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HDC1008: HDC1008 - dynamic offset temperature compensation

Part Number: HDC1008
Other Parts Discussed in Thread: HDC2080

Hi,

we use the HDC1008 sensor in an embedded device (A20 Allwinner, display, housing) .... 
Due to heating effects in the device we need to use some sort of temperature compensation  .... The heating due to display-backlight and mechanical design may be considered as constant as soon as the device is in operation for some time and the temperature inside the housing is more or less stable ....
Our problem is the heating effect due to dynamic load on the A20 processor (depends on application, user interaction, ....) and we are not sure how to handle this the best way....
Our current approch is to use the current measurement of the AXP209 powerchip used for power supply to calculate a dynamic temperature offset somehow.... another possibility may be to use an averaged cpu-load to calculate the offset .....

The question is, since this should be a common problem on many different embedded devices:
Is there a common approach to handle this use case? Maybe there already exist a formula/algorithm to calculate the offset depending on some sort of current measurement or cpu-load?

Best regards,
Bernhard

  • Hi Bernhard,

    From my understanding the problem is isolating the heating from the A20 processor from the constant temperature from the "display-backlight and mechanical design"? 

    Please see the below app note for design considerations and layout techniques for different applications.   

    http://www.ti.com/lit/an/snoa967a/snoa967a.pdf

    Thanks,

  • Hi David!

    Thanks for the quick response - and in our product the hardware-designer already implemented similar  approaches as mentioned in your design guidelines to reduce the effects of processor heating ....
    But nevertheless, the PCB is in a small housing and we can't eliminate the heating effects completely ....

    Some of our customers run applications on the device with very low cpu load, other customers run applications pushing even the gpu to the limit .... and therefore we need some software approach (additional to the hardware guidelines) to compensate the heating effects of the A20....

    One approach would be to measure the current (e.g. high gpu-load generates high current) and calculate a dynamic temperature offset ... but at this point we are not sure how to handle this the best way ....

    Best regards, 
    Bernhard

  • Bernhard - 

    Perhaps one way forward here is to show us exactly the mechanical drawing or a picture of what has been implemented. In addition to the app note David pointed out, there is also a similar one that was put together for the HDC1x and 2x devices specifically. 

    http://www.ti.com/lit/an/snaa297a/snaa297a.pdf

    Another way forward would be to characterize the unwanted heat rise / or adder and then use a device like the HDC2080, which does have offset register for temp (and also one for %RH) that can be used to give you a value which has been already offset from measured. 

     

  • Hi Josh, David!

    I think the way to go is to characterize the unwanted heat rise somehow ....but I think that we need to develop our own formula for the compensation ....

    I hoped that maybe there already exist an algorithm / pseudocode / library so that we can input the actual current together with some additional parameters (modelizing the system) and the algorithm calculates the current temperature offset somehow....

    But many thanks for your advice!

    Best regards, Bernhard