GaN is finally cheap enough to reach for on everyday projects, not just aerospace and RF power budgets. Here’s an interesting post by EPC (one of the largest GaN vendors) on why it works the way it does.
The short version: GaN switches faster and handles more power in the same area than silicon. Higher breakdown voltage in a smaller package, lower on-resistance, faster switching, better thermal conductivity. On a 4kW motor controller we built (see the bottom of this post), that combination got us 98% efficiency at 3kW in a package 40% smaller and 50% lighter than the silicon predecessor it replaced.
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), typically under 2V, which makes turning them on significantly easier than their silicon-based counterparts which typically require 5 volts or more.
This image shows the threshold voltage characteristics of a very high power GaN FET, the EPC2302.
Important: Don’t drive a GaN device directly with GPIO. GPIO output impedance is too high for it, and doing so gives poor switching performance and risks MCU damage 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
Higher is better. Look for 4A or more source/sink for fast switching; higher drive current cuts switching losses. Size the driver against the gate charge (Qg) of the specific device you’re using.
2. Propagation delay
Lower is better. Target under 50ns for high-frequency applications, with matched delays between high-side and low-side drivers to prevent shoot-through. Check delay drift over temperature, not just the room-temperature number.
3. Isolation
Not always necessary, but it raises the safety margin. Galvanic isolation protects control circuits from power-stage faults; digital isolators give fast switching with good noise immunity. Floating high-side drivers often need an isolated supply anyway.
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, with wide traces and short connections. A four-layer board with dedicated power and ground planes makes this much easier than trying to route it on two layers.
2. Thermal management
Thermal vias under the GaN device, copper pour for heat spreading, and enough airflow or heatsinking for the actual power level, not just the datasheet’s best case.
3. EMI
GaN’s fast switching pushes more energy into higher frequencies than silicon does. Filter every input and output connection, and shield sensitive circuits that sit near the switching node.
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
Weak gate drivers or long gate traces slow the switching edge and cancel most of the efficiency gain. Use a dedicated driver sized for the actual gate charge. Underestimated thermal design catches people who are used to silicon’s larger, more forgiving packages. Model the thermal path before layout, not after. High-inductance layouts cause voltage spikes that overvoltage-stress the device, follow the manufacturer’s GaN-specific layout guidelines rather than reusing a silicon MOSFET layout. And GaN devices are not indestructible: skipping protection because “GaN is robust” is how a fault event takes out the whole power stage.
Cost
GaN costs more per device than an equivalent silicon MOSFET. It makes economic sense in high-volume designs where the efficiency gain lowers system cost elsewhere (smaller magnetics, smaller heatsink), in size-constrained designs where the volume reduction itself has value, and in high-frequency designs where silicon simply can’t hit the target switching frequency. A reference design from EPC, GaN Systems, Navitas, or Infineon cuts development time; factor in the full system cost, including magnetics and cooling, not just the device price, when comparing to silicon.
The Bottom Line: Get the Gate Drive and Thermal Path Right First
GaN requires more careful design than dropping in a silicon MOSFET, but the performance gains are real. Get the gate drive right, plan the thermal management, and follow the manufacturer’s layout guidelines rather than adapting a silicon design.
- EPC GaN Design Resources
- GaN Systems Application Notes
- Infineon CoolGaN Documentation
- IEEE Power Electronics Society, technical papers and conferences
We used this exact approach on a 4kW GaN motor controller, 40% smaller and 50% lighter than the silicon-based predecessor.