How Do I Plan to Power My FPGA?

Xilinx Training

Objectives

After completing this module, you will be able to: Explain how static power is different from dynamic power Describe the impact a smaller device geometry has on static power consumption Define the relationship between leakage current and junction temperature Describe some of the device data sheet information that pertains to power consumption

Total Power = Static + Dynamic

Once the device has powered up, there are two main components to power consumption Static power

• Primarily transistor leakage current  Source to Drain leakage IS →D

source

 Gate to substrate leakage IGATE • Some current from special circuits (DCM, etc)

gate I GATE I S



D drain Dynamic power

• Switching in the FPGA core and I/O • Determined by CV 2 f  node capacitance,  supply voltage  switching frequency Buf

C

Buf

The Industry Trend in Leakage Current

New Technologies



Smaller transistor length



Higher IS →D Faster transistors (lower Vt )



Smaller Gate Oxide thickness



Higher (IGATE) The total leakage for all transistors in the device

– ICCINTQ = IS →D + IGATE

Even when the device is not doing a task it still draws some power

– This leads to the development of new features such as Suspend and Hibernate mode

Smaller process geometries lead to higher static power

100 0 100 10 1

Transistor I Trend

Low V T leakage

Regular V

T 0.1

220 180 150 130 90 75 Technology Node 65

Properties of Leakage Current

Leakage Current Junction Temperature (T J ° C) 25 50 85 100 Normalized I CCINTQ Typical 1.00

1.46

2.50

3.14

25 °C 50 °C 85 °C 100 °C

I

CCINTQ



-40 -20 0 20 40 60 Junction Temp °C 80 100 120 140

Leakage current increases dramatically with Junction Temperature

Data Sheet Specifications Iccintq, Iccoq, Iccauxq

– These are the bare minimum your power supply to operate the device – Does not guarantee that your design is going to work, just that this is the minimum current – Dynamic power requirements will increase the required current during operation currents (quiescent) required for – Refer to the Spartan-6 FPGA Data Sheet or the Virtex-6 FPGA Data Sheet

Data Sheet Specifications Power-On requirements are greater than the operating current requirements

– These are the bare minimum – currents (quiescent) required for your power supply to power up the device This is used for picking out a sufficient power supply – Does not guarantee that your design is going to work, just that the device will configure – Refer to the Spartan-6 FPGA Data Sheet or the Virtex-6 FPGA Data Sheet

Design-Dependent Power

It is up to the user to plan on how much current their system can use

– This is dependent on the design, FPGA, and other devices used in your system

It is also up to you to anticipate how much your worst case power consumption might be

– Xilinx provides descriptions of the current draw your FPGA might have at power-up, during minimal operation, but not for worst-case conditions

• Too much is design dependent (resources used, clock frequency, etc.)

To get the best power estimate we offer a couple of power estimation tools

– Please refer to the

Power Estimation Video

for more information

Estimating Power Consumption

Power calculations can be performed at three distinct phases of the design cycle

– Concept phase: A rough estimate of power can be calculated based on estimates of logic capacity and activity rates • Use the Xilinx Power Estimator spreadsheet – Design phase: Power can be calculated more accurately based on detailed information about how the design is implemented in the FPGA • Use the XPower Analyzer – System Integration phase: Power is calculated in a lab environment • Use actual instrumentation

Accurate power calculation at an early stage in the design cycle will result in fewer problems later

Summary

Static power is dependent on the transistor leakage current Dynamic power is dependent on the switching of the logic in the CLB array and IOB resources Smaller device geometry increases the static power consumption of all devices

– Newer devices have a higher static power consumption

An increase in junction temperature dramatically increases the leakage current and your static power The minimum current required to operate and configure the FPGA is provided in your FPGAs data sheet

– But the best way to estimate your power consumption is with either the Xilinx Power Estimator spreadsheet or the XPower Analyzer utility

Where Can I Learn More?

–

Xilinx online documents

•

www.support.xilinx.com

Spartan-6 FPGA Power Management User Guide, UG394

 Introduces the Suspend and Hibernate modes   Describes the necessary voltage supplies Introduces the low-power (-1L) devices   Describes the Power-On and Power-Down behavior Power Estimation options are discussed

Where Can I Learn More?

Xilinx Education Services courses

www.xilinx.com/training

–

Designing with Spartan-6 and Virtex-6 Device Families

course • How to get the most out of both device families • How to build the best HDL code for your FPGA design • How to optimize your design for Spartan-6 and/or Virtex-6 • How to take advantage of the newest device features

Free Video Based Training

–

How Do I Plan to Power My FPGA?

–

Power Estimation

–

What are the Spartan-6 Power Management Features?

–

What are the Virtex-6 Power Management Features?

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