The
rule
of
optimally-selected two-step frequency
switching
is
that starting
the converter
at
a high switching
frequency
(fstan)
which
is
slightly
less
then
than
the resonant
frequency
f,
in
order
to
obtain a
fast start-up
in
transient
state,
and
sensing
the
output voltage, the
switching frequency
will
be
switched
to
the
.frequency
(fief)
which
is corresponds
to
the
target
output
voltage
until
the
output
DC
voltage
reaches
about
90%
of
the target
voltage
VT.
Changing the switching
frequency
at the
90%
of
the
target
voltage
can effectively
decrease the chance overshooting the
target
voltage