[EFM] EFM Extended Temperature Range
> Tom & fellow EFMers:
> During the meeting last week, I took an action item to do some research on the (extended) temp range for
> an EFM system and report back. Although I am still waiting for some additional info of how Nortel
> resolves the case temperature vs ambient temp with our optical component suppliers, I pass along the
> following information from one of our authorities on the subject who has designed and built both copper
> and optical access modules.
"The figure of -40 to +85 can be excessive or inadequate. The low end is set by northern winter climates,
at night (therefore without sun loading) and an EXTERIOR temperature of below -40 can be fairly regularly
observed, but interior heating of the equipment may lift this requirement somewhat.
The high-end requirement is established by taking into account the maximum summer free air EXTERIOR
temperature (say +50 deg C alongside an Arizona desert black flat-top highway) and adding self-heating
(which is a function of the design of the equipment) and the effects of sun loading at ~ 1.6 kW per square
meter, the effects of which are dependent on the design and colour of the housing.
Regarding Tom's note on semiconductor temp ranges, I was at National Semi when we first started designing
and specifying IC's for the automotive environment. Much of the testing methodology for testing for
automotive was drawn from National's experience selling to the telephony market including Nortel.
> "While National Semiconductor says:
> In general, the temperature ranges are defined as follows:
> Military: -55 to +125'C
> Industrial -40 to +85'C (some variation, check datasheet)
> Commercial 0 to +70'C
> Automotive -40 to +125'C (some variation, check datasheet)
> Note that in this case, even the specification indicates that it is not
> definitive!"
The automotive application had two temp ranges, -40 to +125'C for under the hood and -40 to +85'C for all
other.
The variations noted are key and one must read the fine print on the datasheet. Some parametric limits in
the datasheet may only be guaranteed at 25' C usually due to testing limitations. Also the components may
not be 100% tested at those limits for economic reasons. Also note that these semiconductors are all
specified at ambient. In many cases the datasheet will provide a derating curve for temperature variants.
Details on optical components to follow.
Richard Brand
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