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FSCQ-Series:
FSCQ0565RT / FSCQ0765RT / FSCQ0965RT / FSCQ1265RT / FSCQ1565RT
Green Mode Fairchild Power Switch (FPS™)
Features
Description
Optimized for Quasi-Resonant Converter (QRC)
Pulse-by-Pulse Current Limit
A Quasi-Resonant Converter (QRC) typically shows
lower EMI and higher power conversion efficiency
compared to a conventional hard-switched converter
with a fixed switching frequency. Therefore, a QRC is
well suited for noise-sensitive applications, such as
color TV and audio. Each product in the FSCQ series
contains an integrated Pulse Width Modulation (PWM)
controller and a SenseFET. This series is specifically
designed for quasi-resonant off-line Switch Mode Power
Supplies (SMPS) with minimal external components.
The PWM controller includes an integrated fixed
frequency oscillator, under-voltage lockout, leadingedge blanking (LEB), optimized gate driver, internal softstart, temperature-compensated precise current sources
for loop compensation, and self-protection circuitry.
Compared with a discrete MOSFET and PWM controller
solution, the FSCQ series can reduce total cost,
component count, size, and weight; while increasing
efficiency, productivity, and system reliability. These
devices provide a basic platform for cost-effective
designs of quasi-resonant switching flyback converters.
Advanced Burst-Mode Operation for under 1 W
Standby Power Consumption
Overload Protection (OLP) – Auto Restart
Over-Voltage Protection (OVP) – Auto Restart
Abnormal Over-Current Protection (AOCP) – Latch
Internal Thermal Shutdown (TSD) – Latch
Under-Voltage Lockout (UVLO) with Hysteresis
Low Startup Current (Typical: 25 μA)
Internal High Voltage SenseFET
Built-in Soft-Start (20 ms)
Extended Quasi-Resonant Switching
Applications
CTV
Audio Amplifier
Related Resources
AN-4146 — Design Guidelines for Quasi-Resonant Converters Using FSCQ-Series Fairchild Power Switch
AN-4140 — Transformer Design Consideration for Offline Flyback Converters Using Fairchild Power Switch
Ordering Information
Part Number
Package
Marking Code
BVDSS (V)
RDSON Max. (Ω)
FSCQ0565RTYDTU
TO-220F-5L (Forming)
CQ0565RT
650
2.2
FSCQ0765RTYDTU
TO-220F-5L (Forming)
CQ0765RT
650
1.6
FSCQ0965RTYDTU
TO-220F-5L (Forming)
CQ0965RT
650
1.2
FSCQ1265RTYDTU
TO-220F-5L (Forming)
CQ1265RT
650
0.9
FSCQ1565RTYDTU
TO-220F-5L (Forming)
CQ1565RT
650
0.7
© 2006 Fairchild Semiconductor Corporation
FSQ-Series • Rev. 1.1.3
www.fairchildsemi.com
FSCQ-Series — Green Mode Fairchild Power Switch (FPS™)
January 2014
FSCQ-Series — Green Mode Fairchild Power Switch (FPS™)
Typical Circuit
VO
AC
IN
FSCQ-Series
Drain
PWM
Sync
GND
VCC
VFB
Figure 1.
Table 1.
Maximum Output Power
Typical Flyback Application
(1)
230 VAC ±15%(2)
Product
Open Frame
(3)
85–265 VAC
Open Frame(3)
FSCQ0565RT
70 W
60 W
FSCQ0765RT
100 W
85 W
FSCQ0965RT
130 W
110 W
FSCQ1265RT
170 W
140 W
FSCQ1565RT
210 W
170 W
Notes:
1. The junction temperature can limit the maximum output power.
2. 230 VAC or 100/115 VAC with doubler.
3. Maximum practical continuous power in an open frame design at 50C ambient.
© 2006 Fairchild Semiconductor Corporation
FSQ-Series • Rev. 1.1.3
www.fairchildsemi.com
2
Sync
5
Vcc
3
Drain
1
+
Threshold
Quasi-Resonant
(QR) Switching
Controller
-
+
fs
-
Soft Start
4.6V/2.6V : Normal QR
3.0V/1.8V : Extended QR
Burst Mode
Controller
VBurst
Normal Operation
Vref
IBFB
Vcc good
Auxiliary
Vref
OSC
Burst Switching
Vref
Main Bias
Normal
Operation
Vref
IFB
9V/15V
Internal
Bias
IB
Vcc
Idelay
VFB
PWM
4
2.5R
S
Q
R
Q
Gate
Driver
R
LEB
600ns
VSD
Sync
Vovp
S
Vcc good
(Vcc = 9V)
R
Q
Q
AOCP
Q
S
Q
R
2 GND
TSD
Vocp
Power Off Reset (Vcc = 6V)
Figure 2.
© 2006 Fairchild Semiconductor Corporation
FSQ-Series • Rev. 1.1.3
Functional Block Diagram
www.fairchildsemi.com
3
FSCQ-Series — Green Mode Fairchild Power Switch (FPS™)
Internal Block Diagram
Figure 3.
5
SYNC
4
VFB
3
VCC
2
GND
1
DRAIN
Pin Assignments (Top View)
Pin Descriptions
Pin
Name
Description
1
DRAIN
2
GND
This pin is the control ground and the SenseFET source.
3
VCC
This pin is the positive supply input. This pin provides internal operating current for both startup
and steady-state operation.
4
VFB
This pin is internally connected to the inverting input of the PWM comparator. The collector of an
opto-coupler is typically tied to this pin. For stable operation, a capacitor should be placed
between this pin and GND. If the voltage of this pin reaches 7.5 V, the overload protection
triggers, which results in the FPS™ shutting down.
5
SYNC
This pin is internally connected to the sync detect comparator for quasi-resonant switching. In
normal quasi-resonant operation, the threshold of the sync comparator is 4.6 V / 2.6 V. Whereas,
the sync threshold is changed to 3.0 V / 1.8 V in an extended quasi-resonant operation.
This pin is the high-voltage power SenseFET drain connection.
© 2006 Fairchild Semiconductor Corporation
FSQ-Series • Rev. 1.1.3
www.fairchildsemi.com
4
FSCQ-Series — Green Mode Fairchild Power Switch (FPS™)
Pin Configuration
Stresses exceeding the absolute maximum ratings may damage the device. The device may not function or be
operable above the recommended operating conditions and stressing the parts to these levels is not recommended.
In addition, extended exposure to stresses above the recommended operating conditions may affect device reliability.
The absolute maximum ratings are stress ratings only. TA = 25°C, unless otherwise specified.
Symbol
Parameter
Value
Unit
VDS
Drain Pin Voltage
650
V
VCC
Supply Voltage
20
V
Vsync
VFB
IDM
ID
ID*
ID
EAS
PD
Drain Current Pulsed
-0.3 to VCC
(4)
Continuous Drain Current (TC = 25°C)
(TC: Case Back Surface Temperature)
Continuous Drain Current* (TDL = 25°C)
(TDL: Drain Lead Temperature)
Continuous Drain Current (TC = 100°C)
Single-Pulsed Avalanche Energy
(5)
Total Power Dissipation (TC = 25°C with Infinite Heat Sink)
TJ
Operating Junction Temperature
TA
TSTG
-0.3 to 13
Analog Input Voltage Range
FSCQ0565RT
11.2
FSCQ0765RT
15.2
FSCQ0965RT
16.4
FSCQ1265RT
21.2
FSCQ1565RT
26.4
FSCQ0565RT
2.8
FSCQ0765RT
3.8
FSCQ0965RT
4.1
FSCQ1265RT
5.3
FSCQ1565RT
6.6
FSCQ0565RT
5.0
FSCQ0765RT
7.0
FSCQ0965RT
7.6
FSCQ1265RT
11.0
FSCQ1565RT
13.3
FSCQ0565RT
1.7
FSCQ0765RT
2.4
FSCQ0965RT
2.6
FSCQ1265RT
3.4
FSCQ1565RT
4.4
FSCQ0565RT
400
FSCQ0765RT
570
FSCQ0965RT
630
FSCQ1265RT
950
FSCQ1565RT
1050
FSCQ0565RT
38
FSCQ0765RT
45
FSCQ0965RT
49
FSCQ1265RT
50
FSCQ1565RT
75
V
A
A(rms)
A(rms)
A(rms)
mJ
W
150
°C
Operating Ambient Temperature
-25 to +85
°C
Storage Temperature Range
-55 to +150
°C
Continued on the following page…
© 2006 Fairchild Semiconductor Corporation
FSQ-Series • Rev. 1.1.3
www.fairchildsemi.com
5
FSCQ-Series — Green Mode Fairchild Power Switch (FPS™)
Absolute Maximum Ratings
Stresses exceeding the absolute maximum ratings may damage the device. The device may not function or be
operable above the recommended operating conditions and stressing the parts to these levels is not recommended.
In addition, extended exposure to stresses above the recommended operating conditions may affect device reliability.
The absolute maximum ratings are stress ratings only. TA = 25°C, unless otherwise specified.
Symbol
ESD
Parameter
Value
Unit
Human Body Model (All Pins Except VFB)
(GND – VFB = 1.7 kV)
2.0
kV
Machine Model (All Pins Except VFB)
(GND – VFB = 170 V)
300
V
Notes:
4. Repetitive rating: pulse width limited by maximum junction temperature.
5. L = 15 mH, starting TJ = 25°C. These parameters, although guaranteed by design, are not tested in production.
Thermal Impedance
TA = 25°C unless otherwise specified.
Symbol
JC
Parameter
Junction-to-Case Thermal Impedance
© 2006 Fairchild Semiconductor Corporation
FSQ-Series • Rev. 1.1.3
Value
FSCQ0565RT
3.29
FSCQ0765RT
2.60
FSCQ0965RT
2.55
FSCQ1265RT
2.50
FSCQ1565RT
2.00
Unit
°C/W
www.fairchildsemi.com
6
FSCQ-Series — Green Mode Fairchild Power Switch (FPS™)
Absolute Maximum Ratings
TA= 25°C unless otherwise specified.
Symbol
Parameter
Condition
Min. Typ. Max. Unit
SenseFET Part
BVDSS
Drain-Source Breakdown Voltage
VGS = 0 V, ID = 250 μA
IDSS
Zero Gate Voltage Drain Current
VDS = 650 V,VGS = 0 V
RDS(ON)
Drain-Source On-State Resistance
650
250
FSCQ0565RT
VGS = 10 V, ID = 1 A
1.76
2.20
FSCQ0765RT
VGS = 10 V, ID = 1 A
1.40
1.60
FSCQ0965RT
VGS = 10 V, ID = 1 A
1.00
1.20
FSCQ1265RT
VGS = 10 V, ID = 1 A
0.75
0.90
FSCQ1565RT
VGS = 10 V, ID = 1 A
0.53
0.70
FSCQ0565RT
Input Capacitance
FSCQ0965RT
Output Capacitance
1750
FSCQ1265RT
2400
FSCQ1565RT
3050
FSCQ0565RT
90
FSCQ0965RT
Ω
1415
VGS = 0 V, VDS = 25 V,
f = 1 MHz
FSCQ0765RT
COSS
μA
1080
FSCQ0765RT
CISS
V
pF
100
VGS = 0 V, VDS = 25 V,
f = 1 MHz
130
FSCQ1265RT
175
FSCQ1565RT
220
pF
Control Section
fOSC
ΔfOSC
IFB
Switching Frequency
VFB = 5 V, VCC = 18 V
18
20
22
kHz
Switching Frequency Variation
-25°C ≤ TA ≤ 85°C
0
±5
±10
%
0.65
0.80
mA
95
98
%
(7)
Feedback Source Current
VFB = 0.8 V, VCC = 18 V 0.50
DMAX
Maximum Duty Cycle
VFB = 5 V, VCC = 18 V
DMIN
Minimum Duty Cycle
VFB = 0 V, VCC = 18 V
UVLO Threshold Voltage
VFB = 1 V
VSTART
VSTOP
tSS
Soft-Start Time
(6)
92
0
%
14
15
16
8
9
10
18
20
22
V
ms
Burst Mode Section
VBEN
Burst Mode Enable Feedback Voltage
0.25
0.40
0.55
V
IBFB
Burst Mode Feedback Source Current
VFB = 0 V
60
100
140
μA
tBS
Burst Mode Switching Time
VFB = 0.9 V,
Duty = 50%
1.2
1.4
1.6
ms
tBH
Burst Mode Hold Time
VFB = 0.9 V → 0 V
1.2
1.4
1.6
ms
Protection Section
Shutdown Feedback Voltage
VCC = 18 V
7.0
7.5
8.0
V
IDELAY
VSD
Shutdown Delay Current
VFB = 5 V, VCC = 18 V
4
5
6
μA
VOVP
Over-Voltage Protection
VFB = 3 V
11
12
13
V
VCC = 18 V
0.9
1.0
1.1
V
VOCL
TSD
Over-Current Latch Voltage
(6)
Thermal Shutdown Temperature
(7)
140
°C
Continued on the following page…
© 2006 Fairchild Semiconductor Corporation
FSQ-Series • Rev. 1.1.3
www.fairchildsemi.com
7
FSCQ-Series — Green Mode Fairchild Power Switch (FPS™)
Electrical Characteristics
TA= 25°C unless otherwise specified.
Symbol
Parameter
Condition
Min. Typ. Max. Unit
Sync Section
VSH1
Sync Threshold in Normal QR (H)
4.2
4.6
5.0
V
VSL1
Sync Threshold in Normal QR (L)
2.3
2.6
2.9
V
VSH2
Sync Threshold in Extended QR (H)
2.7
3.0
3.3
V
VSL2
Sync Threshold in Extended QR (L)
1.6
1.8
2.0
V
fSYH
Extended QR Enable Frequency
90
kHz
fSYL
Extended QR Disable Frequency
45
kHz
VCC = 18 V, VFB = 5 V
Total Device Section
IOP
IOB
ISTART
ISN
Operating Supply Current in
(8)
Normal Operation
FSCQ0565RT
4
6
FSCQ0765RT
4
6
FSCQ0965RT
6
8
FSCQ1265RT
VFB = 5 V
6
8
mA
FSCQ1565RT
7
9
0.25
0.50
mA
Operating Supply Current in Burst Mode (Non(8)
Switching)
VFB = GND
Startup Current
VCC = VSTART – 0.1 V
25
50
μA
VCC = VSTOP – 0.1 V
50
100
μA
Sustain Latch Current
(6)
Current Sense Section
ILIM
IBUR(pk)
Maximum Current Limit
Burst Peak Current
(9)
FSCQ0565RT
3.08
3.50
3.92
FSCQ0765RT
4.40
5.00
5.60
FSCQ0965RT
5.28
6.00
6.72
FSCQ1265RT
6.16
7.00
7.84
FSCQ1565RT
7.04
8.00
8.96
FSCQ0565RT
0.45
0.65
0.85
FSCQ0765RT
0.65
0.90
1.15
0.60
0.90
1.20
0.80
1.20
1.60
FSCQ0965RT
VCC = 18 V, VFB = 5 V
VCC = 18 V, VFB = Pulse
FSCQ1265RT
FSCQ1565RT
A
A
1.00
Notes:
6. These parameters, although guaranteed, are tested only in wafer test process.
7. These parameters, although guaranteed by design, are not tested in production.
8. This parameter is the current flowing in the control IC.
9. These parameters indicate inductor current.
10. These parameters, although guaranteed, are tested only in wafer test process.
© 2006 Fairchild Semiconductor Corporation
FSQ-Series • Rev. 1.1.3
www.fairchildsemi.com
8
FSCQ-Series — Green Mode Fairchild Power Switch (FPS™)
Electrical Characteristics
Figure 4.
Operating Supply Current
Figure 6.
Figure 8.
Figure 5.
Startup Current
Figure 7.
Stop Threshold Voltage
© 2006 Fairchild Semiconductor Corporation
FSQ-Series • Rev. 1.1.3
Burst Mode Supply Current
(Non-Switching)
Figure 9.
Start Threshold Voltage
Initial Frequency
www.fairchildsemi.com
9
FSCQ-Series — Green Mode Fairchild Power Switch (FPS™)
Typical Performance Characteristics
Figure 10.
Maximum Duty Cycle
Figure 12.
Shutdown Delay Current
Figure 14.
Feedback Source Current
© 2006 Fairchild Semiconductor Corporation
FSQ-Series • Rev. 1.1.3
Figure 11.
Figure 13.
Figure 15.
Over-Voltage Protection
Shutdown Feedback Voltage
Burst Mode Feedback Source Current
www.fairchildsemi.com
10
FSCQ-Series — Green Mode Fairchild Power Switch (FPS™)
Typical Performance Characteristics
Figure 16.
Figure 18.
Figure 20.
Feedback Offset Voltage
Figure 17.
Sync. Threshold in Normal QR(H)
Figure 19.
Sync. Threshold in Extended QR(H)
© 2006 Fairchild Semiconductor Corporation
FSQ-Series • Rev. 1.1.3
Figure 21.
Burst Mode Enable Feedback Voltage
Sync. Threshold in Normal QR(L)
Sync. Threshold in Extended QR(L)
www.fairchildsemi.com
11
FSCQ-Series — Green Mode Fairchild Power Switch (FPS™)
Typical Performance Characteristics
Figure 22.
Figure 24.
Extended QR Enable Frequency
Figure 23.
Extended QR Disable Frequency
Pulse-by-Pulse Current Limit
© 2006 Fairchild Semiconductor Corporation
FSQ-Series • Rev. 1.1.3
www.fairchildsemi.com
12
FSCQ-Series — Green Mode Fairchild Power Switch (FPS™)
Typical Performance Characteristics
1. Startup: Figure 25 shows the typical startup circuit
and the transformer auxiliary winding for the FSCQ
series. Before the FSCQ series begins switching, it
consumes only startup current (typically 25 μA). The
current supplied from the AC line charges the external
capacitor (Ca1) that is connected to the VCC pin. When
VCC reaches the start voltage of 15 V (VSTART), the
FSCQ series begins switching and its current
consumption increases to IOP. Then, the FSCQ series
continues normal switching operation and the power
required is supplied from the transformer auxiliary
winding, unless VCC drops below the stop voltage of 9 V
(VSTOP). To guarantee stable operation of the control IC,
VCC has under-voltage lockout (UVLO) with 6 V
hysteresis. Figure 26 shows the relationship between
the operating supply current of the FSCQ series and the
supply voltage (VCC).
The minimum average of the current supplied from the
AC is given by:
ISUP
2 V MIN
V
AC
START
2
AVG
1
R
STR
(1)
min
where Vac is the minimum input voltage, VSTART is
the FSCQ series’ start voltage (15 V), and Rstr is the
startup resistor. The startup resistor should be chosen
avg
so that Isup is larger than the maximum startup
current (50 μA).
Once the resistor value is determined, the maximum
loss in the startup resistor is obtained as:
Loss
RSTR
where Vac
CDC
2
MAX
V MAX 2 V
2 2 VSTART VAC
START
AC
2
1
max
is the maximum input voltage.
The startup resistor should have properly
dissipation wattage.
Isup
Rstr
Da
VCC
FSCQ-Series
Ca2
Ca1
Figure 25.
CDC
Startup Circuit
+
VDC
-
Np
Ns
Lm
ICC
rated
2. Synchronization: The FSCQ series employs a
quasi-resonant switching technique to minimize the
switching noise and loss. In this technique, a capacitor
(Cr) is added between the MOSFET drain and the
source, as shown in Figure 27. The basic waveforms of
the quasi-resonant converter are shown in Figure 28.
The external capacitor lowers the rising slope of the
drain voltage to reduce the EMI caused when the
MOSFET turns off. To minimize the MOSFET’s
switching loss, the MOSFET should be turned on when
the drain voltage reaches its minimum value, as shown
in Figure 28.
1N4007
AC line
(Vacmin - Vacmax)
(2)
Vo
IOP Value
FSCQ0565RT: 4mA (Typ.)
FSCQ0765RT: 4mA (Typ.)
FSCQ0965RT: 6mA (Typ.)
FSCQ1265RT: 6mA (Typ.)
FSCQ1565RT: 7mA (Typ.)
Drain
Cr
Ids
Sync
+
Vds
-
GND
IOP
Vco
Vcc
Rcc
Power Up
Power Down
Ca1
ISTART
Ca2
Na
DSY
VCC
VSTOP=9V
Figure 26.
Da
VSTART=15V
VZ
RSY1
Relationship between Operating Supply
Current and VCC Voltage
CSY
Figure 27.
© 2006 Fairchild Semiconductor Corporation
FSQ-Series • Rev. 1.1.3
RSY2
Synchronization Circuit
www.fairchildsemi.com
13
FSCQ-Series — Green Mode Fairchild Power Switch (FPS™)
Functional Description
Vds
Vgs
2VRO
VRO
VRO
Vds
tQ
Vsync
VDC
Vsypk
Vrh (4.6V)
Ids
Vrf (2.6V)
Ipk
tR
MOSFET Gate
Figure 28.
Quasi-Resonant Operation Waveforms
The minimum drain voltage is indirectly detected by
monitoring the VCC winding voltage, as shown in Figure
27 and Figure 29. Choose voltage dividers, RSY1 and
RSY2, so that the peak voltage of the sync signal (V sypk)
is lower than the OVP voltage (12 V) to avoid triggering
OVP in normal operation. It is typical to set Vsypk to be
lower than OVP voltage by 3–4 V. To detect the
optimum time to turn on MOSFET, the sync capacitor
(CSY) should be determined so that tR is the same with
tQ, as shown in Figure 29. The tR and tQ are given as:
t R RSY 2 CSY
V
RSY 2
In CO
2
.
6
R
SY 1 RSY 2
tQ Lm Ceo
VCO
Na VO VFO
VFa
Ns
ON
Figure 29.
ON
Normal QR Operation Waveforms
Switching
Frequency
Extended QR
Operation
90kHz
(3)
Normal QR
Operation
45kHz
(4)
(5)
Output Power
where:
Figure 30.
Lm is the primary side inductance of the transformer;
In general, the QRC has a limitation in a wide load
range application, since the switching frequency
increases as the output load decreases, resulting in a
severe switching loss in the light load condition. To
overcome this limitation, the FSCQ series employs an
extended quasi-resonant switching operation. Figure 30
shows the mode change between normal and extended
quasi-resonant operations. In the normal quasi-resonant
operation, the FSCQ series enters into the extended
quasi-resonant operation when the switching frequency
exceeds 90 kHz as the load reduces. To reduce the
switching frequency, the MOSFET is turned on when
the drain voltage reaches the second minimum level, as
shown in Figure 31. Once the FSCQ series enters into
the extended quasi-resonant operation, the first sync
signal is ignored. After the first sync signal is applied,
the sync threshold levels are changed from 4.6 V and
2.6 V to 3 V and 1.8 V, respectively, and the MOSFET
turn-on time is synchronized to the second sync signal.
The FSCQ series returns to its normal quasi-resonant
operation when the switching frequency reaches 45 kHz
as the load increases.
Ns is the number of turns for the output winding;
Na is the number of turns for the VCC winding;
VFo is the diode forward-voltage drop of the output
winding;
VFa is the diode forward-voltage drop of the VCC
winding; and
Ceo is the sum of the output capacitance of the
MOSFET and the external capacitor, Cr.
© 2006 Fairchild Semiconductor Corporation
FSQ-Series • Rev. 1.1.3
Extended Quasi-Resonant Operation
www.fairchildsemi.com
14
FSCQ-Series — Green Mode Fairchild Power Switch (FPS™)
MOSFET
On
MOSFET
Off
VCC
Vref
Idelay
2VRO
Vfb
VO
IFB
4
H11A817A
D2
2.5R
+
Vfb*
KA431
VSD
3V
2.6V
Figure 32.
OLP
Rsense
Pulse Width Modulation (PWM) Circuit
1.8V
4. Protection Circuits: The FSCQ series has several
self-protective functions such as overload protection
(OLP), abnormal over-current protection (AOCP), overvoltage protection (OVP), and thermal shutdown (TSD).
OLP and OVP are auto-restart mode protections, while
TSD and AOCP are latch mode protections. Because
these protection circuits are fully integrated into the IC
without external components, the reliability can be
improved without increasing cost.
MOSFET Gate
ON
Figure 31.
Gate
Driver
R
-
Vsyn
c
4.6V
SenseFET
OSC
D1
CB
ON
Extended QR Operation Waveforms
3. Feedback Control: The FSCQ series employs
current mode control, as shown in Figure 32. An optocoupler (such as Fairchild’s H11A817A) and shunt
regulator (such as Fairchild’s KA431) are typically used
to implement the feedback network. Comparing the
feedback voltage with the voltage across the Rsense
resistor, plus an offset voltage, makes it possible to
control the switching duty cycle. When the reference pin
voltage of the shunt regulator exceeds the internal
reference voltage of 2.5 V, the opto-coupler LED current
increases, pulling down the feedback voltage and
reducing the duty cycle. This typically occurs when input
voltage is increased or output load is decreased.
3.1 Pulse-by-Pulse Current Limit: Because current
mode control is employed, the peak current through the
SenseFET is limited by the inverting input of the PWM
comparator (Vfb*) as shown in Figure 32. The feedback
current (IFB) and internal resistors are designed so that
the maximum cathode voltage of diode D2 is about
2.8 V, which occurs when all IFB flows through the
internal resistors. Since D1 is blocked when the
feedback voltage (Vfb) exceeds 2.8 V, the maximum
voltage of the cathode of D2 is clamped at this voltage,
thus clamping Vfb*. Therefore, the peak value of the
current through the SenseFET is limited.
-
Auto-Restart Mode Protection: Once the fault
condition is detected, switching is terminated and
the SenseFET remains off. This causes VCC to fall.
When VCC falls to the under voltage lockout (UVLO)
stop voltage of 9 V, the protection is reset and the
FSCQ series consumes only startup current
(25 μA). Then, the VCC capacitor is charged up,
since the current supplied through the startup
resistor is larger than the current that the FPS
consumes. When VCC reaches the start voltage of
15 V, the FSCQ series resumes its normal
operation. 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 (see Figure 33).
-
Latch Mode Protection: Once this protection is
triggered, switching is terminated and the
SenseFET remains off until the AC power line is
unplugged. Then, VCC continues charging and
discharging between 9 V and 15 V. The latch is
reset only when VCC is discharged to 6 V by
unplugging the AC power line.
3.2 Leading Edge Blanking (LEB): At the instant the
internal SenseFET is turned on, there is usually a high
current spike through the SenseFET, caused by the
external resonant capacitor across the MOSFET and
secondary-side rectifier reverse recovery. Excessive
voltage across the Rsense resistor can lead to incorrect
feedback operation in the current mode PWM control.
To counter this effect, the FSCQ series employs a
leading edge blanking (LEB) circuit. This circuit inhibits
the PWM comparator for a short time (tLEB) after the
Sense FET is turned on.
© 2006 Fairchild Semiconductor Corporation
FSQ-Series • Rev. 1.1.3
www.fairchildsemi.com
15
FSCQ-Series — Green Mode Fairchild Power Switch (FPS™)
Vds
4.2 Abnormal Over Current Protection (AOCP):
When the secondary rectifier diodes or the transformer
pins are shorted, a steep current with extremely high
di/dt can flow through the SenseFET during the LEB
time. Even though the FSCQ series has OLP (Overload
Protection), it is not enough to protect the FSCQ series
in that abnormal case, since severe current stress will
be imposed on the SenseFET until the OLP triggers.
The FSCQ series has an internal AOCP (Abnormal
Over-Current Protection) circuit as shown in Figure 35.
When the gate turn-on signal is applied to the power
SenseFET, the AOCP block is enabled and monitors the
current through the sensing resistor. The voltage across
the resistor is then compared with a preset AOCP level.
If the sensing resistor voltage is greater than the AOCP
level, the set signal is applied to the latch, resulting in
the shutdown of SMPS. This protection is implemented
in the latch mode.
Fault
removed
Vcc
15V
9V
ICC
IOP
ISTART
2.5R
t
Normal
operation
Figure 33.
Fault
situation
OSC
Normal
operation
PWM
Auto Restart Mode Protection
4.1 Overload Protection (OLP): Overload is defined as
the load current exceeding its normal level due to an
unexpected abnormal event. In this situation, the
protection circuit should trigger to protect the SMPS.
However, even when the SMPS is in the normal
operation, the over load protection circuit can be
triggered during the load transition. To avoid this
undesired operation, the overload protection circuit is
designed to trigger after a specified time to determine
whether it is a transient situation or an overload
situation. Because of the pulse-by-pulse current limit
capability, the maximum peak current through the
SenseFET is limited, and therefore the maximum input
power is restricted with a given input voltage. If the
output consumes more than this maximum power, the
output voltage (Vo) decreases below the set voltage.
This reduces the current through the opto-coupler LED,
which also reduces the opto-coupler transistor current,
thus increasing the feedback voltage (Vfb). If Vfb
exceeds 2.8 V, D1 is blocked, and the 5 μA current
source starts to charge CB slowly up to VCC. In this
condition, Vfb continues increasing until it reaches 7.5 V,
then the switching operation is terminated as shown in
Figure 34. The delay for shutdown is the time required
to charge CB from 2.8 V to 7.5 V with 5 μA. In general, a
20~50 ms delay is typical for most applications. OLP is
implemented in auto restart mode.
Q
Gate
Driver
LEB
2
AOCP
GND
-
Figure 35.
VAOCP
AOCP Block
4.3 Over-Voltage Protection (OVP): If the secondary
side feedback circuit malfunctions or a solder defect
causes an open in the feedback path, the current
through the opto-coupler transistor becomes almost
zero. Then, Vfb climbs up in a similar manner to the over
load situation, forcing the preset maximum current to be
supplied to the SMPS until the over load protection
triggers. Because more energy than required is provided
to the output, the output voltage may exceed the rated
voltage before the overload protection triggers, resulting
in the breakdown of the devices in the secondary side.
In order to prevent this situation, an over voltage
protection (OVP) circuit is employed. In general, the
peak voltage of the sync signal is proportional to the
output voltage and the FSCQ series uses a sync signal
instead of directly monitoring the output voltage. If the
sync signal exceeds 12 V, an OVP is triggered resulting
in a shutdown of SMPS. In order to avoid undesired
triggering of OVP during normal operation, the peak
voltage of the sync signal should be designed to be
below 12 V. This protection is implemented in the auto
restart mode.
Overload Protection
4.4 Thermal Shutdown (TSD): The SenseFET and the
control IC are built in one package. This makes it easy
for the control IC to detect abnormal over temperature of
the SenseFET. When the temperature exceeds
approximately 150°C, the thermal shutdown triggers.
This protection is implemented in the latch mode.
2.8V
t12= CB*(7.5-2.8)/Idelay
Figure 34.
R
Rsense
7.5V
t1
Q
+
VFB
R
S
t2
t
Overload Protection
© 2006 Fairchild Semiconductor Corporation
FSQ-Series • Rev. 1.1.3
www.fairchildsemi.com
16
FSCQ-Series — Green Mode Fairchild Power Switch (FPS™)
Fault
occurs
Power
on
Vds
Figure 38 shows the burst mode operation waveforms.
When the picture ON signal is disabled, Q1 is turned off
and R3 and Dz are connected to the reference pin of
stby
KA431 through D1. Before Vo2 drops to Vo2 , the
voltage on the reference pin of KA431 is higher than
2.5 V, which increases the current through the opto
LED. This pulls down the feedback voltage (VFB) of
FSCQ series and forces FSCQ series to stop switching.
If the switching is disabled longer than 1.4 ms, FSCQ
series enters into burst operation and the operating
current is reduced from IOP to 0.25 mA (IOB). Since there
stby
is no switching, Vo2 decreases until it reaches Vo2 . As
stby
Vo2 reaches Vo2 , the current through the opto LED
decreases allowing the feedback voltage to rise. When
the feedback voltage reaches 0.4 V, FSCQ series
resumes switching with a predetermined peak drain
current of 0.9 A. After burst switching for 1.4 ms, FSCQ
series stops switching and checks the feedback voltage.
If the feedback voltage is below 0.4 V, FSCQ series
stops switching until the feedback voltage increases to
0.4 V. If the feedback voltage is above 0.4 V, FSCQ
series goes back to the normal operation. The output
voltage drop circuit can be implemented alternatively, as
shown in Figure 37. In the circuit, the FSCQ series goes
into burst mode, when picture off signal is applied to Q1.
Then, Vo2 is determined by the Zener diode breakdown
voltage. Assuming that the forward voltage drop of opto
LED is 1 V, the approximate value of Vo2 in standby
mode is given by:
6. Burst Operation: To minimize the power
consumption in the standby mode, the FSCQ series
employs burst operation. Once FSCQ series enters
burst mode, FSCQ series allows all output voltages and
effective switching frequency to be reduced. Figure 36
shows the typical feedback circuit for C-TV applications.
In normal operation, the picture on signal is applied and
the transistor Q1 is turned on, which decouples R3, DZ
and D1 from the feedback network. Therefore, only VO1
is regulated by the feedback circuit in normal operation
and determined by R1 and R2 as:
R R2
2.5 1
R2
NORM
VO1
(6)
In standby mode, the picture ON signal is disabled and
the transistor Q1 is turned off, which couples R3, DZ, and
D1 to the reference pin of KA431. Then, VO2 is
determined by the Zener diode breakdown voltage.
Assuming that the forward voltage drop of D1 is 0.7V,
VO2 in standby mode is approximately given by:
VO2
STBY
VZ 0.7 2.5
VO 2
STBY
(8)
VZ 1
VO2
(7)
Linear
Regulator
VO2
Linear
Regulator
VO1 (B+)
RD
RD
Micom
VO1 (B+)
Rbias
Dz
Rbias
R1
CF
RF
R3
CF
KA431
A
RF
R1
D1
Q1
C
Micom
C
Picture ON
KA431
R
R
R2
A
R2
Dz
Figure 36. Typical Feedback Circuit to Drop
Output Voltage in Standby Mode
Q1
Figure 37.
© 2006 Fairchild Semiconductor Corporation
FSQ-Series • Rev. 1.1.3
Picture OFF
Feedback Circuit to Drop Output
Voltage in Standby Mode
www.fairchildsemi.com
17
FSCQ-Series — Green Mode Fairchild Power Switch (FPS™)
5. Soft Start: The FSCQ series has an internal soft-start
circuit that increases PWM comparator’s inverting input
voltage together with the SenseFET current slowly after
it starts up. The typical soft start time is 20 ms. The
pulse width to the power switching device is
progressively increased to establish the correct working
conditions for transformers, inductors, and capacitors.
Increasing the pulse width to the power switching device
also helps prevent transformer saturation and reduces
the stress on the secondary diode during startup. For a
fast build up of the output voltage, an offset is
introduced in the soft-start reference current.
(b)
FSCQ-Series — Green Mode Fairchild Power Switch (FPS™)
(a)
(c)
Vo2norm
Vo2stby
VFB
0.4V
Iop
IOP
IOB
Vds
Picture
On
Picture
On
Picture Off
Burst Mode
0.4V
0.3V
VFB
0.4V
0.4V
Vds
1.4ms
Ids
1.4ms
0.9A
0.9A
(a) Mode Change to Burst Operation
Figure 38.
© 2006 Fairchild Semiconductor Corporation
FSQ-Series • Rev. 1.1.3
1.4ms
(b) Burst Operation
(c) Mode Change to Normal Operation
Burst Operation Waveforms
www.fairchildsemi.com
18
Application
Output Power
Input Voltage
Output Voltage (Max. Current)
12 V (0.5 A)
C-TV
18 V (0.3 A)
Universal Input
(90–270 Vac)
59 W
125 V (0.3 A)
24 V (0.4 A)
Features
High Efficiency (>83% at 90 Vac Input)
Wider Load Range through the Extended Quasi-Resonant Operation
Low Standby Mode Power Consumption (83% at 90 Vac Input)
Wider Load Range through the Extended Quasi-Resonant Operation
Low Standby Mode Power Consumption (83% at 90 Vac Input)
Wider Load Range through the Extended Quasi-Resonant Operation
Low Standby Mode Power Consumption (83% at 90 Vac Input)
Wider Load Range through the Extended Quasi-Resonant Operation
Low Standby Mode Power Consumption (83% at 90 Vac Input)
Wider Load Range through the Extended Quasi-Resonant Operation
Low Standby Mode Power Consumption (
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