Isolated GaN Driver Boosts Device Performance and Supports Safe Operation

While silicon-carbide (SiC) power devices have been getting considerable and much-deserved attention lately, it has a “competitor”: devices based on gallium nitride (GaN, and to be more precise, it’s actually GaN on Si), another wide-bandgap process technology.

Just as with any power device, these GaN switches need drivers that translate low-level controls signals into the higher voltages and currents they need to be effectively switched between on and off states—and with controlled timing. Further, many system applications also need galvanic (ohmic) isolation, which can be provided by a separate component or integrated into the driver.

To meet these requirements, STMicroelectronics introduced the STGAP2GS, its first galvanically isolated gate driver (1,200-V isolation) for GaN transistors. The single-channel driver can be connected to a high-voltage rail up to 1,200 V (or 1,700 V with the narrow-body STGAP2GSN version) and provides gate-driving voltage up to 15 V.

The drivers are suitable for mid- and high-power applications such as motor drivers for home appliances, factory automation, industrial drives and fans, UPSs, wireless chargers, and power-conversion and motor-driver inverters in industrial applications (Fig. 1).

1. This application diagram shows a typical positive gate-driving arrangement using the STGAP2GS GaN driver. The datasheet also shows a negative gate-driving arrangement.

The STGAP2GS is intended to drive enhancement-mode GaN FETs, thanks to its separate turn-on and turn-off output pins and to the optimized undervoltage-lockout (UVLO) protection. The gate driver offers 2-A current-source and 3-A current-sink capability plus rail-to-rail outputs. In addition, it’s driven by 3.3/5-V TTL/CMOS inputs with hysteresis. The STGAP2GS has separate sink and source pins for easy tuning of the gate-driving operation, and independent control with optimized turn-on and turn-off times via dedicated gate resistors.

Propagation delay across the 1,200-V isolation barrier is just 45 n, ensuring fast dynamic response. Furthermore, dV/dt transient immunity of ±100 V/ns over the full temperature range guards against unwanted transistor gate change.

The dual input pins allow for the selection of signal polarity control and implementation of HW interlocking protection to avoid cross-conduction in the event of controller malfunction. A standby mode is available to reduce idle power consumption.

Even basic devices such as a gate driver need design-in and applications support. In addition to the 20-page datasheet, ST offers two similar demonstration boards (Fig. 2): the EVSTGAP2GS for the STGAP2GS (SO-8 widebody package) and similar EVSTGAP2GSN for the STGAP2GSN (SO-8 narrow body package).

2. Two similar demo boards are available for the drivers: the EVSTGAP2GS for SO-8 widebody devices (left) and similar EVSTGAP2GSN for the SO-8 narrow body package (right).

These boards combine either driver with ST’s SGT120R65AL 75-mΩ, 650-V enhancement-mode GaN transistors to help users evaluate the drivers’ capabilities. The board components are easy to access and modify to make their performance evaluation easier under different application conditions as well as enable fine adjustment of final application components.

Both the SO-8 wide-body STGAP2GS and the SO-8 narrow version STGAP2GSN are available now, priced from $1.42 for orders of 1,000 pieces.