Not accurate temperature readings on iMX6ULL Evaluation Kit

[alex06]

Hello,

I did some temperature testing of the NXP Evaluation Kit for iMX6ULL, using your provided Linux BSP :

Temperature Tested : - Room temperature : 24°C

                                    - CPU - idle surface readings: 33.5°C ;

                                    - SOC temperature - idle mode: 47°C;

                                    - Power consumption of the CPU : 0.464 V;

Can you tell me why is this big difference between the CPU - idle surface readings and the SOC temperature - idle mode (Delta: 13°C) and if the SOC temperature - idle mode readings are correct, why is the SOC temperature so high (47°C) if the power usage is just 0.464V?   

Thanks

Alex

[igorpadykov]

Hi Alex

for temperature measurements one can check

AN4579 i.MX 6 Series Thermal Management Guidelines

https://www.nxp.com/docs/en/application-note/AN4579.pdf 

Best regards
igor
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[alex06]

Hi Igor,

I measured the top case of the CPU using a FLIR thermometer and I had, in idle mode, this value 33.5°C.

I measured the SOC temperature using this command "cat /sys/devices/virtual/thermal/thermal_zone0/temp" and I had, in idle mode, and I had this value 47°C.

The CPU power consumption, in idle mode, is 0.464W.

Why is this temperature difference, if in the AN4579 i.MX 6 Series Thermal Management Guidelines - i.MX 6Dual/6Quad Thermal Characteristics, the Junction to Case (Top) value is 1°C/W??

Thank you.