Finding your high voltage power design sweet spot

  • May 09, 2022
  • UnitedSiC

When 750V Gen 4 SiC FETs were introduced back in 2020, the comparisons with Gen 3 at 650V were startling – 6 milliohm devices for example, showed near-halving of both the RDS•A figure of merit and the dynamic losses due to body diode reverse recovery energy. Turn-off energy Etot was substantially reduced, with short-circuit withstand time and body diode surge current also improved by more than 2x.

The improvements pushed the SiC FET further ahead of competing technologies; IGBTs, Si- and SiC- MOSFETs and even GaN, in systems where efficiency and cost are critical, such as in EV/solar inverters, battery chargers and PFC stages along with DC/DC and AC/DC conversion generally. The 750V rating was a useful added benefit over other devices in the applications, giving more safety margin over other technology devices typically rated at only 650V. This even allowed more efficiency savings with less lossy snubbing required to keep voltage overshoots within maximum ratings.

Devices at 1200V and higher ratings are available in Gen 3 technology and now UnitedSiC (now Qorvo) is making 1200V Gen 4 parts available in a selection of on-resistance ratings to suit a wide range of applications that typically use an 800V bus. For design flexibility, RDS(on) values of 23/30/53 and 70 milliohms are being offered, all in TO-247-4L packages with the extra Kelvin source connection for the fastest switching applications. The 53 and 70 milliohm parts are also available in the TO-247-3L package for less critical, more cost sensitive designs. As with the 750V parts, every device has industry-best figures of merit for conduction and dynamic related-losses RDS•A, RDS(on)•Coss,tr and RDS(on)•Qg. The 1200V parts also leverage techniques developed in Gen 4 – advanced cell maximization, wafer thinning technologies and silver-sinter die attach. This results in excellent thermal capabilities, matching the requirements of the higher power levels seen in higher bus voltage systems and the advanced cooling techniques utilized. The new UF4C/SC parts are optimized for hard switching applications such as the popular totem-pole PFC stage in continuous conduction mode. They are also well suited for soft-switched designs as well, where the low output capacitances and low conduction loss of the SiC FET are distinct advantages.

One of the obvious applications for the new 1200V parts is in EVs with 800V batteries, which require on-board chargers and auxiliary DC/DC converters. Of course, the new 1200V Gen 4 devices feature the established advantages of SiC FETs – normally off operation, easy gate drive, a low loss body diode and the inherent ruggedness of silicon carbide.

So, find your power design sweet spot with the new 1200V Gen 4 SiC FETs.