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Visitor
Visitor
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Registered: ‎04-02-2019

XC2C256-7VQ100I Thermal Resistances

I couldn't figure out where to post this, so my apologies if this isn't the correct place.

I'm looking to use XC2C256-7VQ100I in a design but I'm having an issue in cooling it. I am now looking into top-cooling the part, but could not find the junction-to-case (top) thermal resistance (in °C/W) in order to do so. Could someone please provide that for me?

Additionally, I would like to verify that the junction-to-case (bottom) thermal resistance is indeed the 10.9 °C/W that is listed on the datasheet. Thank you in advance!

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Xilinx Employee
Xilinx Employee
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Registered: ‎08-10-2007

You can find device specific thermal data here: https://www.xilinx.com/cgi-bin/thermal/thermal.pl

This thermal query tool allows you to choose your device / package combination and see the resulting thermal data.

For the XC2C256-VQ100 part, the following information is provided:

Thermal data summary for XC2C256-VQ100

Device Family : CoolRunner-II
Device Name : XC2C256
Package Name : VQ100
Unit : C/Watt
   
JA (Still Air) 42.9
JA (250 LFM) 35.6
JA (500 LFM) 33.2
JA (750 LFM) 32.3
JC 10.8
   
LFM = Linear Feet per Min
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Registered: ‎09-17-2018

A reasonable and useful rule of thumb is half the power is conducted out the top (with a heatsink and airflow),

And half is conducted out into the pcb through the bottom of the package.

The power estimation spreadsheet is a useful tool to see how much cooling you need.

l.e.o.

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Visitor
Visitor
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Registered: ‎04-02-2019

I understand getting these values from the tool, but what I want to do is interpret it. If I want to top-cool this component to a heat sink but only rely on conductionnot blowing air over it as well, I need to be able to understand how much power will want to go up to the heat sink versus down into the board. Is the Theta JC value provided representing the top part of the case (and thus for the top-cooling part) or for the bottom of the case (for the heat going into the PWB)? Since this is not a BGA part that normally gets top-cooled I do not want to just assume X% amount of power goes in each direction.

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Xilinx Employee
Xilinx Employee
648 Views
Registered: ‎08-25-2010

Hi @mturley

Theta JC is used for device/package comparison purposes only according to JEDEC four-layer board. And this value is different than the one in your actual board conditions and enviroment. A system-level thermal simulation can help interpret it.

Thanks
Simon
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