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With
< 0.4V,
V
V
CS
CL
SR on time is reduced with the load decreased.
For filter purpose,
C
CL
Figure 10
SR on time versus SRD resistance
2.4.2
Turn-on delay
When the input voltage is higher than resonant voltage, the LLC converter secondary switches are
working in CCM condition. Certain recovery time of the SR MOSFET body diode is required depending on
the current to turn-off. For better performance, the other SR MOSFET should be turn on after the
recovery phase. The turn-on delay function is built in ICE2HS01G for such purpose. When the sensed
input voltage at VINS pin is higher than the reference voltage set by Vres pin according to the resonant
voltage, SR turn-on delay is added, i.e, the SR MOSFETs are turn on 250ns after the corresponding
primary MOSFETs are turned on.
The nominal bus voltage at resonant point is:
=
+
2
( *
)
V
n
V
V
res
O
f
The corresponding voltage at VINS pin is 1.59V. To allow the turn-on delay for input voltage above this
resonant point, we can set the voltage divider
=
Ω
12
select
, and
R
k
1
res
operation, we can set the voltage at
=
Ω
6
2 .
and
.
R
k
2
res
Application Note
starts to drop below 2V, extra current is drawn from SRD pin, thereby the actual
is chosen to be 47nF.
T
- Vres pin
_
on
delay
=
+
2
*
16
5 .
( *
12
0
) 1 .
R
can be calculated to be 5.2kΩ. To disable the turn-on delay during normal
R
2
res
to be 1.07x1.59=1.7V. Accordingly,
V
res
=
399
3 .
V
and
connected at VRES pin accordingly. We
R
1
2
res
res
20
=
Ω
12
,
R
k
1
res
2011-07-06
[28]
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