51 Power semiconductors | Deep insight E-Mobility Engineering | March/April 2024 MOSFETs in all high-current applications and boosts the power density of a design. Compared with the previous seven-pin Double Decawatt Package (D2PAK), the TOLL devices have a 30% smaller footprint on a board and half the height, saving space. The lower package parasitic inductances also result in improved EMI behaviour. The 50% bigger solder contact area on the TOLL package also avoids electro-migration at high current levels, improving reliability. Power semiconductor tech The basic technologies for power are the bipolar junction transistor (BJT), MOSFET and IGBT. All have three main connections to the outside: a collector, emitter and base in the BJT; a gate, source and drain in the MOSFET; and a collector, gate and emitter in the IGBT. The biggest difference at a fundamental level is how these semiconductor devices are driven, and this is a key consideration for the devices that switch them on and off, called gate drivers. A BJT is driven by current, whereas the MOSFET and IGBT are voltagedriven, which is why they have risen in popularity. A MOSFET can be n-channel or p-channel. The n-channel MOSFET is popular in applications such as AC-DC power supplies, DC-DC converters and inverter equipment, while the p-channel MOSFET is more often incorporated in load switches, high-side switches and other similar applications. the design of the power system and reducing the cost. However, designers want to use these newer power-transistor devices in the same way as MOSFETs and IGBTs, with the same chips that drive the gates of the transistors – the gate drivers. There are also devices that add a SiC or GaN diode to a MOSFET in a cascode configuration. This is a mid-range solution with less performance than a pure SiC MOSFET or GaN high-electron mobility transistor (HEMT), but it boosts performance, and in many cases it simplifies the design by being a drop-in replacement for a silicon MOSFET device. Packaging The choice of packaging has a big role to play in the losses experienced with power semiconductors. For inverters, mounting the bare die in a high-end module on a ceramic substrate to carry away heat is a suitable approach, while plastic modules are popular for mainstream applications with ready-built, half-bridge topologies for power conversion. Discrete packages can be used for designers who want to build their own systems. While so-called Kelvin packages add an extra fourth leg to reduce overall resistance, there are transistor outline leadless (TOLL) packages that also reduce RDS(on). For example, the 100 V automotivequalified OptiMOS silicon MOSFET devices from Infineon Technologies support currents up to 300 A with RDS(on) down to 0.77 mΩ. This makes it possible to reduce the number of parallel The range of gallium-nitride power devices (Image courtesy of EPC) A three-wheeler power-system design (Image courtesy of STMicroelectronics)
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