Table of Contents
Advertisement
Figure 8
Synchronous rectification control block diagram
2.4.1
On-time control - SRD pin and CL pin
With ICE2HS01's control scheme, SR MOSFET 's turning-off depends on two conditions - turning-off of
the primary gate and the "off" instruction from SR on-time block, where the maximum on-time
preset. Whichever "off" instruction comes first will trigger the turn-off of the SR MOSFET.
As illustrated in the previous chapter, the
converter operates below resonant frequency (
and the SR gate turn-on delay
a safe value as below:
1
<
−
T
T
_
max
on
DEAD
2
f
res
To achieve higher efficiency, a bigger
MOSFET conduction time and less body diode conduction time, which reduces conduction loss. In actual
design,
can be fine-tuned by looking at the similar waveforms in Figure 7, as long as safe
T
_
max
on
switching is guaranteed.
Application Note
T
_
max
on
f
( will be discussed later section 2.4.2), we can preset
T
_
on
delay
−
=
−
. 5
88
. 0
32
T
_
on
delay
is an advantage, because bigger on-time means longer SR
T
_
max
on
depends on the resonant frequency when LLC
<
)
. Considering the primary side dead time
f
sw
r
−
=
. 0
25
. 5
31
us
18
is
T
_
max
on
T
DEAD
with
T
_
max
on
[27]
2011-07-06
Advertisement
Table of Contents
