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AR# 55291

XPE 14.x - Calculated Theta JA does not seem correct using custom Board selection


While using custom Board selection, XPE calculated junction temperature is much lower than board temperature, and calculated Theta JA does not seem correct.


When using custom Board settings in XPE, calculated junction temperature is much lower than board temperature and Theta JA drops (0.1 - 0.6 C/W for this case when board temperature varied between 85 -125 deg C). 

Environment settings:

Ambient temperature = 85 deg C

Airflow = 0 LFM 

Theta JB = 2.0 deg C/W

Board temperature = 125 deg C. 

As a workaround, add a custom heat sink to the spreadsheet to fix the issue. For this specific package, that is Theta JA = 6.1 C/W in still air.


In general, using a custom Theta SA with airflow should calculate package Theta JA close to the same, as there is no heat sink in the above setup.

AR# 55291
Date Created 04/01/2013
Last Updated 08/05/2013
Status Active
Type General Article
  • Virtex-7
  • ISE Design Suite - 14