Thanks for the excellent guidance Matt.
Shawn


On 2013-10-11 9:27 AM, Matt Bennett wrote:
> On Thu, October 10, 2013 2:53 pm, shawn mulligan wrote:
>> Can anyone offer their personal experiences when dealing  with PIC
>> microcontrollers in high-temperature applications -- say, > 170C...
>> Outside of the stated ranges.
>>
>> Specifically, is there a particular device that works for you? Do you
>> consider thermal resistance in your design? Heat-sinking? PCB?
> Many PICs will work well outside the temperature range of the part.
>
> Things to consider:
>
> - rewrite lifetimes go down exponentially with increasing temperature (an=
d
> it's the "not in your favor" kind of exponent).  Avoid flash/eeprom cycle=
s
> when hot.
>
> - Noise in a transistor goes up with temperature- this leads to losing
> analog performance when hot- increase your margins
>
> - leakage in a transistor goes up with temperature, making self heating
> worse- slow your clock down.
>
> - gain margin in a crystal oscillator goes down, so oscillators are more
> likely to not start up or fail. Consider spending extra on a temperature
> rated oscillator as opposed to using a crystal.
>
> - things expand at different rates when hot- parts with leads are popular
>
> - 5V native parts usually have more internal margin. I've seen parts like
> the PIC16C54, PIC16F88, PIC16F887, PIC18Fxxxx, dsPIC30Fxxxx used hot.
>
> - I do not recall seeing people use any of the new enhanced midrange
> PIC16F1xxx at super high temperatures.
>
> - The enhancements that make a part low power (XLP) may not be to your
> advantage when hot.
>
> and... #1 recommendation: TEST, TEST, TEST. If there is a peripheral or
> specification that is important to your application, check it.
>
>
>
> Matt Bennett
> Just outside of Austin, TX
> 30.51,-97.91
>
> The views I express are my own, not that of my employer, a large
> multinational corporation that you are familiar with.

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