FSQ0365, FSQ0265, FSQ0165, FSQ321
Green Mode Fairchild Power Switch (FPS™)
for Valley Switching Converter – Low EMI and High Efficiency
Features
Description
Optimized for Valley Switching Converter (VSC)
A Valley Switching Converter generally shows lower EMI
and higher power conversion efficiency than a
conventional hard-switched converter with a fixed
switching frequency. The FSQ-series is an integrated
Pulse-Width Modulation (PWM) controller and
SenseFET specifically designed for valley switching
operation with minimal external components. The PWM
controller includes an integrated fixed-frequency
oscillator, under-voltage lockout, Leading-Edge Blanking
(LEB), optimized gate driver, internal soft-start,
temperature-compensated precise current sources for
loop compensation, and self-protection circuitry.
Low EMI through Variable Frequency Control and
Inherent Frequency Modulation
High Efficiency through Minimum Voltage Switching
Narrow Frequency Variation Range Over Wide Load
and Input Voltage Variation
Advanced Burst-Mode Operation for Low Standby
Power Consumption
Pulse-by-Pulse Current Limit
Protection Functions: Overload Protection (OLP),
Over-Voltage Protection (OVP), Abnormal OverCurrent Protection (AOCP), Internal Thermal
Shutdown (TSD)
Under-Voltage Lockout (UVLO) with Hysteresis
Internal Startup Circuit
Compared with discrete MOSFET and PWM controller
solutions, the FSQ-series reduces total cost, component
count, size and weight; while simultaneously increasing
efficiency, productivity, and system reliability. This
device provides a basic platform for cost-effective
designs of valley switching fly-back converters.
Related Application Notes
AN-4137 - Design Guidelines for Offline Flyback
Converters Using Fairchild Power Switch (FPS™)
AN-4141 - Troubleshooting and Design Tips for
Fairchild Power Switch (FPS™) Flyback
Applications
Power Supplies for DVP Player, DVD Recorder,
AN-4147 - Design Guidelines for RCD Snubber of
Flyback Converters
Adapter
AN-4150 - Design Guidelines for Flyback
Converters Using FSQ-series Fairchild Power
Switch (FPS™)
AN-4134 - Design Guidelines for Off-line Forward
Converters Using Fairchild Power Switch (FPS™)
Internal High-Voltage SenseFET: 650V
Built-in Soft-Start: 15ms
Applications
Set-Top Box
Auxiliary Power Supply for PC, LCD TV, and PDP TV
© 2007 Fairchild Semiconductor Corporation
FSQ0365, FSQ0265, FSQ0165, FSQ321 • Rev. 1.0.6
www.fairchildsemi.com
FSQ0365/0265/0165/321 — Green Mode Fairchild Power Switch (FPS™) for Valley Switching Converter
August 2011
Maximum Output Table(1)
Operating Current RDS(ON)
230VAC ±15%(2)
85-265VAC
Part Number Package
Temperature Limit (Max.)
Open
Open
(3)
Adapter(3)
(4) Adapter
(4)
Frame
Frame
FSQ321
8-DIP
FSQ321L
8-LSOP
FSQ321LX
8-LSOP
(Tape &
Reel)
FSQ0165RN
8-DIP
FSQ0165RL
8-LSOP
8-LSOP
FSQ0165RLX (Tape &
Reel)
FSQ0265RN
8-DIP
FSQ0265RL
8-LSOP
FSQ0365RN
8-DIP
Replaces
Devices
-40 to +85°C
0.6A
19Ω
8W
12W
7W
10W
FSDL321
FSDM311
-40 to +85°C
0.9A
10Ω
10W
15W
9W
13W
FSDL0165RN
-40 to +85°C
1.2A
6Ω
14W
20W
11W
16W
FSDM0265RN
FSDM0265RNB
FSDM0365RN
-40 to +85°C 1.5A
4.5Ω
17.5W
25W
13W
19W
FSDM0365RNB
FSQ0365RL 8-LSOP
Notes:
1. The junction temperature can limit the maximum output power.
2. 230VAC or 100/115VAC with voltage doubler. The maximum power with CCM operation
3. Typical continuous power in a non-ventilated, enclosed adapter measured at 50C ambient temperature.
4. Maximum practical continuous power in an open-frame design at 50C ambient temperature.
© 2007 Fairchild Semiconductor Corporation
FSQ0365, FSQ0265, FSQ0165, FSQ321 • Rev. 1.0.6
www.fairchildsemi.com
2
FSQ0365/0265/0165/321 — Green Mode Fairchild Power Switch (FPS™) for Valley Switching Converter
Ordering Information
Vo
AC
IN
Vstr
Drain
PWM
Sync
Vfb
GND
Vcc
Figure 1.
Typical Flyback Application
Internal Block Diagram
Sync
4
Vstr
Vcc
5
2
Drain
6 7
8
+
OSC
0.7V/0.2V
+
+
Vref
VCC
Idelay
Vfb
3
0.35/0.55
VBurst
Vref
VCC Good
-
8V/12V
IFB
PWM
3R
R
S
SoftStart
LEB
200ns
Q
Gate
Driver
R Q
AOCP
VSD
Sync
Vovp
S
TSD
6V
2.5 s Time
Delay
1
Q
VOCP
(1.1V)
GND
R Q
6V
VCC Good
FSQ0365RN Rev.00
Figure 2.
© 2007 Fairchild Semiconductor Corporation
FSQ0365, FSQ0265, FSQ0165, FSQ321 • Rev. 1.0.6
Internal Block Diagram
www.fairchildsemi.com
3
FSQ0365/0265/0165/321 — Green Mode Fairchild Power Switch (FPS™) for Valley Switching Converter
Application Circuit
Figure 3.
Pin Configuration (Top View)
Pin Definitions
Pin#
Name
1
GND
SenseFET source terminal on primary side and internal control ground.
VCC
Positive supply voltage input. Although connected to an auxiliary transformer winding,
current is supplied from pin 5 (Vstr) via an internal switch during startup (see Figure 2).
It is not until VCC reaches the UVLO upper threshold (12V) that the internal startup switch
opens and device power is supplied via the auxiliary transformer winding.
Vfb
The feedback voltage pin is the non-inverting input to the PWM comparator. It has a
0.9mA current source connected internally while a capacitor and opto-coupler are typically
connected externally. There is a time delay while charging external capacitor Cfb from 3V
to 6V using an internal 5A current source. This delay prevents false triggering under
transient conditions, but still allows the protection mechanism to operate under true
overload conditions.
2
3
Description
4
Sync
This pin is internally connected to the sync-detect comparator for valley switching.
Typically the voltage of the auxiliary winding is used as Sync input voltage and external
resistors and capacitor are needed to make delay to match valley point. The threshold of
the internal sync comparator is 0.7V/0.2V.
5
Vstr
This pin is connected to the rectified AC line voltage source. At startup, the internal switch
supplies internal bias and charges an external storage capacitor placed between the Vcc
pin and ground. Once the VCC reaches 12V, the internal switch is opened.
6, 7, 8
Drain
The drain pins are designed to connect directly to the primary lead of the transformer and
are capable of switching a maximum of 650V. Minimizing the length of the trace
connecting these pins to the transformer decreases leakage inductance.
© 2007 Fairchild Semiconductor Corporation
FSQ0365, FSQ0265, FSQ0165, FSQ321 • Rev. 1.0.6
www.fairchildsemi.com
4
FSQ0365/0265/0165/321 — Green Mode Fairchild Power Switch (FPS™) for Valley Switching Converter
Pin Assignments
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
Min.
Max.
Unit
VSTR
Vstr Pin Voltage
500
V
VDS
Drain Pin Voltage
650
V
VCC
Supply Voltage
VFB
Feedback Voltage Range
Sync Pin Voltage
VSync
IDM
EAS
Drain Current Pulsed(6)
Single Pulsed Avalanche Energy(7)
20
V
-0.3
9.0
V
-0.3
9.0
V
FSQ0365
12.0
FSQ0265
8.0
FSQ0165
4.0
FSQ321
1.5
FSQ0365
230
FSQ0265
140
FSQ0165
50
FSQ321
10
PD
Total Power Dissipation
TJ
Recommended Operating Junction Temperature
TA
Operating Ambient Temperature
Storage Temperature
-55
TSTG
ESD
A
mJ
1.5
W
-40
Internally Limited
C
-40
+85
C
+150
C
Human Body Model; JESD22-A114
CLASS 1C
Machine Model; JESD22-A115
CLASS B
Notes:
5. Repetitive rating: Pulse width limited by maximum junction temperature.
6. L=51mH, starting TJ=25°C.
Thermal Impedance
Symbol
Parameter
Value
Unit
(7)
8-DIP
θJA
θJC
Junction-to-Ambient Thermal Resistance(8)
Junction-to-Case Thermal Resistance
80
(9)
20
θJT
Junction-to-Top Thermal Resistance(10)
Notes:
7. All items are tested with the standards JESD 51-2 and 51-10 (DIP).
8. Free-standing with no heat-sink, under natural convection.
9. Infinite cooling condition - refer to the SEMI G30-88.
10. Measured on the package top surface.
© 2007 Fairchild Semiconductor Corporation
FSQ0365, FSQ0265, FSQ0165, FSQ321 • Rev. 1.0.6
°C/W
35
www.fairchildsemi.com
5
FSQ0365/0265/0165/321 — Green Mode Fairchild Power Switch (FPS™) for Valley Switching Converter
Absolute Maximum Ratings
T A=25C unless otherwise specified.
Symbol
Parameter
Condition
Min.
Typ.
Max.
Unit
SenseFET Section
BVDSS
Drain-Source Breakdown Voltage
VCC=0V, ID=100µA
IDSS
Zero-Gate-Voltage Drain Current
VDS=650V
650
100
3.5
4.5
5.0
6.0
8.0
10.0
FSQ321
14.0
19.0
FSQ0365
315
FSQ0365
RDS(ON)
CISS
COSS
Drain-Source OnState Resistance(11)
Input Capacitance
Output Capacitance
FSQ0265
FSQ0165
FSQ0265
FSQ0165
TJ=25C, ID=0.5A
550
VGS=0V, VDS=25V, f=1MHz
FSQ321
162
FSQ0365
47
FSQ0265
FSQ0165
38
VGS=0V, VDS=25V, f=1MHz
Reverse Transfer
Capacitance
18
9.0
FSQ0265
17.0
VGS=0V, VDS=25V, f=1MHz
tr
td(off)
tf
Turn-On Delay
Rise Time
Turn-Off Delay
Fall Time
3.8
FSQ0365
11.2
FSQ0265
20.0
FSQ0165
VDD=350V, ID=25mA
9.5
FSQ0365
34
FSQ0165
15
VDD=350V, ID=25mA
19
FSQ0365
28.2
FSQ0165
55.0
VDD=350V, ID=25mA
33.0
FSQ0365
32
FSQ0165
ns
30.0
FSQ321
FSQ0265
ns
4
FSQ321
FSQ0265
ns
12.0
FSQ321
FSQ0265
pF
10.0
FSQ321
td(on)
pF
25
FSQ0365
FSQ0165
µA
pF
250
FSQ321
CRSS
V
25
VDD=350V, ID=25mA
ns
10
FSQ321
42
Burst-Mode Section
VBURH
VBURL
Burst-Mode Voltage
TJ=25°C, tPD=200ns(12)
VBUR(HYS)
0.45
0.55
0.65
0.25
0.35
0.45
200
V
V
mV
Continued on the following page…
© 2007 Fairchild Semiconductor Corporation
FSQ0365, FSQ0265, FSQ0165, FSQ321 • Rev. 1.0.6
www.fairchildsemi.com
6
FSQ0365/0265/0165/321 — Green Mode Fairchild Power Switch (FPS™) for Valley Switching Converter
Electrical Characteristics
T A=25C unless otherwise specified.
Symbol
Parameter
Conditions
Min.
Typ.
Max.
Unit
All but
T =25°C
FSQ321 J
10.5
12.0
13.5
µs
Control Section
tON.MAX1
Maximum On Time1
tON.MAX2
Maximum On Time2
FSQ321 TJ=25°C
6.35
7.06
7.77
µs
tB1
Blanking Time1
All but
FSQ321
13.2
15.0
16.8
µs
tB2
Blanking Time2
FSQ321
7.5
tW
Detection Time Window
(14)
8.2
µs
TJ=25°C, Vsync=0V
3.0
µs
±5
±10
%
700
900
1100
µA
0
%
11
12
13
V
7
8
9
V
fS
Switching Frequency Variation
-25C < TJ < 85C
IFB
Feedback Source Current
VFB=0V
Minimum Duty Cycle
VFB=0V
DMIN
VSTART
VSTOP
UVLO Threshold Voltage
After Turn-on
tS/S1
Internal Soft-Start Time 1
All but
With Free-Running
FSQ321 Frequency
tS/S2
Internal Soft-Start Time 2
FSQ321
15
ms
With Free-Running
Frequency
10
ms
Protection Section
ILIM
VSD
IDELAY
FSQ0365
TJ=25°C, di/dt=240mA/µs
1.32
1.50
1.68
FSQ0265
TJ=25°C, di/dt=200mA/µs
1.06
1.20
1.34
FSQ0165
TJ=25°C, di/dt=175mA/µs
0.8
0.9
1.0
FSQ321
TJ=25°C, di/dt=125mA/µs
0.53
0.60
0.67
Shutdown Feedback Voltage
VCC=15V
5.5
6.0
6.5
V
Shutdown Delay Current
VFB=5V
4.0
5.0
6.0
µA
Peak Current Limit
tLEB
Leading-Edge Blanking Time(13)
VOVP
Over-Voltage Protection
tOVP
Over-Voltage Protection Blanking
Time
TSD
Thermal Shutdown Temperature(13)
200
VCC=15V, VFB=2V
A
ns
5.5
6.0
6.5
V
2
3
4
µs
125
140
155
°C
Sync Section
VSH
VSL
tSync
Sync Threshold Voltage
0.55
0.70
0.85
V
0.14
0.20
0.26
V
Sync Delay Time(13,14)
300
ns
Total Device Section
IOP
ISTART
ICH
Operating Supply Current
(Control Part Only)
VCC=15V
Start Current
Startup Charging Current
1
3
5
mA
VCC=VSTART - 0.1V
(Before VCC Reaches VSTART)
270
360
450
µA
VCC=0V, VSTR=Minimum 40V
0.65
0.85
1.00
mA
VSTR
Minimum VSTR Supply Voltage
Notes:
11. Pulse test: Pulse-Width=300s, duty=2%.
12. Propagation delay in the control IC.
13. Though guaranteed, it is not 100% tested in production.
14. Includes gate turn-on time.
© 2007 Fairchild Semiconductor Corporation
FSQ0365, FSQ0265, FSQ0165, FSQ321 • Rev. 1.0.6
26
V
www.fairchildsemi.com
7
FSQ0365/0265/0165/321 — Green Mode Fairchild Power Switch (FPS™) for Valley Switching Converter
Electrical Characteristics (Continued)
Function
FSDM0x65RNB
FSQ-Series
Operation Method
Constant
Frequency PWM
Valley Switching
Operation
EMI Reduction
Frequency
Modulation
Valley Switching &
Inherent Frequency
Modulation
Advantages of FSQ-Series
Improved efficiency by valley switching
Reduced EMI noise
Reduce EMI noise in two ways
Improved standby power by valley switching also in
Burst-Mode
Operation
Fixed Burst Peak
Protection
© 2007 Fairchild Semiconductor Corporation
FSQ0365, FSQ0265, FSQ0165, FSQ321 • Rev. 1.0.6
burst-mode
Advanced BurstMode
Because the current peak during burst operation is
AOCP
Improved reliability through precise abnormal over-
dependent on VFB, it is easier to solve audible
noise
current protection
www.fairchildsemi.com
8
FSQ0365/0265/0165/321 — Green Mode Fairchild Power Switch (FPS™) for Valley Switching Converter
Comparison Between FSDM0x65RNB and FSQ-Series
1.2
1.2
1.0
1.0
Normalized
Normalized
Characteristic graphs are normalized at TA=25°C.
0.8
0.6
0.4
0.2
0.0
-25
0.8
0.6
0.4
0.2
0
25
50
75
100
0.0
-25
125
0
Temperature [°C]
Operating Supply Current (IOP) vs. TA
Figure 5.
1.2
1.2
1.0
1.0
Normalized
Normalized
Figure 4.
0.8
0.6
0.4
0.2
0.0
-25
125
0.4
0.2
0
25
50
75
100
0.0
-25
125
0
25
50
75
100
125
Temperature [°C]
UVLO Stop Threshold Voltage (VSTOP)
vs. TA
Figure 7.
1.0
1.0
Normalized
Normalized
100
0.6
1.2
0.8
0.6
0.4
0.2
Startup Charging Current (ICH) vs. TA
0.8
0.6
0.4
0.2
0
25
50
75
100
0.0
-25
125
Temperature [°C]
Figure 8.
75
0.8
1.2
0.0
-25
50
UVLO Start Threshold Voltage (VSTART)
vs. TA
Temperature [°C]
Figure 6.
25
Temperature [°C]
25
50
75
100
125
Temperature [°C]
Initial Switching Frequency (fS) vs. TA
© 2007 Fairchild Semiconductor Corporation
FSQ0365, FSQ0265, FSQ0165, FSQ321 • Rev. 1.0.6
0
Figure 9.
Maximum On Time (tON.MAX) vs. TA
www.fairchildsemi.com
9
FSQ0365/0265/0165/321 — Green Mode Fairchild Power Switch (FPS™) for Valley Switching Converter
Typical Performance Characteristics
1.2
1.2
1.0
1.0
Normalized
Normalized
Characteristic graphs are normalized at TA=25°C.
0.8
0.6
0.4
0.2
0.0
-25
0.8
0.6
0.4
0.2
0
25
50
75
100
0.0
-25
125
0
Temperature [°C]
1.2
1.2
1.0
1.0
0.8
0.6
0.4
0.2
100
125
0.6
0.4
0.2
0
25
50
75
100
0.0
-25
125
0
25
50
75
100
125
Temperature [°C]
Figure 12. Shutdown Delay Current (IDELAY) vs. TA
Figure 13. Burst Mode High Threshold Voltage (Vburh)
vs. TA
1.2
1.2
1.0
1.0
Normalized
Normalized
75
0.8
Temperature [°C]
0.8
0.6
0.4
0.2
0.0
-25
50
Figure 11. Feedback Source Current (IFB) vs. TA
Normalized
Normalized
Figure 10. Blanking Time (tB) vs. TA
0.0
-25
25
Temperature [°C]
0.8
0.6
0.4
0.2
0
25
50
75
100
0.0
-25
125
Temperature [°C]
25
50
75
100
125
Temperature [°C]
Figure 14. Burst Mode Low Threshold Voltage (Vburl)
vs. TA
© 2007 Fairchild Semiconductor Corporation
FSQ0365, FSQ0265, FSQ0165, FSQ321 • Rev. 1.0.6
0
Figure 15. Peak Current Limit (ILIM) vs. TA
www.fairchildsemi.com
10
FSQ0365/0265/0165/321 — Green Mode Fairchild Power Switch (FPS™) for Valley Switching Converter
Typical Performance Characteristics (Continued)
1.2
1.2
1.0
1.0
Normalized
Normalized
Characteristic graphs are normalized at TA=25°C.
0.8
0.6
0.4
0.2
0.0
-25
0.8
0.6
0.4
0.2
0
25
50
75
100
0.0
-25
125
0
Temperature [°C]
50
75
100
125
Figure 17. Sync Low Threshold Voltage (VSL) vs. TA
1.2
1.2
1.0
1.0
Normalized
Normalized
Figure 16. Sync High Threshold (VSH) vs. TA
0.8
0.6
0.4
0.2
0.0
-25
25
Temperature [°C]
0.8
0.6
0.4
0.2
0
25
50
75
100
0.0
-25
125
Temperature [°C]
Figure 18. Shutdown Feedback Voltage (VSD) vs. TA
© 2007 Fairchild Semiconductor Corporation
FSQ0365, FSQ0265, FSQ0165, FSQ321 • Rev. 1.0.6
0
25
50
75
100
125
Temperature [°C]
Figure 19. Over-Voltage Protection (VOP) vs. TA
www.fairchildsemi.com
11
FSQ0365/0265/0165/321 — Green Mode Fairchild Power Switch (FPS™) for Valley Switching Converter
Typical Performance Characteristics (Continued)
1. Startup: At startup, an internal high-voltage current
source supplies the internal bias and charges the
external capacitor (Ca) connected to the VCC pin, as
illustrated in Figure 20. When VCC reaches 12V, the
FPS™ begins switching and the internal high-voltage
current source is disabled. The FPS continues its
normal switching operation and the power is supplied
from the auxiliary transformer winding unless VCC goes
below the stop voltage of 8V.
Vref
VCC
Idelay
VFB
VO
IFB
3
FOD817A
SenseFET
OSC
D1
CB
D2
3R
+
VFB*
KA431
Gate
driver
R
-
VDC
OLP
VSD
Rsense
FSQ0365RN Rev. 00
Ca
Figure 21. Pulse-Width-Modulation (PWM) Circuit
VCC
2
5
Vstr
ICH
Vref
8V/12V
VCC good
FSQ0365RN Rev.00
Internal
Bias
3. Synchronization: The FSQ-series employs a valley
switching technique to minimize the switching noise and
loss. The basic waveforms of the valley switching
converter are shown in Figure 22. 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 22. The minimum drain
voltage is indirectly detected by monitoring the VCC
winding voltage, as shown in Figure 22.
Vds
Figure 20. Startup Circuit
2. Feedback Control: FPS employs Current Mode
control, as shown in Figure 21. An opto-coupler (such as
FOD817A) and shunt regulator (such as KA431) are
often used to implement the feedback network.
Comparing the feedback voltage with the voltage across
the RSENSE resistor makes it possible to control the
switching duty cycle. When the reference pin voltage of
the shunt regulator exceeds the internal reference
voltage of 2.5V, the opto-coupler LED current increases,
pulling down the feedback voltage and reducing the duty
cycle. This event typically occurs when input voltage is
increased or output load is decreased.
2.1 Pulse-by-Pulse Current Limit: Because Current
Mode control is employed, the peak current through the
SenseFET is limited by the inverting input of PWM
comparator (VFB*), as shown in Figure 21. Assuming
that the 0.9mA current source flows only through the
internal resistor (3R + R = 2.8kΩ), the cathode voltage
of diode D2 is about 2.5V. Since D1 is blocked when the
feedback voltage (VFB) exceeds 2.5V, the maximum
voltage of the cathode of D2 is clamped at this voltage,
clamping VFB*. Therefore, the peak value of the current
through the SenseFET is limited.
2.2 Leading-Edge Blanking (LEB): At the instant the
internal SenseFET is turned on, a high-current spike
usually occurs through the SenseFET, caused by
primary-side capacitance and secondary-side rectifier
reverse recovery. Excessive voltage across the Rsense
resistor would lead to incorrect feedback operation in the
Current Mode PWM control. To counter this effect, the
FPS employs a leading-edge blanking (LEB) circuit. This
circuit inhibits the PWM comparator for a short time
(tLEB) after the SenseFET is turned on.
© 2007 Fairchild Semiconductor Corporation
FSQ0365, FSQ0265, FSQ0165, FSQ321 • Rev. 1.0.6
VRO
VRO
VDC
tF
Vsync
Vovp (6V)
0.7V
0.2V
300ns Delay
MOSFET Gate
ON
ON
FSQ0365RN Rev.00
Figure 22. Valley Resonant Switching Waveforms
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 AutoRestart 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, the FSQ-series resumes normal operation. If the
fault condition is not removed, the SenseFET remains
off and VCC drops to stop voltage again. In this manner,
www.fairchildsemi.com
12
FSQ0365/0265/0165/321 — Green Mode Fairchild Power Switch (FPS™) for Valley Switching Converter
Functional Description
VDS
Power
on
Fault
occurs
VFB
FSQ0365RN Rev.00
Overload protection
6.0V
2.8V
Fault
removed
t12= CFB*(6.0-2.8)/Idelay
t1
t2
t
Figure 24. Overload Protection
8V
t
FSQ0365RN Rev. 00
Normal
operation
Fault
situation
Normal
operation
Figure 23. Auto-Restart Protection Waveforms
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 overload protection circuit can be
triggered during load transition. To avoid this undesired
operation, the overload protection circuit is designed to
trigger only after a specified time to determine whether it
is a transient situation or a true 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 2.8V, D1 is blocked and the 5µA current source
starts to charge CB slowly up to VCC. In this condition,
VFB continues increasing until it reaches 6V, when the
switching operation is terminated, as shown in Figure
24. The delay for shutdown is the time required to
charge CB from 2.8V to 6V with 5µA. A 20 ~ 50ms delay
is typical for most applications.
© 2007 Fairchild Semiconductor Corporation
FSQ0365, FSQ0265, FSQ0165, FSQ321 • Rev. 1.0.6
3R
OSC
PWM
LEB
200ns
S
Q
R
Q
Gate
driver
R
Rsense
1
GND
AOCP
-
12V
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 FSQ-series has Overload Protection
(OLP), it is not enough to protect the FSQ-series in that
abnormal case, since severe current stress is imposed
on the SenseFET until OLP triggers. The FSQ-series
has an internal Abnormal Over-Current Protection
(AOCP) circuit as shown in Figure 25. 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 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 the SMPS.
+
VCC
FSQ0365RN Rev.00
VOCP
Figure 25. Abnormal Over-Current Protection
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13
FSQ0365/0265/0165/321 — Green Mode Fairchild Power Switch (FPS™) for Valley Switching Converter
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, the reliability is improved without
increasing cost.
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 the abnormal over
temperature of the SenseFET. If the temperature
exceeds ~150°C, the thermal shutdown triggers.
5. Soft-Start: An internal soft-start circuit increases
PWM comparator inverting input voltage with the
SenseFET current slowly after it starts up. The typical
soft-start time is 15ms. The pulsewidth to the power
switching device is progressively increased to establish
the correct working conditions for transformers,
inductors, and capacitors. The voltage on the output
capacitors is progressively increased with the intention
of smoothly establishing the required output voltage.
This helps prevent transformer saturation and reduces
stress on the secondary diode during startup.
6. Burst Operation: To minimize power dissipation in
Standby Mode, the FPS enters Burst-Mode operation.
As the load decreases, the feedback voltage decreases.
As shown in Figure 26, the device automatically enters
Burst Mode when the feedback voltage drops below
VBURL (350mV). At this point, switching stops and the
output voltages start to drop at a rate dependent on
standby current load. This causes the feedback voltage
to rise. Once it passes VBURH (550mV), switching
resumes. The feedback voltage then falls and the
process repeats. Burst Mode alternately enables and
disables switching of the power SenseFET, reducing
switching loss in Standby Mode.
© 2007 Fairchild Semiconductor Corporation
FSQ0365, FSQ0265, FSQ0165, FSQ321 • Rev. 1.0.6
VO
VOset
VFB
0.55V
0.35V
IDS
VDS
time
FSQ0365RN Rev.00
t1
Switching
disabled
t2 t3
Switching
disabled
t4
Figure 26. Waveforms of Burst Operation
7. Switching Frequency Limit: To minimize switching
loss and Electromagnetic Interference (EMI), the
MOSFET turns on when the drain voltage reaches its
minimum value in valley switching operation. However,
this causes switching frequency to increases at light
load conditions. As the load decreases, the peak drain
current diminishes and the switching frequency
increases. This results in severe switching losses at
light-load condition, as well as intermittent switching and
audible noise. Because of these problems, the valley
switching converter topology has limitations in a wide
range of applications.
To overcome this problem, FSQ-series employs a
frequency-limit function, as shown in Figure 27 and
Figure 28. Once the SenseFET is turned on, the next
turn-on is prohibited during the blanking time (tB). After
the blanking time, the controller finds the valley within
the detection time window (tW ) and turns on the
MOSFET, as shown in Figure 27 and Figure 28 (cases
A, B, and C). If no valley is found during tW , the internal
SenseFET is forced to turn on at the end of tW (case D).
Therefore, FSQ devices have a minimum switching
frequency of 55kHz and a maximum switching frequency
of 67kHz, as shown in Figure 28.
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14
FSQ0365/0265/0165/321 — Green Mode Fairchild Power Switch (FPS™) for Valley Switching Converter
4.3 Over-Voltage Protection (OVP): If the secondaryside feedback circuit malfunctions or a solder defect
causes an opening in the feedback path, the current
through the opto-coupler transistor becomes almost
zero. Then VFB climbs up in a similar manner to the
overload situation, forcing the preset maximum current
to be supplied to the SMPS until the overload 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.
To prevent this situation, an OVP circuit is employed. In
general, the peak voltage of the sync signal is
proportional to the output voltage and the FSQ-series
uses a sync signal instead of directly monitoring the
output voltage. If the sync signal exceeds 6V, an OVP is
triggered, shutting down the SMPS. To avoid undesired
triggering of OVP during normal operation, the peak
voltage of the sync signal should be designed below 6V.
When the resonant period is 2s
67kHz
IDS
IDS
A
A
59kHz
55kHz
B
C
Constant
frequency
D
tB=15s
Burst
mode
ts
IDS
IDS
B
PO
FSQ0365RN Rev. 00
tB=15s
Figure 28. Switching Frequency Range
ts
IDS
IDS
C
tB=15s
ts
IDS
IDS
tB=15s
D
tW=3s
tsmax=18s
FSQ0365RN Rev. 00
Figure 27. Valley Switching with Limited Frequency
© 2007 Fairchild Semiconductor Corporation
FSQ0365, FSQ0265, FSQ0165, FSQ321 • Rev. 1.0.6
www.fairchildsemi.com
15
FSQ0365/0265/0165/321 — Green Mode Fairchild Power Switch (FPS™) for Valley Switching Converter
tsmax=18s
Application
Input Voltage
Range
FPS Device
DVD Player
Power Supply
FSQ0365RN
Rated Output Power
Output Voltage
(Maximum Current)
19W
5.1V (1.0A)
3.4V (1.0A)
12V (0.4A)
16V (0.3A)
85-265VAC
Features
High efficiency ( >77% at universal input)
Low standby mode power consumption (
