AR# 38636


11.1-12.3 XPower Analyzer (XPA) - Overestimates Device Junction Temperature


My junction temperature reported from XPA looks higher than it should be, why is this?


XPA overestimates the junction temperature in software versions 11.1 through 12.3. This applies to any supported device, however, itmostly effects designs with significant off-chip power. Board terminations for output and bidirectional output I/Os are the primary source of off-chip power. Therefore, designs with high-speed memory interfaces (e.g., using HSTLandSSTL I/O standards) would be most affected.

The estimated power is calculated correctly, but the junction temperature is overestimated. This is fixed in 12.4, or the following can be performed as a work-around:
  1. Manually calculate the junction temperature by using the following equation:
    Junction_Temperature = Ambient_Temperature + (Effective_ThetaJA * Total_On-Chip_Power)
  2. Use XPA in batch mode which generates an ".xpe" file to use with the XPower Estimator (XPE) spreadsheets.
    • First, generate an ".xpe" file from XPA by running xpwr command line using the '-xpe <filename>' switch.
    • Second, open XPE and click the 'import' button to load the previously generated ".xpe" file.
    • Third, review the imported data and complete the spreadsheet as necessary before using the junction temperature listed on the 'summary' sheet.

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AR# 38636
Date 12/15/2012
Status Active
Type General Article
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