Page 54 - PEN eBook July 2023

Semiconductors
Figure 5: Self-turn-on effect in MOSFET bridge circuits
Figure 6: SCWT comparison of Rohm’s SiC MOSFET
54 JULY 2023 | www.powerelectronicsnews.com
Another important characteristic of
the fourth-generation trench design
is a markedly higher threshold
voltage. In a typical bridge circuit, as
shown in Figure 5, there is often the
danger of one MOSFET turning itself
on too fast, which causes the other
device to be accidentally turned on
as well due to parasitic C coupling.
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This can significantly increase losses
to the switching process because of
transient feed-through current. To
mitigate this effect, the MOSFETs
are often biased in the off state with
a dedicated negative voltage supply.
This additional supply increases
costs, complicates the design and
introduces a new potential failure
mode.
The higher threshold voltage of Rohm’s
fourth-generation SiC MOSFETs
facilitates reliable operation without
the added complexity of a negative
gate bias. Even at elevated junction
temperatures, the trench design
does not exhibit self-turn-on
tendencies during fast-switching
events.
The reliability of EV chargers is
paramount considering the high
voltages and currents involved. A
critical reliability metric for MOSFETs
in this application space is the
short-circuit withstand time (SCWT).
Rohm’s unique device structure in
its fourth-generation SiC MOSFETs
allowed for a lower saturation
current in spite of reduced specific