Nexperia Creates a New FET Category: the Application-Specific FET (ASFET)

October 26, 2020 by Antonio Anzaldua Jr.

FETs and MOSFETs don't always cut it for dynamic applications. Nexperia says it has created a new flavor of FETs designed to rise to the challenge.

With applications pushing MOSFETs into unconventional designs, the testing parametric around these devices needs to move forward with the times. MOSFETs are increasingly GaN- and SiC-based due to their wide-bandgap, high-efficiency, and fast-switching capabilities. That said, these transistors are going to need better quality control testing.

Earlier this month, Nexperia introduced a new category of field-effect transistor (FET)—the application-specific FET (ASFET)—which will be structured as a standard MOSFET but with the added ability to anticipate dynamic applications. These applications might account for fast switching, higher power densities, and robust systems.


ASFETs for DC motor control

ASFETs for DC motor control can intake up to 300 A of inrush current, making it useful for high-torque start-up situations.


Nexperia anticipates that ASFETs will optimize performance for battery storage, motor control, power-over-internet (PoE), communication, and data-intensive applications.


What are ASFETs?

When a design requires transistors for switching and controlling elements (such as current), engineers turn to MOSFETs. But what happens when the design is meant to handle demanding parameters such as in-rush current?

Design engineers may need to add external components to anticipate this critical instance. This is what makes ASFETs appealing: they are designed for crucial situations that require smarter devices. 

Nexperia’s Senior Director of the Power MOSFETs Group, Chris Boyce, discussed how ASFETs are needed for the future of semiconductor advancements: “As designers push the boundaries of performance, it is crucial to understand how the MOSFET will be used in the application. There are 100+ parameters on a regular MOSFET datasheet but usually only a few are critical in each project. However, as the applications change, so do the critical parameters.”


A Few Use Cases of Application-Specific FETs

There are various parameters that make the application-specific FET family different from standard transistors. 

One application may be in data centers, where heavy data traffic passes through constantly. The overall system requires the protection of data and the power supply. Engineers are required to use integrated circuits that are designed to anticipate failures and prevent downtime.


Block diagram of ASFETs for battery isolation

ASFETs can operate safely and while be fully controllable until switched off, at which point, battery isolation occurs.


Nexperia’s ASFETs are said to offer enhanced protection during faults. The ASFETs for PoE can safely dissipate up to 30 W for 20 ms. ASFETs also allow hot-swapping to occur. This is when the system loses power or requires an update and needs to seamlessly switch to a standby system.


Block diagram of hot swap for communications infrastructure

Block diagram of hot-swap for communications infrastructure. 


Another parameter in which ASFETs can be used is for anticipating fault conditions such as in-rush current, an uncontrollable energy discharge that could lead to circuit burnouts. ASFETs are able to use a small voltage to control the increased current flow to prevent overheating. 

Aside from anticipating faults, current spikes, or potential downtime disruptions, ASFETs can handle repetitive avalanche currents in power inductive loads.


Nexperia’s ASFETs for repetitive avalanche

Nexperia’s ASFETs for repetitive avalanche are designed to reduce circuit complexity and cost by eliminating the need for additional parts. 


For driving solenoids in mechanical systems, design engineers will commonly use FETs to control switching by maintaining a steady flow of current. The issue is that FETs or low-side MOSFETs alone are not enough. Discrete components are needed to help drive the solenoid at a better performance.

Incorporating ASFETs will avoid additional components and will therefore simplify the overall design while saving manufacturers production time and costs.


FETs and MOSFETs Remain a Staple

Whether it be used for PoE, battery storage, or inductive systems, ASFETs are said to encourage faster, simpler, and more efficient designs. However, by no means does the ASFET take the place of an average FET or MOSFET, which are more versatile. 

At the moment, Nexperia’s ASFET covers a much narrower spectrum of use cases compared to a FET or MOSFET. For now, the cost-effective and time-saving route for amplification of a weak signal is still a FET. Similarly, MOSFETs are still a go-to for low-power applications.

But according to Boyce, engineers can expect to see the new ASFET family expand in the future. “We are continually seeking to deepen our understanding of specific applications, often working hand-in-hand with our customers," he explains.  

"In exposing our best engineers to detailed application requirements, we are opening new and exciting possibilities of innovation—there are many more ASFET advances in the pipeline.”


All images used courtesy of Nexperia