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From: KevinJ93 <kevin_es@whitedigs.com>
Newsgroups: sci.electronics.design
Subject: Re: Operating temperature derating
Date: Thu, 13 Jun 2024 19:02:46 -0700
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On 6/13/24 6:09 PM, Don Y wrote:
> On 6/13/2024 12:42 PM, KevinJ93 wrote:
<...>
> The idea of *carrying* a phone on my person is anathema to me.  So, any 
> time
> I take a phone out of the house, it sits in the car while I run my errands.
> After half an hour, the interior of the car exceeds 130F with certain 
> surfaces
> approaching 160F (seats are ~125F).
> 
> Yet, the phone operates.
> 
> Well beyond max operating *and* storage.  (thus, "margin" -- just no way to
> put an actual figure on it, besides for one exemplar)
> 
>> I've never heard of lower level software being compromised at high 
>> temperatures so basic phone calls would be ok but action video games 
>> would run slower.
> 
> The fact that the phone (and other exemplars) operates outside of its
> "operating range" confirms there is margin in the design.  We know that. > But, no one seems to know *what* this margin is.  (It's not just 
phones but
> almost all consumer kit -- excepting those for which NO operating/storage
> conditions are specified!)
> 
> This suggests that it is NOT a part of the design process but, rather,
> "whatever it is, it is".
> 
> If I tried to make a call and the phone was 160F -- because it sat in my
> car for three hours in the sun -- would it work?  Is there ANYONE at Apple
> who could answer that question?

160F is 71C so the the circuitry I was involved with could be guaranteed 
to work provided the internal temperature of the phone was not 
significantly higher than that 160F.

I believe similar limits would apply to other parts of the phone.

However if the internal temperature had been raised significantly by any 
internal power dissipation then all bets are off.

CPUs are especially challenging as they can dissipate 5-10 Watts at 
extremes - there is no room for anything in the way of heat sinks or 
fans etc. The best they can do is to thermally couple them to the case.

The power amplifiers in the RF section are also significant heat 
generating items.

Your question has a multi-dimensional answer, it depends upon a host of 
other things including the recent usage of the phone.

A phone could be designed to guarantee operation at the temperatures you 
state but that phone would certainly cost more, be physically larger, 
heavier etc. The current specifications have been accepted as adequate 
by the majority of customers. Probably there do exist ones with extended 
environmental specs for specialized applications such as the military 
where that is more important than cost, weight, size etc.

If you want to improve the likelihood that your phone works when you 
need it - don't leave it lying in sun. Even in a hot car some places are 
cooler than others.

<...>
> 
>>> We expect cars to continue to operate in those temperatures.  What's the
>>> criteria that we use to determine what should and shouldn't be expected
>>> to remain operational?
>>
>> Automotive devices that expect to be in the engine compartment are 
>> designed for -40C to +125C or +150C.
> 
> The devices I mentioned are located in the *passenger* compartment.
> What value an engine compartment that can't be *controlled* by devices
> in the passenger compartment?  :>

I've also worked in some aspects of automobile design and there were 
multiple environmental zones defined - the cabin being the most benign.

Probably parts there are specified to 105C. Although it can get pretty 
toasty at the top of the dashboard.

> Will the GPS operate when the vehicle's interior reaches 160F?  What about
> the roadside assistance feature?  Backup camera?  Will the electronics that
> govern the cycling of the air conditioning compressor function?  Do you 
> recall
> ever hearing someone complain of the electronics in their vehicles NOT 
> working
> when they returned to their parked vehicle after work?  ("margin")

The temperature is not uniform in the car and often electronics are 
placed in areas where they won't reach the high temperatures you mention 
- in some of my cars for example the electronics were under the seats or 
behind the glovebox.

> The fact that the car manufacturers recognized these some devices WOULD 
> fail
> (and added a variety of idiot lights on the dash to signify those failures)
> suggests they either couldn't make them operate over these extremes *or*
> couldn't AFFORD to make them operate over these extremes.
> 
> But, as a buyer looking to drop $50+K on a vehicle, what assurances do
> you have that those systems (for which you are paying additional monies)
> WILL operate when you are the vehicle's owner?  If they won't operate
> when the vehicle is sitting on the *dealer's* lot, will they operate when
> the vehicle is sitting in the grocery store's lot?  Your employer's lot?
> Your driveway?  On the highway?  (etc)

Modern cars are impressively reliable but they may not be guaranteed to 
operate over the full gamut of environmental conditions and usage. They 
just have meet the great majority of the customers' expectations.

> Vendors seem to treat *consumers* as ignorant dweebs; the same sorts of
> hand-waving wouldn't be tolerated by an industrial/commercial customer!
>

The market decides. Price is a dominant factor in vehicle sales.

kw