100-V Silicon MOSFETs Keep Pace with SiC and GaN Counterparts

What you’ll learn: 

• Silicon MOSFETs are still viable and receiving ongoing process and R&D efforts.
• How and why the latest mid-voltage silicon MOSFET from Renesas proves it.
• The features of a development kit that eases integration in BLDC motors.

Despite all of the deserved attention on silicon-carbide (SiC) and gallium-nitride (GaN) power-switching devices, silicon MOSFETs are still seeing significant R&D and process developments, specifically when you get down to voltages of 100 V or less.

In one of the latest technological advances, Renesas Electronics introduced a pair of 100-V N-channel MOSFETs that deliver industry-leading high-current switching performance: the RBA300N10EANS and RBA300N10EHPF. The 340-A MOSFETs target applications such as motor control, battery-management systems, and charging subsystems in smaller electric vehicles, e-bikes, charging stations, power tools, data centers, and uninterruptible power supplies (UPS).

The AEC-Q101-qualified MOSFETs are based on a new wafer-manufacturing process that Renesas calls REXFET-1. The split-gate technology inside them drastically improves key performance metrics. Outstanding among these enhancements is a 30% reduction in the drain-source on-resistance (R_DS(ON)) to a maximum of 1.5 mΩ, which results in much lower power loss. There is also a 10% reduction in Q_g—the amount of charge needed to apply voltage to the gate in the MOSFET—and a 40% drop in Q_gd—the amount of charge that needs to funnel into the gate during the "Miller Plateau" phase.

In case you’ve forgotten about the Miller effect and its “spinoff,” the Miller plateau, here’s a reminder: After the gate voltage rises past the threshold and drain current reaches its limit (set by the current-limiting circuit), the V_ds starts to fall, displacing charge on C_gd through the gate. While V_ds falls to zero volts from V_dd, V_G is stuck by the displacement current from C_gd. That current is the Miller Plateau.

The main differences between the MOSFETs pertain to packaging. They come in industry-standard TOLL and TOLG packages (Fig. 1), measuring approximately 10 × 10 mm. Pin-compatible with power MOSFETs from other manufacturers, the packages are 50% smaller compared to traditional TO-263 varieties. In addition, the TOLL package also offers wettable flanks for optical inspection.

The datasheets contain the requisite tables with ratings, along with performance charts and graphs for factors such as safe operating area (SOA) and transient thermal impedance versus pulse width (Fig. 2).

To support design-in with these MOSFETs, Renesas rolled out the TOLL 48V Power Line Evaluation Board. The inverter uses the TOLL-package MOSFET along with the RL78/F14 microcontroller (MCU) to drive a three-phase brushless DC (BLDC) motor. It provides a versatile platform for testing and evaluating motor-control systems, with precise speed control and efficiency that stems from its two main components: the Power Board and the Controller Board.

The Power Board (TMS-2000W-ISG-INV-R2.0) is responsible for providing the necessary power to drive the motor (Fig. 3), while the Controller Board (TMS-RL78F14-ISG-CTR-R1.0) handles the control and feedback signals (Fig. 4).

Together, these boards create a full solution for driving three-phase BLDC motors with precision and accuracy (Fig. 5). The power stage of the TOLL 48V EVB operates at 12- to 48-V DC voltage, while a separate 12-V DC supply powers the driver circuit. What’s more, the controller derives its 5-V rail from the 12-V rail. The board can deliver a maximum of 700 W at 48 V with a maximum output current of 70 A.

For those interested in the underlying process and packaging technologies behind the MOSFET, Renesas also fills in the details in its application note, aptly titled, “MOSFET REXFET-1: Middle-voltage product-technology development.”