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I am using a MAX3241E ic in a device that has to run 24x7 out in the open. I am facing a problem deciding the temperature range of the the IC. Since it is out in the open, the ic has to withstand the heat from the sun plus the heating effect due to losses and resistances, etc. I am living in Delhi, India and here the temperature easily reaches 45 degrees. This ic that I have choosen can bear a max temp of 70 degrees. Should I use this ic or should I go for a higher temperature one? Also please tell how should one decide the max temperature of any ic?

Datasheet of the IC: - http://www.mouser.com/ds/2/256/MAX3222E-MAX3246E-99333.pdf

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  • \$\begingroup\$ Additional Question: What is the difference between the IC which can support 0-70°C and the one that support -40-85°C? Do they have the same die? Case material? \$\endgroup\$ – Botnic Jun 30 '16 at 6:24
  • \$\begingroup\$ The wider temperature range is usually Automotive (or military or space qualified) and batch selected to have lower temperature rates leakage currents or closer tolerances and may use slightly more expensive encapsulation. I would use these and check the temperature derating if you expect output shorts. \$\endgroup\$ – KalleMP Jun 30 '16 at 6:54
  • \$\begingroup\$ You will usually find three grades, commercial 0 to +70 degrees (cheap plastic capsules), industrial/automotive -25 to +85 degrees (better qualification and more effort in the bonding inside plastic capsules) and military/aerospace -40 to +125 degrees (full on ceramic capsules). \$\endgroup\$ – winny Jun 30 '16 at 6:57
  • \$\begingroup\$ @Winny: I have rarely seen -25 to 85; -40 to +85 is far more common. \$\endgroup\$ – Peter Smith Jun 30 '16 at 7:35
  • \$\begingroup\$ @PeterSmith You are correct. I got -25 from industrial products, usually where electolytic caps set the lower bar. -40 for the chips inside it though. \$\endgroup\$ – winny Jun 30 '16 at 7:49
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You must select a chip with more than 70°C max temperature.

I can't give you calculation but in my experience a body placed in face of the sun could reach, in summer, 60-80°C, and if the ambient's temperature is so high as you say the heat dissipation is not enough efficient.

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For long life, remember that the minimum temperature you can use for a part is best, so take care mounting and packaging. The part you have chosen will dissipate a watt or more if the design requires it, so the temperature rise associated with the application must be added to the part temperature. In general, the temperature rise can be considered constant, so you can measure the part temperature at ambient and expect the difference between ambient and this temperature to remain the same.

This part should be ok at 35C ambient as long as you are not in a package where the part is not packaged in a manner that creates a "hot spot." Remember that if you have a surface in direct sunlight or on the dashboard of a car, you can approach or exceed 70C. The 70C rating is calculated at a specific (maximum) power rating. But you can always increase expected life by limiting the power the part must dissipate, by limiting the load or duty cycle.

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  • \$\begingroup\$ Well I got the ambient temperature wrong in the question. It is 45 degrees. Now will the ic be ok? \$\endgroup\$ – Rishi Sharma Jul 1 '16 at 5:38

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