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Tips for Working with GaNFETs

Learn the basics of designing electronics with GaN FETs for better efficiency, smaller size, and superior performance.

Orion Serup
#gan #power electronics #semiconductors #design
Tips for Working with GaNFETs

Gallium Nitride (GaN) based semiconductor devices are the future of power and high frequency electronics and are only just now starting to become economically viable for everyday projects. Here is an interesting post by EPC (one of the largest designers of GaN technology) which breaks down the main benefits and applications of GaN.

GaN devices are better in almost every way compared to current silicon-based technology. They are able to handle more power in the same area as well as turn on and off faster than comparable silicon-based devices. This combination of speed and power density leads to vast increases in efficiency as well as significant decreases in the size of circuitry.

Why GaN Matters for Modern Electronics

Superior Material Properties

GaN’s fundamental material properties make it ideal for power applications:

  • Higher breakdown voltage - Can handle much higher voltages in smaller packages
  • Lower on-resistance - Reduces conduction losses and heat generation
  • Faster switching - Enables higher frequency operation with lower switching losses
  • Better thermal conductivity - Handles heat dissipation more effectively than silicon

Real-World Performance Benefits

In practical applications, GaN devices typically deliver:

  • 30-50% efficiency improvements over silicon MOSFETs
  • 3-5x smaller form factor for equivalent power handling
  • 10x faster switching speeds enabling MHz switching frequencies
  • Reduced cooling requirements due to lower losses

Driving GaN Devices

The goal when driving a GaN device is to switch it on and off as fast as possible. The faster you can switch the device on and off, the more efficiently it will operate.

GaN devices generally have a low Gate Threshold Voltage (Turn On Voltage) of less than 2V or so, which makes turning them on significantly easier than their silicon-based counterparts which typically require 5 volts or more.

GaN Threshold Voltage

This image shows the threshold voltage characteristics of a very high power GaN FET, the EPC2302.

Important Note: It is not advisable to drive a GaN device with GPIO directly in most cases due to the relatively high output impedance delivered by the GPIO pins. Doing so will result in poor switching performance and possible damage to the MCU in a fault scenario.

GaN Gate Drivers

The best way to drive the gate of a GaN device is to use a specialized driver IC. EPC has a comprehensive list of gate drivers for every application here.

When choosing a gate driver, there are several factors to keep in mind:

1. Current Source and Sink Ability

The higher the better generally

  • Look for drivers that can source/sink 4A or more for fast switching
  • Higher drive current reduces switching losses and improves efficiency
  • Consider the gate charge (Qg) of your GaN device when sizing the driver

2. Propagation Delay

The lower the better generally

  • Target delays under 50ns for high-frequency applications
  • Matched delays between high-side and low-side drivers prevent shoot-through
  • Consider temperature variations in delay specifications

3. Isolation

Not strictly necessary but significantly increases system safety

  • Galvanic isolation protects control circuits from power stage faults
  • Digital isolators offer fast switching with good noise immunity
  • Isolated supplies may be required for floating high-side drivers

Advanced Driver Considerations

Bootstrap vs. Isolated Supply

For high-side gate drive:

  • Bootstrap circuits are simple and cost-effective for most applications
  • Isolated supplies provide better performance for continuous operation
  • Consider duty cycle limitations with bootstrap approaches

Dead Time Management

  • GaN devices switch so fast that traditional dead time becomes critical
  • Adaptive dead time controllers can optimize efficiency
  • Consider using integrated half-bridge drivers with built-in logic

Protecting GaN Devices

GaN devices, while robust, require careful protection due to their fast switching and high power density.

Overvoltage Protection

  • TVS diodes on drain connections for voltage spikes
  • Gate clamping to prevent gate oxide damage
  • Snubber networks to control dv/dt during switching

Overcurrent Protection

  • Current sensing with fast response times
  • Desaturation detection for short-circuit protection
  • Thermal monitoring to prevent overheating

Layout Considerations for Protection

  • Low inductance layouts to minimize voltage spikes
  • Proper grounding to avoid ground bounce issues
  • Adequate thermal management for sustained operation

PCB Design Guidelines for GaN

Critical Layout Rules

1. Minimize Loop Inductance

  • Keep gate drive loops as small as possible
  • Use wide traces and short connections
  • Consider four-layer boards with dedicated power/ground planes

2. Thermal Management

  • Use thermal vias under GaN devices
  • Consider copper pour for heat spreading
  • Plan for adequate airflow or heatsinking

3. EMI Considerations

  • GaN’s fast switching can create EMI challenges
  • Use proper filtering on input/output connections
  • Consider shielding for sensitive circuits

Component Selection

Gate Drive Components

  • Low-ESR ceramic capacitors for gate drive supply bypassing
  • Fast recovery diodes if using bootstrap supplies
  • Quality resistors for gate drive current limiting

Power Stage Components

  • Low-ESL capacitors for DC bus filtering
  • High-frequency capable inductors for switching applications
  • Fast diodes for freewheeling (though GaN often eliminates this need)

Application Examples

DC-DC Converters

GaN excels in:

  • Buck converters for voltage regulation
  • Boost converters for power factor correction
  • LLC resonant converters for isolated supplies

Design Tips:

  • Switch at 500kHz-2MHz for optimal efficiency
  • Use synchronous rectification to eliminate diode losses
  • Consider continuous conduction mode for best efficiency

Motor Drives

GaN enables:

  • Higher switching frequencies for better motor control
  • Smaller filter components due to higher frequency
  • Improved efficiency especially at light loads

Design Tips:

  • Dead time optimization is critical for efficiency
  • Consider sine wave reconstruction quality
  • Plan for adequate gate drive isolation

Wireless Power Transfer

GaN’s high frequency capability enables:

  • Smaller coil designs at higher frequencies
  • Better efficiency over distance variations
  • Faster charging with higher power density

Common Design Pitfalls

1. Inadequate Gate Drive

Problem: Using weak gate drivers or long gate traces Solution: Use dedicated gate drivers with sufficient current capability

2. Poor Thermal Design

Problem: Underestimating thermal requirements Solution: Proper thermal modeling and heat dissipation planning

3. Layout Issues

Problem: High inductance layouts causing voltage spikes Solution: Follow GaN-specific layout guidelines from manufacturers

4. Insufficient Protection

Problem: Assuming GaN devices are indestructible Solution: Implement comprehensive protection schemes

Cost Considerations

When GaN Makes Economic Sense

  • High-volume applications where efficiency savings justify cost
  • Size-constrained designs where volume reduction has value
  • High-frequency applications where silicon performance is inadequate

Cost Reduction Strategies

  • Use proven reference designs to reduce development time
  • Partner with suppliers for application support
  • Consider total system cost including magnetics and cooling

Technology Improvements

  • Lower cost manufacturing making GaN more accessible
  • Integrated solutions combining GaN with drivers and protection
  • Higher voltage ratings expanding application range

Market Adoption

  • Automotive applications driving volume and cost reduction
  • Data center efficiency requirements accelerating adoption
  • Consumer electronics adopting GaN for fast charging

Getting Started with GaN

  1. Start with evaluation boards from established suppliers
  2. Use reference designs as starting points
  3. Focus on thermal and layout considerations early
  4. Plan for comprehensive testing including EMI and thermal

Supplier Resources

  • EPC - Comprehensive application notes and design tools
  • GaN Systems - Automotive and industrial focus
  • Navitas - Integrated GaN solutions
  • Infineon - CoolGaN family for various applications

Conclusion

GaN technology represents a fundamental shift in power electronics design. While the devices themselves are more capable than silicon, they require careful consideration of gate drive, protection, and thermal management.

The key to successful GaN implementation is understanding that you’re not just replacing a silicon MOSFET - you’re designing with a fundamentally different technology that enables new levels of performance.

For engineers willing to invest the time to understand GaN’s unique characteristics, the rewards include significantly improved efficiency, reduced size, and enhanced performance that simply isn’t possible with traditional silicon devices.

The future of power electronics is clearly moving toward wide bandgap semiconductors like GaN. Early adoption and experience with these technologies will become increasingly valuable as the market continues to evolve.

Additional Resources