AR# 57193

Description

The thermal resistance values for Theta-JA, Theta-JB, and Theta-JC are being updated for the Zynq-7000, Artix-7, Kintex-7, and Virtex-7 family devices. 

For many packages, the thermal resistance numbers will increase, adversely impacting thermal dissipation estimates. 

These incorrect values are also propagated through the Xilinx Power Estimator Spreadsheet (XPE) prior to 2013.3, so customers who leveraged this tool to estimate thermal aspects of power dissipation will be impacted.

Solution

For many 7 Series devices (Artix-7, Kintex-7, Virtex-7, and Zynq-7000 families), the thermal resistance values (Theta-JA, Theta-JB, and Theta-JC) were incorrectly extracted and were documented with inaccurate values. Updated thermal resistance values have been released and are documented starting in version 1.10 of the 7 Series Packaging and Pinout Product Specification User Guide (UG475), version 1.3 of the Zynq-7000 SoC Packaging and Pinout Product Specification User Guide (UG865), the thermal lookup tool (after 8/26/2013): http://www.xilinx.com/cgi-bin/thermal/thermal.pl, and the 2013.3 Xilinx Power Estimator Spreadsheet (XPE).

For customers who leverage thermal resistance values to model the thermal performance of their system, it is recommended that thermal analysis is re-run with the updated thermal resistance numbers.

Customers who analyzed their system with Delphi-format compact thermal models are not required to re-analyze their system, as that model is not impacted by this issue.

Xilinx generates three different thermal models:

1. Detailed 3-D Flotherm model
1. Not generally distributed to customers
2. Validated with thermal measurements
3. Used to validate Delphi and 2-resistor models
   
2. Delphi-format model
1. Distributed to customers
2. No errors in this model for 7 series devices
3. Derived from the Detailed 3-D model
   
3. 2-resistor model
1. Distributed to customers
2. Theta J values published in user guide
3. This model and Theta values are erroneous

Thermal resistance numbers are primarily used to estimate the heat dissipation of a system:

• Theta-JC (JC) measures the heat flow resistance between the die surface and the surface of the package (case). Theta-JC is used primarily in estimating heat dissipation in a system that leverages a heat sink or other method beyond the device package.
• Theta-JA (JA) measures the heat flow resistance between the die surface and ambient. Theta-JA is often used to estimate the junction temperature that will result when estimating the power that an IC will consume in a system with just the IC and a environment specified by JEDEC.
• Theta-JB (JA) measures the heat flow resistance between the die surface and the Printed Circuit Board.  

Revision History
09/12/2013 - Initial release

Linked Answer Records

Master Answer Records