08-18-2019 01:03 AM
I designed a kintex7 325t custom board and I am working with it. for one of my projects, I calculated power of the board with Xilinx Power Estimator and after importing all parameters, Total On-Chip Power shows 8.249W and Junction Temperature 40.6 degrees Celsius. After that I wrote my VHDL code and the Vivado report summary shows 7.197W for Total On-Chip Power and 38.6 degrees Celsius for Junction Temperature which is near to Power Estimator report. When I programm my FPGA the temperature will go near 90 degrees Celsius and I am suprised. First I thought my current is more than what Power Estimator says and I had to measure. After measurement, I saw the current and power is like Power Estimator and Vivado Summary report.
Now I don't know how it is possible. Is this possible to be for power sequencing? My power sequence is:
If this problem is not for sequence, can you help me and tell me what can be the reason?
Thank you very much
08-19-2019 01:34 AM
Assuming the power dissipation is correct, that sort of temperature would only be possible in still air with no heatsink.
Did you remember the heatsink and the fan?
The screenshot shows that the tool thinks that the effective thermal resistance is 1.9K/W, which also implies that you need a (modest) heatsink and a fan. (The screenshot shows a 250 LFM airflow.)
08-19-2019 03:09 AM
Thanks for your reply. I have a heat sink but I don't know what is its thermal resistance. The dimension of my heatsink is about 80mm*52mm. So you say if I don't place fan and heat sink, then FPGA temp may goes to 90 degrees Celsius?
08-19-2019 03:30 AM
Probably. Without a fan you have natural conduction, airflow is driven by the heat itself.
There is more to heatsinking than sticking a heatsink. thermal grease and proper attachment are essential even if they look like a detail. Last but not least, there are limitations on the pressure you can apply to a heatsink on a package. I remember some document about that.
Note as well you have selected 250 LFM airflow, more than 4 litre per second, that is a medium power fan, PC type I guess.
Last curiosity is why do you want it that cool? You can bear with some 70C on the silicon.