FSQ0465RB View Datasheet(PDF) - Fairchild Semiconductor
Part Name
Description
MFG CO.
FSQ0465RB
Fairchild Semiconductor
'FSQ0465RB' PDF : 24 Pages View PDF
The switching frequency is the combination of blank time
(tB) and detection time window (tW). In case of a heavy
load, the sync voltage remains flat after tB and waits for
valley detection during tW. This leads to a low switching
frequency not suitable for heavy loads. To correct this
drawback, additional timing is used. The timing
conditions are described in Figures 25, 26, and 27. When
the Vsync remains flat higher than 4.4V at the end of tB
which is instant tX, the next switching cycle starts after
internal delay time from tX. In the second case, the next
switching occurs on the valley when the Vsync goes below
4.4V within tB. Once Vsync detects the first valley in tB, the
other switching cycle follows classical QRC operation.
tB=15µs
tX
tB=15µs
tX
IDS
IDS
VDS
ingnore
V sync
internal delay
4.4V
1.2V
1.0V
FSQ0465 Rev.00
IDS
IDS
VDS
Vsync
4.4V
1.2V
1.0V
internal delay
FSQ0465 Rev.00
Figure 25. Vsync > 4.4V at tX
tB=15µs
tX
IDS
IDS
VDS
Figure 27. After Vsync Finds First Valley
4. Protection Circuits: The FSQ-series has several
self-protective functions, such as Overload Protection
(OLP), Abnormal Over-Current Protection (AOCP),
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 VCC to fall. When VCC falls down to the
Under-Voltage Lockout (UVLO) stop voltage of 8V, the
protection is reset and the startup circuit charges the
VCC capacitor. When the VCC reaches the start voltage
of 12V, normal operation resumes. If the fault condition is
not removed, the SenseFET remains off and VCC drops
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.
VDS
Power
on
Fault
occurs
Fault
removed
Vsync
4.4V
1.2V
1.0V
internal delay
FSQ0465 Rev.00
Figure 26. Vsync < 4.4V at tX
VCC
12V
8V
t
FSQ0465 Rev.00
Normal
operation
Fault
situation
Normal
operation
Figure 28. Auto Restart Protection Waveforms
© 2008 Fairchild Semiconductor Corporation
FSQ0465RS/RB Rev. 1.0.1
13
www.fairchildsemi.com
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