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FAN7621B
PFM Controller for Half-Bridge Resonant Converters
Features
Description
The FAN7621B 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 FAN7621B
simplifies designs and improves productivity, while
improving performance. The FAN7621B includes a highside gate-drive 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 FAN7621B 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
FAN7621BSJ
FAN7621BSJX
© 2009 Fairchild Semiconductor Corporation
FAN7621B • Rev. 1.0.1
-40°C ~ 130°C
Package
16-Lead Small Outline Package (SOP)
Packaging
Method
Tube
Tape & Reel
www.fairchildsemi.com
FAN7621B — PFM Controller for Half-Bridge Resonant Converters
July 2010
D1
Cr
Llk
VCC
Np
Lm
LVCC
CON
C DL
VIN
FAN7621B
HVCC
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
2ICTC
3V
-
1V
+
S
Q
R
-Q
10.0 / 12.5 V
LVCC good
VREF
-
HVCC good
Internal
Bias
8.7 / 9.2 V
+
ICTC
+
-
+
ICTC
VREF
F/F
1
-
2V
Time
Delay
+
-
RT
CON
350ns
8
Coun ter (1/4)
LVCC
IOLP
6
-
Time
Delay
+
350ns
0.4 / 0.6 V
OLP
5V
High-Side
Gate Drive
Level-Shift
+
-
LVCC
+
23 V
-
LVCC good
OVP
S
Q
R
-Q
Auto-restart
protection
Low-Side
Gate Drive
Balancing
Delay
HVCC
3
HO
2
CTR
14
LO
Shutdown without delay
-1
+
Q
S
-Q
R
50ns delay
0.9 V
-
VAOCP
TSD
Latch
protection
LVCC < 5V
Delay
1.5μs
-
16
PG
10
SG
VOCP
0.58 V
+
9
CS
Figure 2. Internal Block Diagram
© 2009 Fairchild Semiconductor Corporation
FAN7621B • Rev. 1.0.1
www.fairchildsemi.com
2
FAN7621B — PFM Controller for Half-Bridge Resonant Converters
Application Circuit Diagram
(1) HVCC
PG (16)
(2) CTR
NC (15)
(3) HO
LO (14)
(4) NC
NC (13)
FAN7621B
(5) NC
LVCC (12)
(6) CON
NC (11)
(7) NC
SG (10)
CS (9)
(8) RT
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
This pin is the supply voltage of the control IC.
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.
© 2009 Fairchild Semiconductor Corporation
FAN7621B • Rev. 1.0.1
www.fairchildsemi.com
3
FAN7621B — PFM Controller for Half-Bridge Resonant Converters
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
Min.
Max.
VHO
High-Side Gate Driving Voltage
VCTR-0.3
HVCC
VLO
Low-Side Gate Driving Voltage
-0.3
LVCC
LVCC
Low-Side Supply Voltage
HVCC to VCTR High-Side VCC Pin to Center Voltage
Unit
V
-0.3
25.0
V
-0.3
25.0
V
-0.3
600.0
V
VCTR
Center Voltage
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
50
V/ns
1.13
W
dVCTR/dt
PD
TJ
TSTG
Allowable Center Voltage Slew Rate
Total Power Dissipation
16-SOP
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
FAN7621B • Rev. 1.0.1
16-SOP
Value
Unit
110
ºC/W
www.fairchildsemi.com
4
FAN7621B — 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)
11.2
12.5
13.8
V
LVCCUV-
LVCC Supply Under-Voltage Negative Going Threshold (LVCC Stop)
8.90
10.00
11.10
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
2.5
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
140
fSS=fOSC+40kHz, RT=5.2kΩ
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
FAN7621B • Rev. 1.0.1
CLoad=1nF, HVCC=17V
1.0
V
0.6
V
1.0
V
0.6
V
IO=20mA
www.fairchildsemi.com
5
FAN7621B — 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
FAN7621B • Rev. 1.0.1
www.fairchildsemi.com
6
FAN7621B — 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
Temp (OC)
Figure 4. Low-Side MOSFET Duty Cycle
vs. Temperature
50
75
100
Figure 5. Switching Frequency vs. Temperature
1.1
1.1
1.05
1.05
Normalized at 25OC
Normalized at 25OC
25
Temp (OC)
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
-50
100
Figure 8. Low-Side VCC (LVCC) Start vs. Temperature
© 2009 Fairchild Semiconductor Corporation
FAN7621B • Rev. 1.0.1
-25
0
25
50
75
100
Temp (OC)
(OC)
Figure 9. Low-Side VCC (LVCC) Stop vs. Temperature
www.fairchildsemi.com
7
FAN7621B — 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
0.9
1
0.95
0.9
-50
-25
0
25
50
75
100
-50
-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
FAN7621B • Rev. 1.0.1
www.fairchildsemi.com
8
FAN7621B — PFM Controller for Half-Bridge Resonant Converters
Typical Performance Characteristics (Continued)
1. Basic Operation: FAN7621B 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.
Gain
1.8
f
min
f max
f normal
f ISS
Dead t ime
1.6
High-side
MOSFET
gate drive
1.4
1.2
Low-side
MOSFET
gate drve
1.0
time
Soft-sta rt
Figure 16. MOSFETs Gate Drive Signal
0.8
2. Internal Oscillator: FAN7621B employs a currentcontrolled 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.
100
110
1V
S
Q
R
-Q
RT
+
F/F
8
Counter
(1/4)
140
150
HVCC
Rmax
Rmin
R SS
C SS
2V
130
LVCC
-
CT
120
Figure 18. Resonant Converter Typical Gain Curve
+
RT
90
Frequency (kHz)
-
-
80
FAN7621B
2I CTC
70
+
3V
I CTC
60
VCC
I CTC
VREF
0.6
CON
HO
CTR
LO
Gate drive
CS
SG
Figure 17. Current Controlled Oscillator
PG
Rsense
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
opto-coupler transistor is connected to the RT pin to
modulate the switching frequency.
Figure 19. Frequency Control Circuit
The minimum switching frequency is determined as:
f min =
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
© 2009 Fairchild Semiconductor Corporation
FAN7621B • Rev. 1.0.1
www.fairchildsemi.com
9
FAN7621B — PFM Controller for Half-Bridge Resonant Converters
Functional Description
5.2k Ω 5.2k Ω
) × 100 + 40 (kHz )
=(
+
Rmin
RSS
5.2 k
4.16 k
+
R min
R max
x100(kHz)
VCC
(5)
LVCC
HVCC
RT
(3)
Rm ax
It is typical to set the initial (soft-start) frequency of two ~
three times the resonant frequency (fO) of the resonant
network.
Rm in
RSS
CSS
CON
HO
CTR
LO
The soft-start time is three to four times the RC time
constant. The RC time constant is as follows:
TSS = RSS ⋅ CSS
=
FAN7621B
f
ISS
SKIP
CS
(4)
SG
PG
fs
f
ISS
40kHz
Figure 22. Control Pin Configuration for Pulse
Skipping
Control loop
take over
Remote On / Off: When an auxiliary power supply is
used for standby, the main power stage using
FAN7621B 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.
time
Figure 20. Frequency Sweeping of Soft-Start
4. Control Pin: The FAN7621B has a control pin for
protection, cycle skipping, and remote on/off. Figure 21
shows the internal block diagram for control pin.
LVCC
CON
IOLP
6
0.4 / 0.6V
+
Stop Switching
+
OLP
5V
-
LVCC
+
23V
-
LVCC good
S
Q
R
-Q
Auto-restart
protection
OVP
Figure 21. Internal Block of Control Pin
Protection: When the control pin voltage exceeds 5V,
protection is triggered. Detailed applications are
described in the protection section.
Pulse Skipping: FAN7621B 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:
© 2009 Fairchild Semiconductor Corporation
FAN7621B • Rev. 1.0.1
Figure 23. Remote On / Off Circuit
5. Protection Circuits: The FAN7621B has several selfprotective 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.
www.fairchildsemi.com
10
FAN7621B — PFM Controller for Half-Bridge Resonant Converters
proportional to the switching frequency, the soft-start is
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. FAN7621B 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:
I ds
RT
CDL
CON
VCS
LVCC
FAN7621B
HV
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.
1 0 / 12.5V
CTR
PG
Internal
Bias
V RE F
-
Ids
Latch
protec tion
Aut o-restart
protec tion
OLP
OV P
L VCC good
S
Q
R
-Q
S
-Q
R
F/F
F/F
20k
Q
Rsense
Figure 26. Full-Wave Sensing
Shutdo wn
O CP
CON
HO
LO
SG
LVCC good
CC
CS
12
+
VCS
LV CC
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 resonant
p-p
capacitor voltage (Vcr ) is proportional to the resonant
p-p
current in the primary side (Ip ) as:
AOCP
TSD
LVCC < 5V
Figure 24. Protection Blocks
VCr p − p =
Current Sensing Using Resistor: FAN7621B 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.
I p p− p
2π f sCr
(6)
LV CC
CDL
CON
VCS
FAN7621B
HVCC
RT
CT R
I ds
LO
CS
SG
Rsense
HO
PG
VCS
I ds
Figure 25. Half-Wave Sensing
© 2009 Fairchild Semiconductor Corporation
FAN7621B • Rev. 1.0.1
www.fairchildsemi.com
11
FAN7621B — PFM Controller for Half-Bridge Resonant Converters
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
10.0V, the protection is reset. FAN7621B resumes
normal operation when LVCC reaches the start voltage of
12.5V.
5.2 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.
LVCC
CDL
RT
CON
FAN7621B
HVCC
5.3 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:
Ip
HO
CTR
LO
CS
SG
PG
CB
C sense
100
Vsense
Ip
VCON =
where VCr
voltage.
VCr
VCrp-p
Vsense
CB
VCr p − p
2(CB + Csense )
Vsense pk
CB
=
VCr p − p Csense + CB
p-p
(7)
is the amplitude of the resonant capacitor
5.4 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.
Vsense pk
= VCON
2
5.5 Thermal Shutdown (TSD): If the temperature of the
junction exceeds approximately 130°C, the thermal
shutdown triggers.
Vsensepk
VCON
Vsensepk
Tdelay = Rd Cd
Figure 27. Current Sensing Using Resonant
Capacitor Voltage
5.1 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.
© 2009 Fairchild Semiconductor Corporation
FAN7621B • Rev. 1.0.1
www.fairchildsemi.com
12
FAN7621B — PFM Controller for Half-Bridge Resonant Converters
To minimize power dissipation, a capacitive voltage
divider is generally used for capacitor voltage sensing,
as shown in Figure 27.
In addition, it is helpful to reduce the duty imbalance to
make the loop configured between CON pin and optocoupler as small as possible, as shown in the red line in
Figure 28.
Figure 28. Example for Duty Balancing
© 2009 Fairchild Semiconductor Corporation
FAN7621B • Rev. 1.0.1
www.fairchildsemi.com
13
FAN7621B — PFM Controller for Half-Bridge Resonant Converters
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 turnon 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 dutybalanced case. The yellow and blue lines show the
primary current flows when the lower-side and higherside MOSFETs turns on, respectively. The primary
current does not enclose any component of controller.
Application
Device
Input Voltage Range
Rated Output Power
Output Voltage
(Rated Current)
LCD TV
FAN7621B
390VDC
(340~400VDC)
192W
24V-8A
Features
High efficiency ( >94% at 400VDC input)
Reduced EMI noise through zero-voltage-switching (ZVS)
Enhanced system reliability with various protection functions
C110
open
D101
1N4937
R103 400k
Vcc=16~ 20Vdc
C102
22nF
EER3542
D202
FYPF2010DN
C201
C202
2000uF / 2000uF/
35V
35V
U5
R108
10k
LVcc
ZD101
6.8V
R111
45k
HVcc
RT
R104
5.1k
R107
7.7k
C111
680pF
CON
C107
10uF
C101
220uF/ 450V
Vin=340~400Vdc
R105
7.5k
C104
open
U2
Vo
C105
0.33uF
U4
R110
1M
F101
3.15A/250V
JP5
0
R112
10k
D102
1N4148
FAN7621
R109
1M
Q1
FCPF11N60F
R113
3.3
CTR
R115
10k
R114
3.3
CS
R102
1k
C103
100pF
SG
C204
12nF
U2
R202
D201
FYPF2010DN 1k
JP1, 0
JP2, 0
D102
1N4148
R204
62k
R205
2k
JP3, 0
JP4, 0
LO
C108
12nF
R201
10k
C106
150nF
HO
R116
10k
C203
47nF
Q2
FCPF11N60F
R203
33k
C301
R205
7k
PG
R101
0.2
Figure 29. Typical Application Circuit
© 2009 Fairchild Semiconductor Corporation
FAN7621B • Rev. 1.0.1
www.fairchildsemi.com
14
FAN7621B — 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
FAN7621B • Rev. 1.0.1
www.fairchildsemi.com
15
FAN7621B — 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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