Power Supply Solutions for Modern FPGAs Master Thesis Presented in Fulfillment of the Requirements for the Degree of Master of Science in the Graduate School of The Ohio State University By Amal Hassan, B.S. Graduate Program in Electrical and Computer Engineering The Ohio State University 2012 Master Thesis Committee: Professor Joanne Degroat Professor Yuan Zheng Copyright by Amal Hassan 2012 All Rights Reserved Abstract Field-programmable gate arrays (FPGAs) are used in a wide variety of applications and end markets, including digital signal processing, medical imaging, and high-performance computing. This thesis outlines the issues related to powering FPGAs. Supplying and conditioning power are the most fundamental functions of an electrical system. A loading application, be it an FPGA, cannot sustain itself without energy, and cannot fully perform its functions without a stable supply. The fact is transformers, generators, batteries, and other offline supplies incur substantial voltage and current variations across time and over a wide range of operating conditions. They are normally noisy and jittery not only because of their inherent nature but also because high power switching circuits like central processing units (CPUs) and digital signal processing (DSP) circuits usually load it. These rapidly changing loads cause transient excursions in the supposedly noise free supply, the end results of which are undesired voltage droops and frequency spurs where only a dc component should exist. The main component of a power supply is a voltage regulator. The role of the voltage regulator is to convert these unpredictable and noisy supplies to stable, constant, accurate, and load independent voltages, attenuating these ill fated fluctuations to lower and more acceptable levels. Linear or switching regulators based power supplies will be proposed and simulated. Today’s FPGAs tend to operate at lower voltages and higher currents than their predecessors. Consequently, power supply requirements may be more demanding, requiring special attention to features deemed less important in past generations. Failure to consider the output voltage, sequencing, power-on, and soft start requirements can result in unreliable power-up or potential damage to FPGAs. i Acknowledgement First and foremost, I would like to thank my advisor Professor Degroat for all her help to accomplish this goal. I am grateful for her abundant help and her prolific suggestions. Secondly, I would like to thank the personnel of the office of financial aid for providing me with the loans, the office of Electrical and Computer Engineering for a helpful orientation during both my master and bachelor, and finally the office of Graduate School of assisting me in the various class additions. Finally, I would like to thank myself for a successful education at Ohio State University while being treated with bipolar disorder. In addition, coming back to college after a long interruption and succeeding so well in spite of the illness was an achievement for me. ii Table of Contents Abstract ............................................................................................................................................. i Acknowledgement ........................................................................................................................... ii The List of Figures ............................................................................................................................ v The List of Tables ........................................................................................................................... vii Declaration .................................................................................................................................... viii I- Introduction ............................................................................................................................. 1 II- Linear versus Switching Regulators ......................................................................................... 3 III- FPGA Overview .................................................................................................................... 6 IV- Requirements of modern FPGAs.......................................................................................... 7 a. Output Voltage Requirements ............................................................................................. 7 i. Output Capacitance and Transient Considerations ......................................................... 8 ii. Transient Response Optimizations .................................................................................. 9 iii. AUX Voltage Considerations ............................................................................................ 9 b. Sequencing Requirements ................................................................................................... 9 c. Startup / Power-on Requirements ..................................................................................... 11 d. Soft-start Requirements..................................................................................................... 13 e. Synchronizing to an External Clock Requirements ............................................................ 14 f. Multiphase Operation Requirements ................................................................................ 14 g. Remote Sensing Requirements .......................................................................................... 15 V- Power Supply Examples ......................................................................................................... 16 a. Description of the first design based on a switch regulator LM20333: ............................. 16 i. Schematic overview: ...................................................................................................... 16 ii. Design description: ........................................................................................................ 17 b. Description of the second design based on a switch regulator LM22677: ........................ 28 i. Schematic overview: ...................................................................................................... 28 ii. Design description: ........................................................................................................ 28 iii c. Description of the third design based on a linear regulator LP2951: ................................ 37 i. Schematic overview: ...................................................................................................... 37 ii. Design description: ........................................................................................................ 38 d. Design of the digital control with DS1809 and Launchpad: ............................................... 42 VI- Conclusion .......................................................................................................................... 46 VII- References ......................................................................................................................... 48 Appendix A: Design Report for Design 1 ........................................................................................ 49 Appendix B: Design Report for Design 2 ........................................................................................ 52 Appendix C: Launchpad C Program ................................................................................................ 55 iv The List of Figures Figure 1: Linear Regulator Functional Diagram………………………………………………………………………….3 Figure 2: Switching Regulator Functional Diagram…………………………………………………………………….4 Figure 3: Nonisolated DC–DC Converters………………………………………………………………………………….5 Figure 4: A typical FPGA application block diagram………………………………………………………………….6 Figure 5: Simplified Buck Converter Schematic……………………………………………………………………….10 Figure 6: Startup voltage tracking……………………………………………………………………………………………..10 Figure 7: Typical voltage tracking configuration………………………………………………………………………11 Figure 8: Pre-biased startup of the LM3743………………………………………………………………………………12 Figure 9: Multiphase regulator block diagram…………………………………………………………………………..15 Figure 10: Remote-sensing block diagram…………………………………………………………………………………15 Figure 11: Power supply design 1……………………………………………………………………………………………..16 Figure 12: Duty cycle and Efficiency plots……………………………………………………………………………….18 Figure 13: Temperature and Frequency chart……………………………………………………………………………22 Figure 14: Power dissipation and Efficiency charts……………………………………………………………………23 Figure 15: Startup simulation…………………………………………………………………………………………………….24 Figure 16: Steady State chart…………………………………………………………………………………………………….25 Figure 17: Buck DC-DC converter schematic……………………………………………………………………………25 Figure 18: Gain and phase chart………………………………………………………………………………………………..26 Figure 19: Load transient response……………………………………………………………………………………………27 Figure 20: Power supply design 2……………………………………………………………………………………………..28 Figure 21: Duty Cycle and Efficiency versus IOUT……………………………………………………………………..29 Figure 22: Temperature, Efficiency and Power Dissipated………………………………………………………..30 Figure 23: Startup time……………………………………………………………………………………………………………..31 Figure 24: Switching Frequency versus RT/SYNC Resistance…………………………………………………32 Figure 25: Bode plot simulation………………………………………………………………………………………………..35 Figure 26: Steady state of the circuit…………………………………………………………………………………………36 Figure 27: Load transient