Page 60 - PEN eBook July 2023

Test & Measurement

In recent years, wide-bandgap (WBG) devices have made significant progress in replacing
silicon-based power MOSFETs and IGBTs in many power-related applications. Their fundamental
characteristics enable significant improvements in key areas for power applications. When

comparing GaN with silicon, it is well known that GaN’s higher bandgap, higher electron mobility
and larger electric-field potential enable important attributes, such as lower losses (i.e., higher
efficiency), faster switching and a significantly reduced size (i.e., higher power density). However,
WBG devices have a much shorter history of use in a variety of power applications compared with
silicon, especially “high uptime” applications like automotive.

JEDEC formed the JC-70 Committee in 2017 to develop needed new reliability, characterization,
test methods and datasheet enhancements to appropriately characterize GaN and SiC WBG power
devices. The existing Si-based standards were not sufficient to enable designers to determine

the most appropriate WBG devices for their application. For example, on-resistance (R ), the
DS(on)
main parameter characterizing conduction losses, is a dynamic phenomenon in GaN, based on
the charge being trapped in the transistor structure (current collapse). JEP-173 was JC-70’s first
publication (issued in January 2019) to provide a standard for “dynamic on-resistance test method
guidelines for GaN HEMT–based power-conversion devices.”

EXAMPLES OF LOW-VOLTAGE GaN FET APPLICATIONS

One application of the initial Class D audio amplifiers was sound systems for automobiles. The
amplifier’s lower power dissipation and superior efficiency (>90%), compared with Class A amplifiers,
enabled “limited power” automobiles the ability to have multiple speakers and more sound (>100 W).
However, the tradeoff for less power consumption was higher total harmonic distortion (THD),
created by slower-switching power Si MOSFETs. GaN FETs with significantly faster switching speeds
(up to 10×) and no reverse-recovery charge provide a superior linear response and significantly
reduced THD.

In addition to automotive applications, you’ve probably noticed the recent boom in portable

speakers. As well as advances in battery technology, this application is enabled by efficient,
compact Class D audio amplifiers designed with GaN FETs. Good audio quality is provided because
of the lower-distortion attributes of GaN, while the ability to run for extended times on batteries
is possible because of GaN’s high efficiency. There are many other portable consumer devices that
can leverage the same attributes as portable speakers.

Automotive systems are moving toward higher-voltage operation (e.g., 48 V) as more electrical

power needs develop for autonomous driving, including radar, cameras, ultrasonic sensors and
LiDAR. These functions require uninterrupted, highly reliable power. As the 48-V bus emerges as
one of the new higher-voltage power systems, efficiency is again the key with a limited power
source (i.e., car battery). GaN technology enables better power density than silicon, minimizing
additional weight, size and thermal management. GaN’s higher-frequency switching and increased

60 JULY 2023 | www.powerelectronicsnews.com