How to decide the Temperature range of an IC??

Question

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 35 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

jw0752 · Answer

Hi Rishi, This chip should have no problem operating where the ambient temperature is 35 degrees C or even in the full sun light though it isn't a good idea to leave it exposed to the direct sun or the rain. If it is protected and the case is in the sun light I would expect ambient temps in the enclosure to rise to as much as 50 degrees C. This should still be acceptable for the operation of the chip but be sure to factor this temperature into your design as other components may drift from nominal values at this temperature. If self heating of the IC is an issue it will likely be covered in the data sheet with specific directions for heat sinking the component. I could find nothing about heat sinking on this IC. John

michaelkellett · Answer

There is no substitute for actual testing. A device left out in full sunlight can get extremely hot (>60C) the link discusses temperatures inside a car: HEAT EXPOSURE IN AN ENCLOSED AUTOMOBILE Your device may be better or worse - and then you must add the temperature rise caused by the operation of the electronics (which you can easily measure.). You should aim never to get closer than 10C away from the maximum junction temperature for the chip you are using (to give yourself a margin for error). You would be unwise to use a 0-70C rated part in this application and you need some testing to be sure that -40 - +85 is OK. MK

dougw · Answer

This can be a complex question - lots of factors to consider as indicated in this article:

Silicon ICs can stand about 150 junction temperature, but their (plastic) package may lose pin seal at lower temperatures due to the difference in coefficient of thermal expansion between plastic and metal, allowing moisture in at the pins. This can dramatically shorten the life of the IC.

If you encapsulate (pot) your circuit to exclude moisture, a 70 C chip may survive higher temperatures, but you may need to be more careful about self heating calculations to avoid junction temperatures above 150 C.

Temperature can affect transistor switching times, so some chips may not work correctly at high temperature even though there is no thermal damage.

If you plan to put your circuit in direct sunlight, try to shade it with a highly reflective cover, as the sun can supply about 1 kW per square meter.

How to decide the Temperature range of an IC??

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