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From: Don Y <blockedofcourse@foo.invalid>
Newsgroups: sci.electronics.design
Subject: Re: Operating temperature derating
Date: Thu, 13 Jun 2024 18:09:45 -0700
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On 6/13/2024 12:42 PM, KevinJ93 wrote:
> On 6/12/24 12:26 PM, Don Y wrote:
> <...>
>> It's been above 100F (38C) for 16 days, already.  People are still working
>> their normal outdoor jobs, looking at cars on dealer lots, walking 100 yards
>> across uncovered parking lots to gain entry to stores, etc.
>>
>> Are phones NOT expected to work in these environments?  (Gee, I wanted to
>> telephone emergency services to get help for my buddy who collapsed in
>> the heat but it was too hot for my phone to make the call)
> 
> The phones may not stop working but may not meet performance specifications. 
> For example applications may not work as fast as at lower temperatures.

But, "applications may not work as fast" if multiple applications are running
or if you've installed some "service" that competes for resources.  Where's
the disclaimer about that?

And, what's the caveat when the phone is being *operated* at a temperature
that exceeds its *storage* temperature?  It's been hotter than 113 (iPhone
storage max) several times, here, already -- and summer doesn't officially
start for another week or so.

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?

My $40K electric wheelchair tells me to recharge the batteries in a certain
temperature range.  But, doesn't tell me in what range of temperatures I can
OPERATE that chair!  Surely this is important -- whether I live in Alaska or
Florida -- as a chair that won't move would leave me stranded!

I know I can operate (and "store" when not actively being operated) TVs on
the back porch despite the fact that the ambient climbs to well above 110.
Yet, the TVs don't tell me that this is possible.

> The ASICs I worked on had a -25C to +75C operating range. When the CPU was idle 
> the phone would be too hot to hold if the internals were at 75C.

Of course you don't need to hold a phone to use it.  My blind friends use
the voice interfaces to their phones (ear buds) -- leaving them in a fanny-pack
(or purse) so they can have their hands free for walking canes.  That seems to
be increasingly common.

The fact that you design components for a 75C range suggests you expect the
phone's interior (at the die level) to approach that temperature.  You
didn't, for example, design for 50C (and, in those sorts of volumes, you can
pick whatever point on the process/price/performance curve best suits your
needs/requirements instead of being constrained to "standard products")

>> 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?  :>

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 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)

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