CPU overheating sequence

Power discussions, CPU and case temperature
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ddragish
Posts: 3
Joined: Wed Jan 15, 2014 6:02 pm

CPU overheating sequence

Post by ddragish »

If the CPU overheats pass TM1 and TM2 states in a runaway and reaches the absolute critical temp of 120C, Intel states the processor will shutdown and Vcc should be removed in a specified time.
I assume the FITPC2 and BIOS control will remove power from the CPU at this time.
When that occurs and the PC is effectively shutdown, will it:
1. Reset itself immediately and try to power up again? or
2. Reset itself automatically after THEMRTRIP is deasserted and cool down occurs? Or
3. Reset itself automatically after some time delay? Or
4. Stay powered off until power is cycled manually? Or
5. Stay powered off until power button is pushed?
We have an unmonitored unit in the desert of Australia during this heat wave and need to know the power control during an overheating event.
Thank you

mbirger

Re: CPU overheating sequence

Post by mbirger »

The system designed to operate properly under operating conditions defined in system specs, without reaching thermal shutdown.
If you operate the system out of its op. range it will get into throttling states and eventually thermal shutdown.

So, it is better to avoid out of spec op temp ambient, as it may damage other system components (CMOS battery, Storage, Memories).
Anyway, after the ambient will reach allowable temps again or when the CPU will cool down to specific point, it should power up automatically.

In x86 systems (unlike ARM), during S5 low power state (Hibernate/Soft shutdown/Thermal shutdown) most part of the system (except RTC) are off. So when the system exits S5 it starts a proper power up and reset sequence. But I will double check this.

mbirger

Re: CPU overheating sequence

Post by mbirger »

Please let me correct one point -
Thermal shutdown is not S5 state, but a critical shut down.

It is required to disconnect/connect the power supply in order to boot the PC and standard power up sequence begins.

ddragish
Posts: 3
Joined: Wed Jan 15, 2014 6:02 pm

Re: CPU overheating sequence

Post by ddragish »

Ok this is unfortunate for unattended autonomous operation of the unit in the field where it is not accessible to power cycle.

Our unit is an extended temperature unit rated to +70C ambient operation.
In a fanless environment with no natural convection what is the maximum expected temperature delta between ambient and the CPU junction temp with the CPU at full load?

mbirger

Re: CPU overheating sequence

Post by mbirger »

CPU max T_junction = 90 deg.
Intel doesn't disclose any thermal resistance info, but ambient 70 deg will lead to ~80-85 deg on the junction.

Anyway, system has other components (battery, storage, memory) that may suffer when operating out of spec.

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