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I have noticed that a lot of smart phones say that they won't operate under -4 degrees F (-20 degrees C). Can anyone explain to me what happens when the phones get cold that stops them from operating?

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  • \$\begingroup\$ Here's another question that is little bit related. - Might be somewhat interesting for you. \$\endgroup\$ – Harry Svensson Dec 28 '17 at 23:17
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    \$\begingroup\$ The first smartphone I used had its LCD become solid at -3°C \$\endgroup\$ – PlasmaHH Dec 29 '17 at 23:08
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    \$\begingroup\$ Batteries become chemically inactive in the cold. Heat them, or get a crank and use yourself as a power source. Seriously, this can be mitigated just by having the device in your inner coat pocket. \$\endgroup\$ – user2497 Dec 30 '17 at 14:55
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-4 F is -20C, which is a standard low limit for chips and electrical components. Some of that is just because it is very hard to test chips at low temperature, but there are real issues you can run into, which include:

  • Batteries degrade at low temperatures, depending on their chemistry.

    • The battery output voltage is lower, meaning you need more current to get the same power

    • The battery internal resistance can increase. The added resistance can heat up the board, but it also wastes power and makes the battery output voltage less stable, as it will change with current draw.

    • The heat caused by the extra resistance can potentially damage the battery, since you are heating up the inside while the outside is cold, creating a thermal gradient which adds mechanical stress.

  • Thermal cycling of parts can become worse. Things break when you make them cold and heat them up because of thermal expansion. I believe this issue is worse at lower temperatures, possible related to metals becoming brittle when they are very cold.

  • Chips can draw more current at low temperatures. This issue compounds the other two, since more current becomes more heat, which increasing thermal cycling.

  • Chip timing changes. Digital circuits have special timing rules to ensure that all signals are in the right place at the right time. Lowering the temperature changes all that and can create a race condition.

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    \$\begingroup\$ I am disappointed when the chip doesn't work while I single-step the clock. \$\endgroup\$ – Joshua Dec 29 '17 at 2:52
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    \$\begingroup\$ The battery point's a little confusing... since "they will get hotter as you draw more current" so wouldn't that solve the low temperature problem? \$\endgroup\$ – Xen2050 Dec 29 '17 at 7:33
  • \$\begingroup\$ @Xen2050 the battery heating (or the chips heating) may self-protect the entire device if the enclosure the device is in is relatively well insulated - as in, it may have taken days to get down to such a low temp, and after the cold-start period the device may warm up enough to keep itself within operating temp \$\endgroup\$ – KyranF Dec 29 '17 at 14:51
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    \$\begingroup\$ @Xen2050 KyranF is right, the system will eventually warm up, but there are related issues of wasted power (that heat has to come from somewhere) and, potentially, a temperature gradient is not the best thing, because of mechanical issues. No designer should say "let's warm this board up by heating the inside of our battery". I will clarify my original answer. \$\endgroup\$ – pscheidler Dec 29 '17 at 14:56
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    \$\begingroup\$ "I am disappointed when the chip doesn't work while I single-step the clock." There are two type of timing error in a digital circuits: set-up timing error and hold timing error. The latter is independent of the clock frequency so it will fail on single stepping too. \$\endgroup\$ – Oldfart Dec 29 '17 at 17:24
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For most of these devices it's the display...

LCDs don't like the cold.

Typically, standard LCD character and graphics modules provide a temperature range of 0°C to +50°C. However, several display manufacturers offer extreme temperature models with operating temperatures of -40°C to +80 or +85°C. There also is a wide selection of standard versions that range from -20°C to +70°

Source

The newer OLED types do have a much better temperature tolerance though, -40°C to +80°C.

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  • \$\begingroup\$ In my experience with laptop LCDs in the cold (around -10°C) the picture gets grainy and slow but it still works. There are rugged laptops with heated displays to work around this problem. Some smartphones have OLED displays, do they have the same issues? \$\endgroup\$ – Michael Dec 29 '17 at 8:54
  • \$\begingroup\$ @Michael OLEDs do have a wider temp range since there is no fluid to thicken or freeze. " -40°C to +80°C. " OLEDs do have other issues though. \$\endgroup\$ – Trevor_G Dec 29 '17 at 13:54
  • \$\begingroup\$ As a card-carrying Canadian, I can verify that the LCDs in my car dashboard work just fine at -20°C. \$\endgroup\$ – Spehro Pefhany Dec 31 '17 at 7:24
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    \$\begingroup\$ @SpehroPefhany hey fellow Hoser, as my answer states, some can be made to work at -40C, but automotive parts and cheap phone parts are not in the same class. The heat generated from the backlight helps a lot to keep the liquid fluid too. If you let them freeze they can and will crack though. \$\endgroup\$ – Trevor_G Dec 31 '17 at 13:35
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Batteries dislike cold.

Generally all batteries lose capacity and current in the very cold. (However, using them often warms them up.). Lithiums have a particular problem with being charged in the very cold.

Also, devices are concerned about condensation occurring inside the device from humid air entering the headphone jack etc.

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Crystal oscillators may not start up; or the crystal resonant frequency, which has a temperature coefficient, may be outside the guaranteed Automatic Frequency Control (afc) range, needed to ensure the data packets start on expected time slots even after some hours of operation and phase slipping.

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To add my 2 cents on all the great answers (which would apply not only to electronic devices but generally all electric devices) - the temperature drop results in change of material resistance (namely for metals they become less resistant), while this might seem a minor thing, in industrial equipment this is one of the items accounted for. Electronic devices would suffer most at that because many microchips rely on resistors between some of their lines to be of specific value, if that value changes the microchip may start misbehaving or completely shutdown.

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Analog circuits can also have problems at low temperatures. Resistance changes across temperature, and so do transistor threshold voltages and transconductances. If a reference voltage or current goes out of spec, it can affect other analog circuits that depend on it (like an ADC or a charge pump).

When you're simulating a design and (later) characterizing and testing hardware, you have to pick a lower bound for temperature. There may not be any actual problems if you go a little below that temperature, but the manufacturer can only guarantee correct operation if you stay within the tested limits.

That being said, for smartphones the battery and display are probably the bigger concerns, as the other answers show.

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When you get into minus figures things start to slow down, there is something called ABSOLUTE ZERO which is 0 degrees Kelvin or minus 273 C. @ 0 Kelvin nothing moves, including protons and electrons, it basically freezes electricity (not sure what happens with photons). Eventually chip speeds will slow down but not at the same rate so the sync is lost.

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  • \$\begingroup\$ that should be -273 Cent, 0 K, or -460 Farenheit, or 0 Rankin. \$\endgroup\$ – analogsystemsrf Jan 3 '18 at 2:06
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My 2 cents is that there is a "Diode Equation" (google it!) that includes current, voltage and temperature. So a semiconductors behaviour depends on temperature. Useful in a digital thermometer, but must be counteracted by adding trace elements and other magic by the manufacturers of ordinary chips to make them work "straight". But this works only within a limited temp. range depending on budget and usage. So I guess it would be possible to make a phone that works well only between -220C and -150C, for example.

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