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Pre-Conference Seminar: Putting GaN to Work in your Power Supply

Presented by: Robert V. White, Chief Engineer, Embedded Power Labs

Robert White

Date: Tuesday, September 18, 2012
Time: 1:30 - 5:00 p.m.
Location: DoubleTree by Hilton, San Jose, CA
Fee: $50 with DPF registration; $450 for seminar only

Abstract

Gallium nitride (GaN) based power switching devices are now available from multiple suppliers. These devices offer much faster and lower loss switching than today's silicon MOSFETs – and promise smaller and more efficient power supplies and dc-dc converters.

Just as power supply engineers 30 years ago had to learn new techniques to use the newly introduced MOSFETs, today's engineers will have to learn some new techniques to put GaN devices to work in their designs.

This seminar starts with a comparison of the material properties of silicon, silicon carbide, and gallium nitride. How the material properties relate to the electrical device properties is explained. Next is a description of the structure and basic operating principal of GaN switching devices. Then key specifications of GaN switches and silicon MOSFETs with similar voltage and current specifications are compared.

With an understanding of the GaN switches, the discussion moves on to explore the circuit techniques needed to drive the gates of both depletion mode and enhancement mode GaN devices are shown. The implications of switching with nanosecond rise and fall times are discussed, with special attention given to the importance of minimizing the common source inductance is discussed. Some problems with making accurate measurements are briefly discussed.

The seminar then shows examples of a 48 V to 1.2 V buck converter and a dual active bridge isolated dc-dc converter using GaN devices, including experimental data. The advantages and disadvantages of GaN devices in each are discussed.

The last section of the seminar addresses the application issues of paralleling GaN devices, PCB layout, and thermal management.

Please click here to register for both DPF and this seminar (please click the check box listed under "Available Options" before clicking the "Add to Cart" button), or click here to register for the seminar only. For questions or more information please contact Traci Shepard.

Full Disclosure Note

This seminar was developed in conjunction with Efficient Power Conversion (EPC). Most of the material presented in this seminar will be provided by EPC.

The goal of the seminar, however, is to promote the use of GaN in general and not just those devices offered by EPC. The basic structure of the GaN on silicon HEMT devices and the 2-D electron gas they use is not supplier specific. That the gates are not silicon oxide capacitors, and what that means for driving the gates, is not manufacturer specific. The implications of nanosecond switching are not supplier specific. In the circuit and application examples as much detail is given to driving depletion mode devices as enhancement mode devices.

However, the dc-dc converter circuit examples will be based on applications work done by EPC and will show EPC’s enhancement mode devices

Note that only EPC parts will be used for discussion as there are no other commercially available parts with publically available data.

The slides will use a generic background (neither EPC's format and logo nor Embedded Power Labs format and logo). I will be identified on the title slide as a consultant to EPC and I am planned as the only speaker. The slides will be identified as "©Efficient Power Conversion".

Target Audience

This seminar is suitable for anyone interested in the use and application of GaN devices, both engineer and non-engineer, at all levels of expertise.

Outline

Introduction
  • Seminar purpose, description, timing, mechanics
  • Overview of seminar
What Is A GaN Device?
  • GaN on silicon structure
    • Planar, not vertical device
    • HEMT, not a MOSFET
      • 2-D electron gas
    • Gate is not a MOS capacitor
    • Body diode: higher VF than silicon MOSFET but no QRR
  • Device operation
    • Depletion mode
    • Enhancement mode
  • Flip chip structure advantages
    • Small size
    • Very low parasitic inductance
    • No lead frame resistance
  • Compare and contrast to a silicon MOSFET
    • On resistance
    • Device capacitances
    • Switching speed
    • Body diode characteristics
Driving GaN Devices
  • Gate characteristics
    • Voltage limitations
    • Capacitance
    • Resistance
    • Leakage currents
  • Driving depletion mode devices
    • With negative voltage driver
    • Cascade drivers
  • Driving enhancement mode devices
    • With discrete circuitry
    • With National Semiconductor's integrated driver
  • Implications of nanosecond switching
    • Importance of common source inductance
    • Measurement considerations
Circuit Example: 48 V to 1.2 V Buck Converter
  • GaN speed allows very small duty cycles
  • Circuit schematic and components
  • Experimental data
  • Compared and contrasted to silicon MOSFET based converter
  • Summary points: GaN allows
    • Higher speed and smaller size than silicon at same efficiency
    • Higher efficiency than silicon at same speed
Circuit Example: Dual Active Bridge Isolated DC-DC Converter
  • Circuit schematic and components
  • Experimental data
  • Compared and contrasted to silicon MOSFET based converter
  • Summary points
Application Information
  • Paralleling GaN devices
    • What mismatches are important?
    • Driver design for paralleling
  • PCB layout
    • Flip chip considerations
    • Parasitic inductances and capacitances
  • Thermal considerations for flip-chip devices
    • Cooling paths
      • Through mounting solder balls into PCB
      • Through the back side
    • Typical device thermal characteristics
Questions and Answers

Speaker Biography
Bob White, Chief Engineer, Embedded Power Labs

Bob has broad experience in designing power supplies, dc-dc converters and power systems for electronic equipment. He is widely recognized as an expert in power systems architecture and digital power management. Bob is the principal author of the PMBus™ specifications. He is a well known speaker and author who has presented many papers and seminars at conferences such as the IEEE Applied Power Electronics Conference (IEEE APEC), the European Power Electronics Conference (EPE), the IEEE International Telecommunications Energy Conference (INTELEC) and the IEEE International Congress on Power Electronics (CIEP). In more than 30 years of professional experience, Bob has worked for Emerson Network Power/Artesyn Technologies/Zytec Corporation, AT&T Bell Labs/Power Systems, the Digital Equipment Corporation and General Electric.

Bob has a BSEE from MIT (1980) and a MSEE from the Worcester Polytechnic Institute (1991).

He is a Fellow of the IEEE, in which he has been active for more than 20 years. He was elected to the Power Electronics Society’s executive committee three times, served two terms as the Society’s Technical Vice President. Bob is well known for his key role in developing and supporting the IEEE Applied Power Electronics Conference (APEC). Bob was awarded the IEEE Third Millennium Medal in 2000 and the IEEE Power Electronic Society’s Distinguished Service Award in 2002. The Power Sources Manufacturers Association (PSMA) recognized Bob in 2005 for his contributions to and leadership of the PSMA and APEC.

Recent Publications

"Introduction To Microcontrollers", APEC 2011 Professional Education Seminar
"Writing Specifications For Power Supplies And DC-DC Converters", APEC 2011 Professional Education Seminar
"High Step-Down Ratio Buck Converters With eGaN Devices", How2PowerToday Newsletter, November 2010 (Co-Author)
"Practical Issues In Monitoring And Reporting Input And Output Power", COMPEL 2010
"Digital Power – After the Hype", APEC 2010, Invited Plenary Session Presentation
"Understanding And Using The PMBusTM Protocol", APEC 2008 Professional Education Seminar
"Data Communications Issues For Digital Power Management", APEC 2007 (Co-Author)
"Configuring Systems For Operation From Three Phase Power", APEC 2007 (Co-Author)
"Designing Power Systems For Electronic Equipment", APEC 2007 Professional Education Seminar
"Sampling And Averaging Considerations For Measuring Input Power", IBM 2007 Power And Cooling Symposium
"Digital Control Concepts For Power Supply Engineers", Darnell Digital Power Forum 2006
"PMBusTM – Enabling Intelligent Power System Management", Darnell Digital Power Forum 2006
"Understanding And Using PMBusTM Data Formats", APEC 2006 (Co-Author)
"Electrical Isolation Requirements In Power-Over-Ethernet (PoE) Power Sourcing Equipment (PSE)", APEC 2006
"Using Redundant DC Power In High Availability Systems", APEC 2006
"Digital Power System Management", APEC 2006 Professional Education Seminar
"Using The PMBusTM Protocol To Manage Your Power System", Darnell Digital Power Forum 2005
"Digital Power System Management", APEC 2005
"Digital Power System Management", , APEC 2005 Professional Education Seminar

Please click here to register for both DPF and this seminar (please click the check box listed under "Available Options" before clicking the "Add to Cart" button), or click here to register for the seminar only. For questions or more information please contact Traci Shepard.

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