Emerging Trends in Wide Bandgap Gate Drivers

Silicon Carbide (SiC) and Gallium Nitride (GaN) technologies are both constantly improving with higher voltage ratings and lower switching losses. SiC MOSFETs rated at up to 2200V are now available as individual devices or packaged in modules containing up to six devices. GaN devices are still mostly 650V, but modules with a 1200V rating are expected mid-2024.

Gate driver ICs serve as the interface between control signals from digital or analog controllers and the power switches (IGBTs, MOSFETs, SiC MOSFETs, or GaN HEMTs). They provide the high drive currents needed to overcome the gate capacitance for fast switching and isolate the low voltage drive signals from the high-side voltage referenced transistor terminals. Increasingly, isolated gate drivers are also being used for low-side transistors to eliminate the effect of inductive path imbalances. Gate drivers thus play a crucial role in optimizing WBG transistor performance and reliability, and they are constantly evolving to meet new challenges.

Integrated gate driver solutions, for example, often combine multiple drivers with protection features and fault detection. These products reduce design complexity, development time, bill of materials (BOM) cost, and improved reliability versus discretely implemented designs.

For example, half-bridge GaN drivers are available that include independent and TTL-compatible top and bottom driver stages, logic control, and protections against short circuit, undervoltage, and overvoltage conditions. These devices can be configured into various topologies, including synchronous half-bridge, full-bridge, buck, boost, and buck-boost configurations.

Ultra-fast gate drivers are another recent development. Recently-introduced devices can deliver up to 7A output current with rise and fall times of 0.65ns and 0.70ns respectively into a 200 pF load. With a gate driver voltage range of 4.5V – 5.5V, these drivers are tailored for GaN devices.

What all of these isolated gate drivers have in common is the need for an isolated power supply for the isolated output stage. Despite the high peak currents, the average power consumption is only a few watts, so these DC/DC power supplies can be made very small. A further requirement is the need to generate asymmetric voltages. For example, many SiC transistors reach peak performance when driven by a +18V to -4V gate drive voltage. Other devices may need different optimal gate drive voltages, for example, +20V/-5V, +15V/-3V, +6V/-1V, or +15V/-9V.

Given the difficulties inherent in driving WBG transistors, it’s not surprising that some manufacturers are trying to avoid the problems altogether by combining SiC or GaN power devices and gate drivers into a single package. There are advantages and disadvantages to this approach. The advantages include:

• Space efficiency. Combining gate drivers and power transistors in a single package reduces the printed circuit board (PCB) footprint, simplifying the layout and lowering cost.
• Reduction in parasitics. Integrating gate drivers and power transistors minimizes the interconnection length between them. This reduction in parasitic inductance and capacitance improves switching performance and reduces electromagnetic interference (EMI).
• Enhanced performance. Co-packaging allows for optimized gate drive circuitry. The gate driver can be tailored specifically for the characteristics of the power transistor, ensuring efficient switching and reduced switching losses.
• Improved thermal performance. Heat dissipation is more effective when gate drivers and power transistors share the same thermal path, resulting in better thermal management and increased reliability.

Of course, there are potential disadvantages, too.

• Limited Flexibility. Integrated packages may not offer the flexibility to choose different gate drivers or power transistors independently.
• Isolation Requirements. Gate drivers and power transistors need electrical isolation to prevent cross-talk and ensure safety. Co-packaged solutions must address isolation requirements effectively.
• Testing and Debugging Complexity. Troubleshooting becomes more challenging when gate drivers and power transistors are combined. Isolating faults or failures requires specialized tools and expertise.

Although co-packaging advantages may overcome the disadvantages for high-speed switching with steep turn-on and turn-off slopes, there is still a need for external isolated power supplies. These DC/DC converters need to be able to cope with the high dv/dt switching transitions, so must have a low isolation capacitance and a high CMTI immunity.

RECOM has several families of isolated DC/DC converters suitable for supplying SiC and GaN gate drivers.

SiC MOSFETs. The RxxP22005D and RKZ-xx2005D series feature asymmetric outputs of +20V and -5V to switch the SiC MOSFET efficiently and effectively. The RxxP21503D series provides asymmetric output voltages of +15 and -3V, which are needed to switch second-generation SiC MOSFETs efficiently.

GaN HEMTs. High slew-rate GaN transistor drivers reach optimal performance switching at +6V from RECOM’s DC/DC converters RP-xx06S and RxxP06S series featuring high isolation voltage and low isolation capacitance. In GaN applications where higher noise and interference must be considered, RECOM also offers converters with +9V output which can be split up via a Zener diode to +6V and -3V to provide a negative gate voltage on turn-off ensuring that the gate voltage stays below the turn-on threshold.

The table below summarizes the recommended DC/DC converters for WBG devices and IGBTs.

IGBT RxxP2xx, RxxPxx, RP, RH & RKZ series in a compact SIP7 case RV & RGZ series in a low profile DIP14 and mini DIP24 case +15V and -9V outputs Up to 6.4kVDC isolation 5V, 12V or 24V inputs 1W or 2W total outputs Symmetric power Up to 86% efficiency Up to +90°C operating temperature EN certified 3 year warranty

SiC RxxP21503D, RxxP22005D, RKZ-xx2005D series in a compact SIP7 case +15/-3V & +20/-5V outputs SMD RA3 series with +15/-5, +15/-3 or +20/-5V outputs Up to 6.4kVDC isolation 5V, 12V, 15V or 24V inputs 2W total output (3W for RA3) Symmetric power or symmetric current output Up to 87% efficiency Up to +90°C operating temperature EN/IEC/UL certified 3 year warranty

GaN RJZ, RK, RP, RV, RxxPxx, RxxP2xx in a compact DIP14, DIP24 or SIP7 cases +6V & +9V outputs SMD RA3 series with +7/-1, +8V or +9V outputs Up to 6.4kVDC isolation 5V, 12V, 15V, or 24V inputs 1W or 2W output power (3W for RA3) Up to 83% efficiency Up to +90°C operating temperature EN/IEC/UL certified 3 year warranty

The R-REF-HB Half-Bridge Gate-Drive Power Supply Reference Design (RD) consists of a half-bridge suitable for voltages up to 1kVDC and a fully isolated driver stage with isolated power supplies for both low-side and high-side switching transistors.

The R-REF01-HB includes two R12P22005D, R12P21503D, R12P21509D, and R12P06S DC/DC converters and can generate gate drive voltages suitable for SiC and GaN devices. With these converters the following gate drive voltages can be generated:

• +20V/-5V
• +15V/-3V or +18V*
• +15V/-9V
• +6V

RECOM engineers closely follow developments in this area and recommend the appropriate gate driver power supplies as new devices come on the market.

For example, Gen IV 35mΩ 650V GaN FETs are available in a TO-247 package with an additional Kelvin source pin for optimal switching control. RECOM recommends using the R-REF01-HB with a +15/-3V date driver voltage to get the maximum performance from this new technology.

WBG power device technology is a fast-moving field and new gate drivers are always hitting the market to accommodate new devices and topologies. RECOM follows this market closely and our engineers will be able to recommend the appropriate power supply solution for your WBG application.