iMX6 Solo - Industrial Grade Temperature testing

[jaiganesh]

Hello all,

We are using iMX6 Solo Industrial Grade Processors in our custom iMX6 board. We have done temperature chamber testing and noticed the following issue

1. When the ambient temperature reaches >75 degree Celcius, the iMX6 processor is turned off with the following messages:

Broadcast message from root@imx6s (Wed Oct  7 13:05:14 2015):

The system is going down for system halt NOW!

thermal thermal_zone0: critical temperature reached(100 C),shutting down

We are not doing much work (simple file copying, ethernet pinging) but still the processor is turned off. It seems the Linux thermal governor for iMX6 is configured for 100C die temperature as 'Critical'.

But my question is, if the processor is marked as Industrial Grade, it should operate at ambient temperature of upto 85C. But it is shutting down at ambient temperature of 75C. It would be great if people from freescale can comment on this

Thanks,

Jai Ganesh

[igorpadykov]

Hi Jai

Linux thermal governor measures die temperature which may differ from

ambient depending on cooling conditions as described in

application Note AN4579 (Rev. 0, 11/2012) "i.MX 6 Series Thermal Management Guidelines"

http://www.freescale.com/files/32bit/doc/app_note/AN4579.pdf

If necessary Linux temperature trip points may be adjusted using driver sources

described in attached Linux Manual Chapter 26 Thermal Driver.

For example trip points of Linux for board with automotive parts may differ from Linux for

consumer parts.

Best regards

igor

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[jaiganesh]

Hello Igor,

Thanks. I looked at the documents and I can understand the dependency between die temperature, ambient temperature and cooling conditions. Is there any document which has relationship between ambient temperature and iMX6 die temperature? (I know it depends on the use case, may be an example table with a particular use case or what is the maximum ambient temperature the iMX6 Solo industrial processor can go under optimal operating and cooling conditions).

And from the document 'http://cache.freescale.com/files/32bit/doc/data_sheet/IMX6DQIEC.pdf ' it seems maximum die temperature for 'commercial extended' as well as 'industrial' grade iMX6 processors is 105C and so, I dont think changing the Critical trip point (which is 100C) for our Industrial Grade is SOM is a good idea (May be if it is Automotive, in which case the maximum die temperature can be 125C, we could have changed that for 120C).

What recommendations would you like to give us for operating the iMX6 SOLO industrial grade processor > 75C ambient temperature.  (May be something like heat spreader or better gating of power/clocks to unused modules)?

Thanks

[igorpadykov]

Hi Jai

p.38 AN4579 shows some simulation results,

p.25 shows Junction to Ambient Thermal Resistance

Thermal resistance - Wikipedia, the free encyclopedia

i.MX6SDL Datasheet Table 7. Thermal Resistance Data

gives RθJA=38 C/W (Single-layer board (1s); natural convection).

http://cache.freescale.com/files/32bit/doc/data_sheet/IMX6SDLIEC.pdf

AN4579 p.49 Software Thermal Management Techniques describes

methods for decreasing power consumption/temperature: right,

it is gating of power/clocks to unused modules and using heat spreaders.

~igor