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AR# 63016

Vivado Power Analysis - How do I set thermal information (Process, Junction Temperature, and Environment Settings)?


How do I set thermal information (Process, Junction Temperature, and Environment Settings)?


Ideally Static Power is the sum of source to drain and gate leakage power in the transistor.

The static power entirely depends on Thermal conditions.

Providing more accurate thermal information is the basic requirement for accurate Power estimation.

Process Corner:
When a device is fabricated, it is very possible that each device will have variations in performance and power consumption, due to the manufacturing process.

Report_power offers the static power estimation for two process corners: TYPICAL and MAXIMUM.

Ideally all devices should meet TYPICAL estimation value.

However, due to process variations and distribution of devices, some devices may be closer to MAXIMUM. 

The MAXIMUM setting guarantees that the reported numbers are within operating range and closer to hardware measurements.
At a fixed Junction Temperature, the expected variation in static power from TYPICAL to MAXIMUM would be ~2.5X on Commercial devices.

***RECOMMENDATION*** Use MAXIMUM Process settings to achieve worst-case static power accuracy.

In Vivado, the default Process is 'Typical' in Report_Power. 

This can be changed either in the Report_power GUI settings window or through the following command in the Tcl Command Line:
set_operating_conditions -process maximum

Junction Temperature:
Leakage current increases exponentially with Junction Temperature which results in higher Static Power.

Junction Temperature depends on various factors: the total power of the device, the cooling system, board selection and ambience.

By default the Junction Temperature is computed based on other Thermal setup inputs: Ambient Temperature, Heat Sink, Board Selection, etc.

Since it is directly proportional to Total Power, it varies when dynamic Power increases.

It is very important to specify the correct Junction Temperature to estimate accurate Static Power.

***RECOMMENDATION*** Read the Junction Temperature at the time when power is measured on hardware and overwrite it in Report Power Settings.

To set Junction Temperature in Vivado GUI, enable the 'Junction Temperature' check box in Report_power setting window and enter the values.

Alternatively you can use the following TCL Command:

set_operating_conditions -junction_temp 45
You can measure approximate Junction Temperature by placing a simple thermistor or other hand-help temperature measurement devices on the Xilinx device.
If one of the Xilinx Hardware Programing tools is used to program the devices, then you can read the Die Temperature values.
For example, In ISE-Impact you can read Die Temperature values through the Menu (Debug->Read Status Register).
The Vivado Hardware Manager graphically drafts the Die Temperature plots in the System Monitor Window.

Note: Refer to UG907 Power Analysis & Optimization for more information about Tcl command usage and signal rate or toggle rate usage.

Linked Answer Records

Master Answer Records

Answer Number Answer Title Version Found Version Resolved
63015 Vivado Power Analysis - How do I get the most accurate results from report_power? N/A N/A
AR# 63016
Date 12/04/2014
Status Active
Type General Article
  • Vivado Design Suite - 2014.4
  • Vivado Design Suite - 2014.3
  • Vivado Design Suite - 2014.2
  • Vivado Design Suite - 2014.1
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