FSQ0565RS Fairchild Semiconductor, FSQ0565RS Datasheet - Page 13

• Manufacturer Part Number: FSQ0565RS
• Description: A Quasi-Resonant Converter (QRC) generally shows lower EMI and higher power conversion efficiency than a conventional hard-switched converter with a fixed switching frequency
• Manufacturer: Fairchild Semiconductor

FSQ0565RS/RQ Rev. 1.0.3
© 2008 Fairchild Semiconductor Corporation
The switching frequency is the combination of blank time
(t
load, the sync voltage remains flat after t
valley detection during t
frequency not suitable for heavy loads. To correct this
drawback, additional timing is used. The timing
conditions are described in Figures 26, 27, and 28. When
the V
which is instant t
internal delay time from t
switching occurs on the valley when the V
4.4V within t
other switching cycle follows classical QRC operation.
B
) and detection time window (t
sync
remains flat higher than 4.4V at the end of t
B
. Once V
Figure 26. V
Figure 27. V
I
I
DS
DS
X
t
t
B
B
, the next switching cycle starts after
=15µs
=15us
internal delay
internal delay
sync
V
V
W
sync
sync
X
V
. This leads to a low switching
V
detects the first valley in t
. In the second case, the next
sync
sync
DS
DS
< 4.4V at t
> 4.4V at t
W
t
t
X
X
). In case of a heavy
FSQ0565 Rev.00
FSQ 0565 Rev.00
sync
B
X
X
I
I
DS
and waits for
DS
4.4V
1.2V
1.0V
4.4V
1.2V
1.0V
goes below
B
, the
B
,
13
4. Protection Circuits: The FSQ-series has several
self-protective functions, such as Overload Protection
(OLP), Over-Voltage Protection (OVP), and Thermal
Shutdown (TSD). All the protections are implemented as
auto-restart mode. Once the fault condition is detected,
switching is terminated and the SenseFET remains off.
This causes V
Under-Voltage Lockout (UVLO) stop voltage of 8V, the
protection is reset and the startup circuit charges the
V
of 12V, normal operation resumes. If the fault condition is
not removed, the SenseFET remains off and V
to stop voltage again. In this manner, the auto-restart can
alternately enable and disable the switching of the power
SenseFET until the fault condition is eliminated.
Because these protection circuits are fully integrated into
the IC without external components, reliability is
improved without increasing cost.
CC
V
V
12V
Figure 29. Auto Restart Protection Waveforms
8V
FSQ0565 Rev.00
DS
CC
capacitor. When the V
Figure 28. After V
Power
I
on
D S
CC
operation
t
Norm al
B
=15us
to fall. When V
V
V
sync
DS
internal delay
occurs
Fault
sync
ingnore
situation
CC
Fault
Finds First Valley
reaches the start voltage
t
X
rem oved
CC
Fault
falls down to the
I
FS Q 0565 R ev.00
DS
operation
www.fairchildsemi.com
4.4V
Norm al
1.2V
1.0V
CC
drops
t