IEEE Power Electronics Magazine - September 2016 - 58

voltage MOSFET auxiliary switch,
One can use a regular MOSFET drivand custom control and drive IC in a
er, but the requirement to maintain
single package.
such a tightly limited range of gate
Sarda Technologies is also intevoltages will, in my opinion, dissuade
grating a wide-bandgap switching
many potential adopters even with
transistor and driver in a small, low
the very significant advantages GaN
parasitic package. Sarda, however,
Systems devices offer.
is unique in that it is using GaAs
There is a another variation of the
transistors, not GaN. The GaAs trancascode that has also been developed
sistors are also HEMTs and promise
and initially published in an applicavery high-speed switching (MHz) at
tion note by Infineon Technologies as
low loss. The limitation is that the
a drive technique for d-mode SiC
GaAs transistors, for the foreseeable
switches. In this circuit, there is a
future, will be limited to low-voltage
high-voltage d-mode GaN in series
(<100 V) applications, such as pointwith a low-voltage Si MOSFET. In this
of-load converters in server power.
arrangement, the MOSFET is held off
One key advantage to this approach
until a gate-drive circuit, powered by
is the very close coupling of the driver
some auxiliary power supply, starts
to the switch reducup a nd ca n sta r t
ing the gate-drive cirdriving the gate of
cuit parasitics to a
the d-mode device
The advantages of
level that is simply
with a small positive
combining the driver
not achievable on a
voltage to turn on
and the power switch
printed circuit board.
and a negative voltin the same package
Another advantage is
age (of say, −15 V) to
have been known for
the opportunity to
turn it off. Once the
include additional
a long time.
d-mode gate drive is
sensing and control
established, the Si
functions, such as
MOSFET is turned
overcurrent protection. I find these
on and held on. During operation, the
integrated driver/wide-bandgap switch
MOSFET does not switch. This proproducts very promising as a way
vides the advantages of the d-mode
to get the advantages of a wide-bandGaN device at the cost of the small
gap switch without a complex gate
on-resistance of the MOSFET-and a
drive circuit.
complicated control and drive for the
The advantages of combining the
d-mode device. However, since the
driver and the power switch in the
control and drive of the d-mode
same package have been known
device is most likely to be implementfor a long time. The "DR-MOS" or
ed in a vendor-specific gate drive IC
"DRMOS" combination of driver and
packaged with the MOSFET and GaN
silicon MOSFET has been available
switch, this complexity will be hidfor years. But what about going one
den from the user. The drive to the
step further and combining the drivswitch will be a simple logic level on-
er and the power switch on the same
off that is even easier than the standie-giving the ultimate reduction
dard MOSFET driver.
in gate drive parasitics?
I know of two companies that are
In general, this is not economical
using this kind of drive technique for
for Si MOSFETs and Si driver cirhigh-voltage d-mode GaN switches.
cuits. The processes used to make
The Texas Instruments LMG3410
the driver are more intensive and
GaN Power Stage is this kind of an
expensive than those used to make
auxiliary MOSFET to assure normalthe MOSFET. However, the MOSFET
ly off operation that gets turned on
takes up, by far, the most area on the
continuously while the GaN device is
die. This means that a large die is
switching. Visic Technologies has
being processed through a relatively
also developed products that inteexpensive process to add value to
grate a d-mode GaN switch, a low-

IEEE PowEr ElEctronIcs MagazInE

z September 2016

only a small part of the die. It has
been more economical, and the performance good enough, to copackage the driver and the MOSFET in
one package.
However, the conventional wisdom
is being challenged by the startup company Navitas Semiconductor. At this
year's Applied Power Electronics Conference and Exposition, Dan Kinzer,
Navitas' chief technology officer,
described an e-mode GaN switch and
driver circuit all on the same die. This
is to some the ideal combination, as it
is the absolute best one can do in eliminating parasitics from the gate-drive
circuit. I think this is a very exciting
development, and I will be watching
closely for further developments.
Since I am out of room, I will examine
the issues with driving the various SiC
switch types in my next column.

Disclaimer
The listing of companies and products
in this "White Hot" column is not an
endorsement of these companies or
their products by the IEEE or the
IEEE Power Electronics Society. I am
simply reporting on the companies
and products with which I have the
most experience.

About the Author
Robert V. White (bob.white@ieee.
org) has over 30 years of industry
experience as a power electronics
engineer. He has worked in product
design, systems and applications engineering, and technology development.
He has been an active volunteer with
the IEEE Power Electronics Society,
serving several years on the Administrative Committee, two terms as technical vice president, and as a Chapter
chair. He earned a B.S.E.E. degree
from the Massachusetts Institute of
Technology and an M.S.E.E. degree
from Worcester Polytechnic Institute.
He is currently pursuing a Ph.D.
degree in power electronics at the University of Colorado-Boulder. Presently, he is the chief engineer of Embedded Power Labs, a power electronics
consulting company. He is a Fellow of
the IEEE.

Table of Contents for the Digital Edition of IEEE Power Electronics Magazine - September 2016