the industry runs this way and is successfull! . I dont have an option(due to power constraint) but people provide peltier sinks to achieve one.

Thanks

Silicon chips are normally 125C junction. If it is thermally protecting itself it is shutting down and not running.

Normally all you do is add the thermal resistances, multiply by the wattage, and add to the ambient. (22+11+1(guessing, it depends on how good the interface from the pad to the sink is, and I am assuming you have a sink pad since it gives a junction to case))*1W+85C=119C dangerously close to 125C but doable.

For a peltier you are looking at your power plus the peltier power going into the heat sink. you are probably talking about 4W going into the heat sink for 44+85=129C at the peltier. if you get one that will get you 40C down you are at 90C. either way you need a better heat sink or a big peltier.

Dan

 

[dark]

Silicon chips are normally 125C junction. If it is thermally protecting itself it is shutting down and not running.

Normally all you do is add the thermal resistances, multiply by the wattage, and add to the ambient. (22+11+1(guessing, it depends on how good the interface from the pad to the sink is, and I am assuming you have a sink pad since it gives a junction to case))*1W+85C=119C dangerously close to 125C but doable.

For a peltier you are looking at your power plus the peltier power going into the heat sink. you are probably talking about 4W going into the heat sink for 44+85=129C at the peltier. if you get one that will get you 40C down you are at 90C. either way you need a better heat sink or a big peltier.

Dan

That means uncompensated it was 165C and when sinked 119C . What temp my sink is at is it 131? , or am I missing the point .

Thanks for the time

 

[dark]

if the package is not designed to use a heat sink, it borders on useless to put one on.

Dan

Dan , you seems to be hitting some point for a chip that hase an entire plastic mould and no provision for heat outlet copper slug etc , to attach a sink.
Please help me with can we mount a sink to a regular package (SOIC wide) and get some resultes might be few degrees will be ok , or it is a dangerous idea. But sinks Theta-sa is surely going to put down the thermal resistance or it would be a waste.

Thanks
-Adi