Power Electronics Europe Issue 4 - November 2022

https://www.allegromicro.com/en/ GATE DRIVERS 9 www.power-mag.com Issue 4 2022 Power Electronics Europe the need for circuits such as snubbers or filters required to manage these phenomena. Allegro has developed the AHV85110 and AHV85111 isolated GaN and MOSFET drivers with Power-Thru magnetic isolation to make this process easier, resulting in more effective gate drive designs. Evaluation The Allegro APEK85110 Half-Bridge Driver Switch Board is a demo board containing two AHV85110 gate drivers and two GaN FETs in a half-bridge configuration. This can be used to perform double pulse tests or to interface the half bridge to an existing LC power section. The isolated AHV85110 driver does not require secondary-side power or bootstrap components. Gate drive power is supplied to the secondary side from the primary- side supply voltage, V DRV , and the amplitude of the gate drive can be varied by varying V DRV between 7 and 15 V. The evaluation board uses a bipolar gate drive arrangement, which is useful to mitigate against the effects of gate-drain capacitor currents. The secondary supply voltage is a function of the primary supply voltage and the Zener diode regulates the positive power-on voltage of the GaN FET. During the power-off period, the gate voltage is negative to allow more margin before the threshold voltage can be reached. Ensuring availability To keep production lines running, availability of devices is also key amidst a shortage of components for automotive designs. Car makers around the world have suffered from shortages of components such as gate drivers, and designers are increasingly aware of the supply chain issues of the devices they use. The innovative magnetic isolation of the Allegro Power-Thru devices is built on standard 180 nm CMOS technology from dual-sourced tier one fabs, allowing flexibility of sourcing. Industry-leading packaging vendors and a range of second- source strategies are also used to ensure a secure supply of devices for some of the smallest high-voltage and high-efficiency power systems available. Conclusion The choice of gate driver is a key decision in the development of the power system of an electric vehicle. Whether this is a car, scooter, mining dump truck or tractor, the gate driver is there, controlling the power transistors in any power-conversion system. The move to SiC and GaN transistors means there are many more factors for a designer to consider. The higher power, higher temperatures, and higher frequencies used with these devices are putting more focus on reliability of the design, which in turn is driving a reduction in the number of components. Smaller weight and size are also driving down the size of designs. All of this is driving up the levels of integration and the demands on the gate driver devices. The Power-Thru magnetic isolation in the Allegro gate drivers enables higher levels of integration that can help to address issues such as EMI and parasitic effects on the board, reducing the time needed to design, test, and certify a system. All these factors—along with the secure supply of the components in the design— must be considered when designing a power system for an electric vehicle. Figure 4: How the gate driver pinout reduces current loops in the PCB. Figure 5: The APEK85110 half-bridge driver switch board.board.