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FAN7621
PFM Controller for Half-Bridge Resonant Converters
Features
Description
The FAN7621 is a pulse frequency modulation controller
for high-efficiency half-bridge resonant converters.
Offering everything necessary to build a reliable and
robust resonant converter, the FAN7621 simplifies
designs and improves productivity, while improving
performance. The FAN7621 includes a high-side gatedrive circuit, an accurate current controlled oscillator,
frequency limit circuit, soft-start, and built-in protection
functions. The high-side gate-drive circuit has a
common-mode noise cancellation capability, which
guarantees stable operation with excellent noise
immunity. Using the zero-voltage-switching (ZVS)
technique dramatically reduces the switching losses and
efficiency is significantly improved. The ZVS also
reduces the switching noise noticeably, which allows a
small-sized Electromagnetic Interference (EMI) filter.
Variable Frequency Control with 50% Duty Cycle
for Half-bridge Resonant Converter Topology
High Efficiency through Zero Voltage Switching (ZVS)
Fixed Dead Time (350ns)
Up to 300kHz Operating Frequency
Pulse Skipping for Frequency Limit (Programmable)
at Light-Load Condition
Remote On/Off Control Using CON Pin
Protection Functions: Over-Voltage Protection
(OVP), Overload Protection (OLP), Over-Current
Protection (OCP), Abnormal Over-Current Protection
(AOCP), Internal Thermal Shutdown (TSD)
Applications
PDP and LCD TVs
Desktop PCs and Servers
Adapters
Telecom Power Supplies
Video Game Consoles
The FAN7621 can be applied to various resonant
converter topologies; such as series resonant, parallel
resonant, and LLC resonant converters.
Related Resources
AN4151 — Half-bridge LLC Resonant Converter Design
TM
using FSFR-series Fairchild Power Switch (FPS )
Ordering Information
Part Number
Operating Junction
Temperature
FAN7621N
FAN7621SJ
-40°C ~ 130°C
FAN7621SJX
© 2009 Fairchild Semiconductor Corporation
FAN7621 • Rev. 1.0.3
Package
Packaging Method
16-Lead, Dual Inline Package (DIP)
Tube
16-Lead, Small-Outline Package (SOP)
Tube
16-Lead, Small-Outline Package (SOP)
Tape & Reel
www.fairchildsemi.com
FAN7621 — PFM Controller for Half-Bridge Resonant Converters
July 2010
D1
Cr
L lk
VCC
Np
Lm
LVcc
CON
CDL
VIN
FAN7621
HV CC
RT
VO
Ns
Ns
HO
CF R F
D2
CTR
KA431
LO
CS
SG
PG
Rsense
Figure 1. Typical Application Circuit (LLC Resonant Half-Bridge Converter)
Block Diagram
LVCC
12
I CTC
+
2ICTC
3V
-
1V
+
S
Q
R
-Q
11.3 / 14.5V
LVCC good
VREF
-
8.7 / 9.2V
HVCC good
Internal
Bias
+
I CTC
-
+
VREF
1
F/F
-
2V
Time
Delay
+
-
RT
High-Side
Gate Drive
Level-Shift
8
Counter (1/4)
LVCC
6
Time
Delay
0.4 / 0.6 V
HO
2
CTR
+
OLP
-
LVCC
+
23 V
-
Low-Side
Gate Drive
Balancing
Delay
14
LO
350ns
+
5V
3
350ns
I OLP
CON
HVCC
LVCC good
OVP
S
Q
R
-Q
Auto-restart
Protection
Shutdown without delay
-1
+
Q
S
-Q
R
50ns Delay
0.9 V
-
V AOCP
TSD
Latch
Protection
LVCC < 5V
Delay
1.5µs
-
16
PG
10
SG
V OCP
0.58 V
+
9
CS
Figure 2. Internal Block Diagram
© 2009 Fairchild Semiconductor Corporation
FAN7621 • Rev. 1.0.3
www.fairchildsemi.com
2
FAN7621 — PFM Controller for Half-Bridge Resonant Converters
Application Circuit Diagram
FAN7621 — PFM Controller for Half-Bridge Resonant Converters
Pin Configuration
(1) HVCC
PG (16)
(2) CTR
NC (15)
(3) HO
LO (14)
(4) NC
NC (13)
FAN7621
(5) NC
LVCC (12)
(6) CON
NC (11)
(7) NC
SG (10)
(8) RT
CS (9)
Figure 3. Package Diagram
Pin Definitions
Pin #
Name
Description
1
HVCC
This is the supply voltage of the high-side gate-drive circuit IC.
2
CTR
This is the drain of the low-side MOSFET. Typically, a transformer is connected to this pin.
3
HO
This is the high-side gate driving signal.
4
NC
No connection.
5
NC
No connection.
This pin is for a protection and enabling/disabling the controller. When the voltage of this pin
is above 0.6V, the IC operation is enabled. When the voltage of this pin drops below 0.4V,
gate drive signals for both MOSFETs are disabled. When the voltage of this pin increases
above 5V, protection is triggered.
6
CON
7
NC
No connection.
8
RT
This pin programs the switching frequency. Typically, an opto-coupler is connected to
control the switching frequency for the output voltage regulation.
9
CS
This pin senses the current flowing through the low-side MOSFET. Typically, negative
voltage is applied on this pin.
10
SG
This pin is the control ground.
11
NC
No connection.
12
LVCC
13
NC
No connection.
14
LO
This is the low-side gate driving signal.
15
NC
No connection.
16
PG
This pin is the power ground. This pin is connected to the source of the low-side MOSFET.
This pin is the supply voltage of the control IC.
© 2009 Fairchild Semiconductor Corporation
FAN7621 • Rev. 1.0.3
www.fairchildsemi.com
3
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
VHO
High-Side Gate Driving Voltage
VCTR-0.3
HVCC
VLO
Low-Side Gate Driving Voltage
-0.3
LVCC
Low-Side Supply Voltage
-0.3
25.0
V
-0.3
25.0
V
-0.3
600.0
V
LVCC
HVCC to VCTR High-Side VCC Pin to Center Voltage
VCTR
Center Voltage
V
VCON
Control Pin Input Voltage
-0.3
LVCC
V
VCS
Current Sense (CS) Pin Input Voltage
-5.0
1.0
V
VRT
RT Pin Input Voltage
-0.3
5.0
V
dVCTR/dt
PD
TJ
TSTG
Allowable Center Voltage Slew Rate
Total Power Dissipation
50
V/ns
16-DIP
1.56
W
16-SOP
1.13
W
Maximum Junction Temperature
(1)
+150
Recommended Operating Junction Temperature
(1)
Storage Temperature Range
-40
+130
-55
+150
°C
°C
Note:
1. The maximum value of the recommended operating junction temperature is limited by thermal shutdown.
Thermal Impedance
Symbol
θJA
Parameter
Junction-to-Ambient Thermal Impedance
© 2009 Fairchild Semiconductor Corporation
FAN7621 • Rev. 1.0.3
Value
16-DIP
80
16-SOP
110
Unit
ºC/W
www.fairchildsemi.com
4
FAN7621 — PFM Controller for Half-Bridge Resonant Converters
Absolute Maximum Ratings
TA=25°C and LVCC=17V unless otherwise specified.
Symbol
Parameter
Test Conditions
Min.
Typ.
Max.
Unit
50
μA
Supply Section
ILK
Offset Supply Leakage Current
HVCC=VCTR
IQHVCC
Quiescent HVCC Supply Current
(HVCCUV+) - 0.1V
50
120
μA
IQLVCC
Quiescent LVCC Supply Current
(LVCCUV+) - 0.1V
100
200
μA
IOHVCC
Operating HVCC Supply Current
(RMS Value)
fOSC=100kHz, VCON > 0.6V,
CLoad=1nF
5
8
mA
No Switching, VCON < 0.4V
100
200
μA
fOSC=100kHz, VCON > 0.6V,
CLoad=1nF
6
9
mA
No Switching, VCON < 0.4V
2
4
mA
IOLVCC
Operating LVCC Supply Current
(RMS Value)
UVLO Section
LVCCUV+
LVCC Supply Under-Voltage Positive Going Threshold (LVCC Start)
13.0
14.5
16.0
V
LVCCUV-
LVCC Supply Under-Voltage Negative Going Threshold (LVCC Stop)
10.2
11.3
12.4
V
LVCCUVH
LVCC Supply Under-Voltage Hysteresis
HVCCUV+
HVCC Supply Under-Voltage Positive Going Threshold (HVCC Start)
8.2
9.2
10.2
V
HVCCUV-
HVCC Supply Under-Voltage Negative Going Threshold (HVCC Stop)
7.8
8.7
9.6
V
HVCCUVH
HVCC Supply Under-Voltage Hysteresis
3.2
V
0.5
V
Oscillator & Feedback Section
VCONDIS
Control Pin Disable Threshold Voltage
0.36
0.40
0.44
V
VCONEN
Control Pin Enable Threshold Voltage
0.54
0.60
0.66
V
VRT
V-I Converter Threshold Voltage
1.5
2.0
2.5
V
fOSC
Output Oscillation Frequency
94
100
106
kHz
DC
Output Duty Cycle
48
50
52
%
fSS
Internal Soft-Start Initial Frequency
tSS
Internal Soft-Start Time
RT=5.2kΩ
fSS=fOSC+40kHz, RT=5.2kΩ
140
2
3
kHz
4
ms
Output Section
Isource
Isink
Peak Sourcing Current
HVCC=17V
250
360
mA
Peak Sinking Current
HVCC=17V
460
600
mA
65
ns
35
ns
tr
Rising Time
tf
Falling Time
VHOH
High Level of High-Side Gate Driving
Signal (VHVCC-VHO)
VHOL
Low Level of High-Side Gate Driving
Signal
VLOH
High Level of High-Side Gate Driving
Signal (VLVCC-VLO)
VLOL
Low Level of High-Side Gate Driving
Signal
© 2009 Fairchild Semiconductor Corporation
FAN7621 • Rev. 1.0.3
CLoad=1nF, HVCC=17V
1.0
V
0.6
V
1.0
V
0.6
V
IO=20mA
www.fairchildsemi.com
5
FAN7621 — PFM Controller for Half-Bridge Resonant Converters
Electrical Characteristics
TA=25°C and LVCC=17V unless otherwise specified.
Symbol
Parameter
Test Conditions
Min.
Typ.
Max.
Unit
Protection Section
IOLP
OLP Delay Current
VCON=4V
3.8
5.0
6.2
μA
VOLP
OLP Protection Voltage
VCON > 3.5V
4.5
5.0
5.5
V
VOVP
LVCC Over-Voltage Protection
LVCC > 21V
21
23
25
V
VAOCP
AOCP Threshold Voltage
-1.0
-0.9
-0.8
V
tBAO
AOCP Blanking Time
VOCP
OCP Threshold Voltage
50
(2)
tBO
OCP Blanking Time
tDA
Delay Time (Low-Side) Detecting from
(2)
VAOCP to Switch Off
TSD
Thermal Shutdown Temperature
ISU
Protection Latch Sustain LVCC Supply
Current
VPRSET
(2)
-0.64
-0.58
-0.52
V
1.0
1.5
2.0
μs
250
400
ns
130
150
°C
100
150
μA
110
LVCC=7.5V
Protection Latch Reset LVCC Supply
Voltage
ns
5
V
Dead-Time Control Section
DT
Dead Time
350
ns
Note:
2. These parameters, although guaranteed, are not tested in production.
© 2009 Fairchild Semiconductor Corporation
FAN7621 • Rev. 1.0.3
www.fairchildsemi.com
6
FAN7621 — PFM Controller for Half-Bridge Resonant Converters
Electrical Characteristics (Continued)
1.1
1.1
1.05
1.05
Normalized at 25OC
Normalized at 25OC
These characteristic graphs are normalized at TA=25ºC.
1
0.95
1
0.95
0.9
0.9
-50
-25
0
25
50
75
-50
100
-25
0
O
Temp ( C)
Temp
Figure 4. Low-Side MOSFET Duty Cycle
vs. Temperature
50
75
100
(OC)
Figure 5. Switching Frequency vs. Temperature
1.1
1.1
1.05
1.05
Normalized at 25OC
Normalized at 25OC
25
1
0.95
0.9
1
0.95
0.9
-50
-25
0
25
50
75
100
-50
-25
0
25
50
75
100
Temp (OC)
Figure 6. High-Side VCC (HVCC) Start vs. Temperature
Figure 7. High-Side VCC (HVCC) Stop vs. Temperature
1.1
1.1
1.05
1.05
Normalized at 25OC
Normalized at 25OC
Temp (OC)
1
0.95
1
0.95
0.9
0.9
-50
-25
0
25
Temp
50
75
100
-50
Figure 8. Low-Side VCC (LVCC) Start vs. Temperature
© 2009 Fairchild Semiconductor Corporation
FAN7621 • Rev. 1.0.3
-25
0
25
50
75
100
Temp (OC)
(OC)
Figure 9. Low-Side VCC (LVCC) Stop vs. Temperature
www.fairchildsemi.com
7
FAN7621 — PFM Controller for Half-Bridge Resonant Converters
Typical Performance Characteristics
1.1
1.1
1.05
1.05
Normalized at 25OC
Normalized at 25OC
These characteristic graphs are normalized at TA=25ºC.
1
0.95
0.95
0.9
0.9
-50
-25
0
25
50
75
-50
100
-25
0
50
75
100
Temp (OC)
Figure 10. OLP Delay Current vs. Temperature
Figure 11. OLP Protection Voltage vs. Temperature
1.1
1.1
1.05
1.05
1
0.95
1
0.95
0.9
0.9
-50
-25
0
25
50
75
-50
100
-25
0
Temp (OC)
25
Temp
Figure 12. LVCC OVP Voltage vs. Temperature
50
75
100
(OC)
Figure 13. RT Voltage vs. Temperature
1.1
1.1
1.05
1.05
Normalized at 25OC
Normalized at 25OC
25
Temp (OC)
Normalized at 25OC
Normalized at 25OC
1
1
0.95
0.9
1
0.95
0.9
-50
-25
0
25
50
75
-50
100
-25
0
25
50
75
100
Temp (OC)
Temp (OC)
Figure 14. CON Pin Enable Voltage vs. Temperature
Figure 15. OCP Voltage vs. Temperature
© 2009 Fairchild Semiconductor Corporation
FAN7621 • Rev. 1.0.3
www.fairchildsemi.com
8
FAN7621 — PFM Controller for Half-Bridge Resonant Converters
Typical Performance Characteristics (Continued)
Gain
1. Basic Operation
FAN7621 is designed to drive high-side and low-side
MOSFETs complementarily with 50% duty cycle. A fixed
dead time of 350ns is introduced between consecutive
transitions, as shown in Figure 16.
1.8
f min
f normal
f
max
f ISS
1.6
Dead t ime
High-side
MOSFET
gate drive
1.4
1.2
Low-side
MOSFET
gate drve
1.0
Soft-sta rt
0.8
time
Figure 16. MOSFETs Gate Drive Signal
0.6
60
70
80
90
100
110
2. Internal Oscillator
VCC
150
Rmin
+
S
3V
-
1V
+
R
CT
RSS
Q
CON
CSS
-Q
FAN7621
HV CC
Rmax
I CTC
2I CTC
140
LVCC
RT
I CTC
130
Figure 18. Resonant Converter Typical Gain Curve
FAN7621 employs a current-controlled oscillator, as
shown in Figure 17. Internally, the voltage of RT pin is
regulated at 2V and the charging / discharging current
for the oscillator capacitor, CT, is obtained by copying the
current flowing out of RT pin (ICTC) using a current mirror.
Therefore, the switching frequency increases as ICTC
increases.
VREF
120
Frequency (kHz)
F/F
HO
CTR
LO
-
CS
+
RT
-
2V
8
Counter
(1/4)
SG
PG
Gate drive
R sense
Figure 19. Frequency Control Circuit
Figure 17. Current Controlled Oscillator
The minimum switching frequency is determined as:
f min =
3. Frequency Setting
Figure 18 shows the typical voltage gain curve of a
resonant converter, where the gain is inversely
proportional to the switching frequency in the ZVS
region. The output voltage can be regulated by
modulating the switching frequency. Figure 19 shows the
typical circuit configuration for RT pin, where the optocoupler transistor is connected to the RT pin to modulate
the switching frequency.
© 2009 Fairchild Semiconductor Corporation
FAN7621 • Rev. 1.0.3
5.2k Ω
× 100(kHz )
Rmin
(1)
Assuming the saturation voltage of opto-coupler
transistor is 0.2V, the maximum switching frequency is
determined as:
f max = (
5.2k Ω 4.68k Ω
+
) × 100(kHz )
Rmin
Rmax
(2)
To prevent excessive inrush current and overshoot of
output voltage during startup, increase the voltage gain
of the resonant converter progressively. Since the
voltage gain of the resonant converter is inversely
proportional to the switching frequency, the soft-start is
www.fairchildsemi.com
9
FAN7621 — PFM Controller for Half-Bridge Resonant Converters
Functional Description
5.2k Ω 5.2k Ω
) × 100 + 40 (kHz )
+
Rmin
RSS
LV CC
HV CC
RT
Rmax
R min
RSS
CON
(3)
CSS
It is typical to set the initial (soft-start) frequency of two ~
three times the resonant frequency (fO) of the resonant
network.
SG
PG
(4)
Figure 22. Control Pin Configuration for
Pulse Skipping
ISS
40kHz
Remote On / Off: When an auxiliary power supply is
used for standby, the main power stage using FAN7621
can be shut down by pulling down the control pin
voltage, as shown in Figure 23. R1 and C1 are used to
ensure soft-start when switching resumes.
Control loop
take over
OP1
time
4. Control Pin
C1
The FAN7621 has a control pin for protection, cycle
skipping, and remote on/off. Figure 21 shows the internal
block diagram for control pin.
Main Off
FAN7621
LVCC
RT
IOLP
6
Main
Output
R1
Figure 20. Frequency Sweeping of Soft-Start
CON
CTR
LO
fs
f
HO
CS
The soft-start time is three to four times the RC time
constant. The RC time constant is as follows:
TSS = RSS ⋅ CSS
FAN7621
f ISS = (
VCC
Aux
Output
Rmin
0.4 / 0.6V
+
Stop Switching
+
OLP
5V
-
LVCC
+
23V
-
LVCC good
S
Q
R
-Q
CON
OP1
Auto-restart
protection
OVP
Figure 23. Remote On / Off Circuit
Figure 21. Internal Block of Control Pin
5. Protection Circuits
Protection: When the control pin voltage exceeds 5V,
protection is triggered. Detailed applications are
described in the protection section.
The FAN7621 has several self-protective functions, such
as Overload Protection (OLP), Over-Current Protection
(OCP), Abnormal Over-Current Protection (AOCP),
Over-Voltage Protection (OVP), and Thermal Shutdown
(TSD). OLP, OCP, and OVP are auto-restart mode
protections; while AOCP and TSD are latch-mode
protections, as shown in Figure 24.
Pulse Skipping: FAN7621 stops switching when the
control pin voltage drops below 0.4V and resumes
switching when the control pin voltage rises above 0.6V.
To use pulse-skipping, the control pin should be
connected to the opto-coupler collector pin. The
frequency that causes pulse skipping is given as:
SKIP
=
5.2 k
4.16 k
+
R min
R max
x100(kHz)
© 2009 Fairchild Semiconductor Corporation
FAN7621 • Rev. 1.0.3
5.1
Auto-Restart Mode Protection: Once a fault
condition is detected, switching is terminated and the
MOSFETs remain off. When LVCC falls to the LVCC stop
voltage of 11.3V, the protection is reset. FAN7621
(5)
www.fairchildsemi.com
10
FAN7621 — PFM Controller for Half-Bridge Resonant Converters
implemented by sweeping down the switching frequency
ISS
from an initial high frequency (f ) until the output
voltage is established. The soft-start circuit is made by
connecting R-C series network on the RT pin, as shown
in Figure 19. FAN7621 also has an internal soft-start for
3ms to reduce the current overshoot during the initial
cycles, which adds 40kHz to the initial frequency of the
external soft-start circuit, as shown in Figure 20. The
initial frequency of the soft-start is given as:
5.4
Current Sensing Using Resonant Capacitor
Voltage: For high-power applications, current sensing
using a resistor may not be available due to the severe
power dissipation in the resistor. In that case, indirect
current sensing using the resonant capacitor voltage can
be a good alternative because the amplitude of the
p-p
resonant capacitor voltage (Vcr ) is proportional to the
p-p
resonant current in the primary side (Ip ) as:
5.2
Latch-Mode Protection: Once this protection is
triggered, switching is terminated and the gate output
signals remain off. The latch is reset only when LVCC is
discharged below 5V.
LV CC
12
11/ 14 V
V RE F
-
VCr p − p =
Internal
Bias
Latch
protection
Auto-restart
protection
OLP
S
OVP
LV CC good
CON
20k
R
Q
-Q
Q
S
-Q
R
F/F
F/F
(6)
2π f sCr
To minimize power dissipation, a capacitive voltage
divider is generally used for capacitor voltage sensing,
as shown in Figure 27.
Shutdown
OCP
I p p− p
AOCP
LVCC
CDL
TSD
HV CC
RT
LV CC < 5V
CON
Figure 24. Protection Blocks
FAN7621
LV CC good
+
Ip
HO
CTR
LO
5.3
Current Sensing Using Resistor: FAN7621
senses drain current as a negative voltage, as shown in
Figure 25 and Figure 26. Half-wave sensing allows low
power dissipation in the sensing resistor, while full-wave
sensing has less switching noise in the sensing signal.
CS
SG
PG
CB
Csense
V sense
100
Cr
Ip
LV CC
RT
C DL
CON
V CS
FAN7621
HV CC
HO
VCr
CTR
VCrp-p
I ds
LO
CS
SG
PG
Vsense
V CS
R sense
Vsensepk
CB
=
VCr p− p Csense+ C B
I ds
Vsensepk
= VCON
2
V sensepk
VCON
Vsensepk
Figure 25. Half-Wave Sensing
I ds
tDelay =R dC d
Figure 27. Current Sensing Using Resonant
Capacitor Voltage
V CS
LVCC
5.5
Over-Current Protection (OCP): When the
sensing pin voltage drops below -0.6V, OCP is triggered
and the MOSFETs remain off. This protection has a
shutdown time delay of 1.5µs to prevent premature
shutdown during startup.
RT
C DL
CON
V CS
FAN7621
HV CC
HO
CTR
LO
5.6
Abnormal Over-Current Protection (AOCP): If
the secondary rectifier diodes are shorted, large current
with extremely high di/dt can flow through the MOSFET
before OCP or OLP is triggered. AOCP is triggered
without shutdown delay when the sensing pin voltage
drops below -0.9V. This protection is latch mode and
reset when LVCC is pulled down below 5V.
CS
SG
PG
I ds
R sense
Figure 26. Full-Wave Sensing
© 2009 Fairchild Semiconductor Corporation
FAN7621 • Rev. 1.0.3
www.fairchildsemi.com
11
FAN7621 — PFM Controller for Half-Bridge Resonant Converters
resumes normal operation when LVCC reaches the start
voltage of 14.5V.
VCON =
CB
VCr p − p
2(CB + Csense )
where VCr
voltage.
p-p
6.
PCB Layout Guideline
Duty imbalance problems may occur due to the radiated
noise from main transformer, the inequality of the
secondary-side
leakage
inductances
of
main
transformer, and so on. Among them, it is one of the
dominant reasons that the control components in the
vicinity of RT pin are enclosed by the primary current flow
pattern on PCB layout. The direction of the magnetic
field on the components caused by the primary current
flow is changed when the high-and-low side MOSFET
turns on by turns. The magnetic fields with opposite
direction from each other induce a current through, into,
or out of the RT pin, which makes the turn-on duration of
each MOSFET different. It is strongly recommended to
separate the control components in the vicinity of RT pin
from the primary current flow pattern on PCB layout.
Figure 28 shows an example for the duty-balanced case.
The yellow and blue lines show the primary current flows
when the lower-side and higher-side MOSFETs turns on,
respectively. The primary current does not enclose any
component of controller.
(7)
is the amplitude of the resonant capacitor
5.8
Over-Voltage Protection (OVP): When the
LVCC reaches 23V, OVP is triggered. This protection is
used when auxiliary winding of the transformer to supply
VCC to the controller is utilized.
It is helpful to reduce the duty imbalance to make the
loop configured between CON pin and opto-coupler as
small as possible, as shown in the red line in Figure 28.
5.9
Thermal Shutdown (TSD): If the temperature
of the junction exceeds approximately 130°C, the
thermal shutdown triggers.
Figure 28. Example for Duty Balancing
© 2009 Fairchild Semiconductor Corporation
FAN7621 • Rev. 1.0.3
www.fairchildsemi.com
12
FAN7621 — PFM Controller for Half-Bridge Resonant Converters
5.7
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 power
supply. However, even when the power supply is in the
normal condition, the overload situation can occur during
the load transition. To avoid premature triggering of
protection, the overload protection circuit should be
designed to trigger only after a specified time to
determine whether it is a transient situation or a true
overload situation. Figure 27 shows a typical overload
protection circuit. By sensing the resonant capacitor
voltage on the control pin, the overload protection can be
implemented. Using RC time constant, shutdown delay
can be also introduced. The voltage obtained on the
control pin is given as:
Application
Device
Input Voltage Range
Rated Output Power
Output Voltage
(Rated Current)
LCD TV
FAN7621
390VDC
(340~400VDC)
200W
24V-8.3A
Features
High efficiency ( >94% at 400VDC input)
Reduced EMI noise through zero-voltage-switching (ZVS)
Enhanced system reliability with various protection functions
FAN7621
Figure 29. Typical Application Circuit
© 2009 Fairchild Semiconductor Corporation
FAN7621 • Rev. 1.0.3
www.fairchildsemi.com
13
FAN7621 — PFM Controller for Half-Bridge Resonant Converters
Typical Application Circuit (Half-Bridge LLC Resonant Converter)
Usually, LLC resonant converters require large leakage inductance value. To obtain a large leakage inductance,
sectional winding method is used.
2
Core: EC35 (Ae=106 mm )
Bobbin: EC35 (Horizontal)
Transformer Model Number: SNX-2468-1
EC35
2
Np
13 N
s2
12 N
s1
10
6
9
Figure 30. Transformer Construction
Pins (S → F)
Wire
Turns
Note
Np
6→2
0.08φ×88 (Litz Wire)
36
Ns1
12 → 9
0.08φ×234 (Litz Wire)
4
Bifilar Winding
Ns2
10 → 13
0.08φ×234 (Litz Wire)
4
Bifilar Winding
Pins
Specifications
Remark
Primary-Side Inductance (Lp)
2-6
550μH ± 10%
100kHz, 1V
Primary-Side Effective Leakage (Lr)
2-6
110μH ± 10%
Short one of the secondary windings
For more detailed information regarding the transformer, visit http://www.santronics-usa.com/documents.html or
contact sales@santronics-usa.com or +1-408-734-1878 (Sunnyvale, California USA).
© 2009 Fairchild Semiconductor Corporation
FAN7621 • Rev. 1.0.3
www.fairchildsemi.com
14
FAN7621 — PFM Controller for Half-Bridge Resonant Converters
Typical Application Circuit (Continued)
10.30
10.10
-A-
0.47 TYP
16
9
16 15
10 9
5.01 TYP
5.40
5.20 -B-
7.8
9.27 TYP
1
2
7
8
3.9
1
0.2 C B A
ALL LEAD TIPS
8
1.27
TYP
PIN #1 IDENT.
ALL LEAD TIPS
0.1 C
0.60 TYP
SEE DETAIL A
0.16 1.90
0.14 1.70
2.1 MAX
0.25
0.15
0.51
0.35
1.27 TYP
0.12
7° TYP
GAGE PLANE
0-8° TYP
MIN
0.25
(2.13 TYP)
0.25
SEATING PLANE
1.25
C A
NOTES:
A. CONFORMS TO EIAJ EDR-7320
REGISTRATION, ESTABLISHED IN
DECEMBER, 1998.
B. DIMENSIONS ARE IN MILLIMETERS.
C. DIMENSIONS ARE EXCLUSIVE OF BURRS,
MOLD FLASH, AND TIE BAR EXTRUSIONS.
D. DRAWING FILENAME: MKT-M16Drev5
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