Low resistance 4mΩ SiC JFET for circuit breakers

Low resistance 4mΩ SiC JFET for circuit breakers

Technology News |
By Nick Flaherty

Qorvo has launched the industry’s first 4 milliohm silicon carbide (SiC) junction field effect transistor (JFET) in a standard TOLL leadless package.

The Qorvo 750V 4mΩ SiC JFET is designed for circuit protection applications including solid-state circuit breakers, where low resistance, superior thermal performance, small size and reliability are paramount.

The JFET technology was acquired with United SiC and is a ‘normally on’ technology, making it suitable for circuit breakers and the company is planning a 1200V version and one with integrated analog protection circuitry.

With an on resistance RDS(on) of just 4 milliohm, the UJ4N075004L8S offers the industry’s lowest on-resistance among the 650V to 750V class of power devices in standard discrete packages. This low RDS(on) drives significant reductions in heat generation and, when coupled with a compact TOLL package, enables a solution size that is 40% smaller than competing devices in TO-263 packages.

Qorvo buys UnitedSiC to expand into discrete power

This small footprint enables it to fit the space-limited dimensions of today’s electromechanical circuit breakers and operates without the need for a heat sink. This can accelerate the transition from electromechanical circuit breakers to semiconductor-based solid-state circuit breakers (SSCBs) says Qorvo.

“We typically put the JFETs in a cascode configuration to look like a MOSFET but we are starting to see areas where as standalone JFET has merits particularly in circuit protection,” said Andy Wilson product marketing and bus dev for JFETs for circuit protection.

“There’s been a lot of innovation in circuit breakers to resettable fuses but at the heart of all these systems is the same mechanical contact that has been there over 70 years and that has physical limitations in speed and under high currents for arcing. Moving to a solid state solution allows you to interrupt the current up to 100x faster so you don’t have as high currents and you completely eliminate the arc fault.”

However building a smart circuit breaker with a JFET still requires a Gate driver, microcontroller and connectivity. “This is very helpful for load management to remove load during peak loading situations, also with current monitoring,” said Wilson. “Right now the JFET can be driven with any off the shelf IGBT gate driver and we will have analog decision circuitry with a discrete cascode to overrule the microcontroller if it or the gate driver fails.”

“There are still are some major challenges facing designs of solid state circuit breakers, The dominant one is heat. These need to fit in existing panels alongside legacy electromechanical circuit breakers and there is no cooling. In a circuit panel you may have the majority will still be electromechanical with some semiconductor. They also need to tolerate an extremely current and turn that off successfully and that creates some very severe operating conditions.”

“As you can’t remove the heat the solution is to minimise the resistance, I2R, so everyone is looking for the lowest effective resistance with the minimal number of devices in parallel in compact packages with a robust technology.”

“The challenge for a SiC MOSFET with the gate oxide and MOS channel is that the channel has as significant resistance and to overcome that you need to increase the die size,” said Wilson. “The JFET doesn’t have a gate oxide so for the same die size we can have a much lower RDSon to addres the heat and size challenge. Not having the gate oxide helps with the robustness without any long term parametric drift.”

“There is one added function is that the Junction temp is proportional to the get leakage so this gives the actual device temperature rather than having a thermocouple sensor. This is something we get a lot of good feedback on.”

The UJ4N075004L8S is based around an existing 750V JFET developed for EV applications. “We have the ability to fit a larger die in the same package with lower resistance and with our Gen5 technology there are other innovations so there is absolutely room to  drive a reduction in the RDS(on) in the same footprint,” said Wilson.

“We will also be introducing a 1200V device but not in this TOLL package for the creepage clearance for 480V architectures.”

Fourth generation 1200V SiC FET for 800V designs

The UJ4N075004L8S is now available for sampling and will enter full production in Q4 2024, accompanied by additional JFET options, including 750V with 5 milliohm and 1200V with 8 milliohm ratings, all in TO-247 packaging.

Qorvo has a PCIM 2024 landing page.


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