Gallium Nitride (GaN) Field-Effect Transistors (FETs) are revolutionizing power electronics due to their superior electrical properties compared to traditional silicon-based FETs. One of the most promising advancements in GaN technology is the integration of current sensing directly into the GaN FETs. This integration addresses some of the key challenges in power electronics, including efficiency, thermal management, and design simplicity.

Traditional Current Sensing 

In power electronics applications such as flyback converters, power-factor correction (PFC), and buck converters, accurate current sensing is critical for functions like peak/valley current-mode control and overcurrent protection. Traditionally, this is achieved using external components such as shunt resistors or current transformers connected in series with the main switching FET. While effective, these methods introduce several inefficiencies:

Power Losses: The inclusion of a sensing resistor in the current path results in power loss due to the voltage drop across the resistor.

Thermal Hotspots: The resistor can become a thermal hotspot, leading to heat management issues and potential reliability concerns.

Complex Design: The need for additional components complicates the circuit design, increasing the size and cost of the power electronics system.

Integration of Current Sensing in GaN FETs

Integrating the current sensing function directly into the GaN FET eliminates the need for external sensing components. This integration brings several key benefits, transforming how current sensing is implemented in power electronics: 

1. Enhanced Efficiency

• Reduced Power Losses: In traditional setups, an external sensing resistor (R_SENSE) is used to measure current, but it comes at the cost of additional power losses and unwanted heat generation. The integrated current sensing solution eliminates the need for this external resistor, which not only minimizes power losses but also avoids creating hot spots in the system. This efficiency gain is particularly valuable in high-performance applications.
• Cost Savings with Higher RDS (on): By integrating current sensing into the GaN FET, designers can opt for a FET with a slightly higher drain to source resistance (R_{DS on}) without compromising overall efficiency. The reason is that the losses avoided by removing external sensing resistor (R_SENSE) balance out the slightly higher conduction losses. This flexibility can result in cost savings since FETs with higher (R_{DS on}) are typically less expensive.

2. Improved Drive Circuit Performance

• Cleaner Signal Paths: The integrated solution allows for the use of a Kelvin source connection, which separates the gate drive circuit from the main power circuit. This separation results in a more stable signal, reducing noise and improving the overall performance of the drive circuit.
• Avoiding Common Inductance Issues: In a discrete GaN setup, the presence of common source inductance and the voltage fluctuations caused by external sensing resistor (R_SENSE) can negatively affect the drive circuit’s performance. Integrated current sensing circumvents these issues by performing the sensing internally, thus ensuring more stable operation.

3. Simplified Design and Integration

• No Need for Additional Power Supplies: The integrated current sensing function does not require an additional external power supply. This makes the design more compact, reduces the number of components, and simplifies the overall system, making it easier to use and more space-efficient.

4. Easy Transition from Conventional Systems

• Smooth PCB Design Migration: By replacing the sensing resistors with 0-Ω resistors, the existing PCB layout can be easily adapted to accommodate the new integrated component. This allows for a seamless upgrade without the need for a complete redesign.

5. Simplified Parallel Operation

• Facilitated Paralleling: In power electronics, it’s often necessary to parallel multiple FETs to handle higher currents. The integrated current sensing solution makes this easier by inherently balancing the current between parallel devices, which reduces the need for additional external circuitry and ensures smoother operation.

6. Increased ESD Protection

• Robust ESD Rating: GaN FETs are generally more vulnerable to electrostatic discharge (ESD) compared to their silicon counterparts. However, the integrated solution includes an auxiliary circuit that significantly boosts the ESD protection from 200 V to 2 kV. This makes the GaN FETs much more robust and reliable, reducing the risk of damage from ESD events.

Practical Validation and Results

The integration of current sensing in GaN FETs has been validated through extensive testing. This test included a 400-V, 6-A double-pulse test, which demonstrated clean switching and accurate, fast current sensing with a 200-nanosecond response time. In addition, a 60-W GaN adapter test showed a 0.4% efficiency gain over traditional setups, highlighting the practical benefits in both efficiency and thermal performance.