Answers Database

PACKAGES: Information on calculating Temperature/Thermal Characteristics(Theta-JA)


Record #1226

Product Family:  Documentation

Product Line:  Data Book

Problem Title:
PACKAGES: Information on calculating Temperature/Thermal
Characteristics(Theta-JA)



Problem Description:
Urgency: Standard

Keywords: thermal, theta, ja

General Description:
This is a brief summary on determining the thermal characteristics of a Xilinx P
art.  A more detailed discussion of thermal characterization can be found in the
 chapter called "Packages and Thermal Characteristics"
usually located in the last sections of the data book.


Solution 1:

Theta-JA (junction-to-ambient heat resistance) is used to calculate the die temp
erature, which should not exceed the maximum temperature rating for a particular
 device.  Theta-JA is the increase in temperature that a device will experience,
 relative to the ambient temperature, over the amount of power dissipated by the
 device (degrees Celsius per watt).  In short, the following equation must hold:


   Ta + P*Theta-JA < Tj

where Ta is ambient temperature, P is the power dissipated by the device, and Tj
 is the maximum temperature rating for the device (85C commercial, 100C industri
al, Tc=125C for military).

We measure Theta-JA in four different situations:

     0 LPM (still air)
   250 LPM (air flow of 250 linear feet per minute)
   500 LPM (  "  "  "	500   "  "  "  "  "  "	" )
   750 LPM (  "  "  "	750   "  "  "  "  "  "	" )

You can therefore use the measurement or measurements that fit your particular s
ituation.

Note:  For most devices the temperature range for Military
grade devices (M and B) is the case temperature not the
junction temperature.  For further information on a
partitcular device please check the Xilinx Programmable
Logic Databook.



End of Record #1226