FAN7621B — PFM Controller for Half-Bridge Resonant Converters
July 2010
FAN7621B
PFM Controller for Half-Bridge Resonant Converters
Features
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)
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 high-
side 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.
The FAN7621B can be applied to various resonant
converter topologies; such as series resonant, parallel
resonant, and LLC resonant converters.
Applications
PDP and LCD TVs
Desktop PCs and Servers
Adapters
Telecom Power Supplies
Video Game Consoles
Related Resources
AN4151 — Half-bridge LLC Resonant Converter Design
TM
using FSFR-series Fairchild Power Switch (FPS )
Ordering Information
Part Number
FAN7621BSJ
FAN7621BSJX
Operating Junction
Temperature
-40°C ~ 130°C
Package
16-Lead Small Outline Package (SOP)
Packaging
Method
Tube
Tape & Reel
© 2009 Fairchild Semiconductor Corporation
FAN7621B • Rev. 1.0.1
www.fairchildsemi.com
FAN7621B — PFM Controller for Half-Bridge Resonant Converters
Application Circuit Diagram
Cr
L
lk
V
CC
LVCC
HV
CC
RT
D1
Np
Ns
V
O
Lm
Ns
C
F
R
F
FAN7621B
HO
CTR
LO
V
IN
C
DL
CON
D2
KA431
CS
SG
PG
R
sense
Figure 1. Typical Application Circuit (LLC Resonant Half-Bridge Converter)
Block Diagram
LV
CC
12
+
V
REF
I
CTC
I
CTC
3V
LV
CC
good
Internal
Bias
+
-
+
1V
F/F
Time
Delay
Level-Shift
-
2V
R
T
CON
8
350ns
Coun ter (1/4)
High-Side
Gate Drive
LV
CC
I
OLP
6
0.4 / 0.6 V
+
+
-
Time
Delay
Balancing
Delay
Low-Side
Gate Drive
350ns
Shutdown without delay
+
OLP
5V
-
S
Q
-Q
Q
-Q
S
R
LV
CC
23 V
+
LV
CC
good
R
-1
0.9 V
50ns delay
-
-
OVP
Auto-restart
protection
V
AOCP
TSD
LV
CC
< 5V
Delay
1.5μs
-
Latch
protection
V
OCP
0.58 V
+
9
CS
Figure 2. Internal Block Diagram
© 2009 Fairchild Semiconductor Corporation
FAN7621B • Rev. 1.0.1
2
+
2I
CTC
R
-Q
-
1
S
Q
10.0 / 12.5 V
-
V
REF
HV
CC
good
8.7 / 9.2 V
HV
CC
HO
CTR
LO
+
-
3
2
14
16
PG
SG
10
www.fairchildsemi.com
FAN7621B — PFM Controller for Half-Bridge Resonant Converters
Pin Configuration
(1) HV
CC
(2) CTR
(3) HO
(4) NC
(5) NC
(6) CON
(7) NC
(8) R
T
PG (16)
NC (15)
LO (14)
FAN7621B
NC (13)
LV
CC
(12)
NC (11)
SG (10)
CS (9)
Figure 3. Package Diagram
Pin Definitions
Pin #
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Name
HV
CC
CTR
HO
NC
NC
CON
NC
R
T
CS
SG
NC
LV
CC
NC
LO
NC
PG
Description
This is the supply voltage of the high-side gate-drive circuit IC.
This is the drain of the low-side MOSFET. Typically, a transformer is connected to this pin.
This is the high-side gate driving signal.
No connection.
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.
No connection.
This pin programs the switching frequency. Typically, an opto-coupler is connected to
control the switching frequency for the output voltage regulation.
This pin senses the current flowing through the low-side MOSFET. Typically, negative
voltage is applied on this pin.
This pin is the control ground.
No connection.
This pin is the supply voltage of the control IC.
No connection.
This is the low-side gate driving signal.
No connection.
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
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. T
A
=25°C unless otherwise specified.
Symbol
V
HO
V
LO
LV
CC
V
CTR
V
CON
V
CS
V
RT
dV
CTR
/dt
P
D
T
J
T
STG
Parameter
High-Side Gate Driving Voltage
Low-Side Gate Driving Voltage
Low-Side Supply Voltage
Center Voltage
Control Pin Input Voltage
Current Sense (CS) Pin Input Voltage
R
T
Pin Input Voltage
Allowable Center Voltage Slew Rate
Total Power Dissipation
16-SOP
(1)
(1)
Min.
V
CTR
-0.3
-0.3
-0.3
-0.3
-0.3
-0.3
-5.0
-0.3
Max.
HV
CC
LV
CC
25.0
25.0
600.0
LV
CC
1.0
5.0
50
1.13
+150
Unit
V
V
V
V
V
V
V
V/ns
W
°C
°C
HV
CC
to V
CTR
High-Side V
CC
Pin to Center Voltage
Maximum Junction Temperature
Storage Temperature Range
Recommended Operating Junction Temperature
-40
-55
+130
+150
Note:
1. The maximum value of the recommended operating junction temperature is limited by thermal shutdown.
Thermal Impedance
Symbol
θ
JA
Parameter
Junction-to-Ambient Thermal Impedance
16-SOP
Value
110
Unit
ºC/W
© 2009 Fairchild Semiconductor Corporation
FAN7621B • Rev. 1.0.1
www.fairchildsemi.com
4
FAN7621B — PFM Controller for Half-Bridge Resonant Converters
Electrical Characteristics
T
A
=25°C and LV
CC
=17V unless otherwise specified.
Symbol
Supply Section
I
LK
I
Q
HV
CC
I
Q
LV
CC
I
O
HV
CC
Parameter
Offset Supply Leakage Current
Quiescent HV
CC
Supply Current
Quiescent LV
CC
Supply Current
Operating HV
CC
Supply Current
(RMS Value)
Operating LV
CC
Supply Current
(RMS Value)
Test Conditions
HV
CC
=V
CTR
(HV
CC
UV+) - 0.1V
(LV
CC
UV+) - 0.1V
f
OSC
=100kHz, V
CON
> 0.6V,
C
Load
=1nF
No Switching, V
CON
< 0.4V
f
OSC
=100kHz, V
CON
> 0.6V,
C
Load
=1nF
No Switching, V
CON
< 0.4V
Min.
Typ.
Max.
Unit
μA
μA
μA
mA
μA
mA
mA
50
50
100
5
100
6
2
120
200
8
200
9
4
I
O
LV
CC
UVLO Section
LV
CC
UV+
LV
CC
UV-
LV
CC
UVH
HV
CC
UV+
HV
CC
UV-
HV
CC
UVH
LV
CC
Supply Under-Voltage Positive Going Threshold (LV
CC
Start)
LV
CC
Supply Under-Voltage Negative Going Threshold (LV
CC
Stop)
LV
CC
Supply Under-Voltage Hysteresis
HV
CC
Supply Under-Voltage Positive Going Threshold (HV
CC
Start)
HV
CC
Supply Under-Voltage Negative Going Threshold (HV
CC
Stop)
HV
CC
Supply Under-Voltage Hysteresis
8.2
7.8
11.2
8.90
12.5
10.00
2.5
9.2
8.7
0.5
10.2
9.6
13.8
11.10
V
V
V
V
V
V
Oscillator & Feedback Section
V
CONDIS
V
CONEN
V
RT
f
OSC
DC
f
SS
t
SS
Control Pin Disable Threshold Voltage
Control Pin Enable Threshold Voltage
V-I Converter Threshold Voltage
Output Oscillation Frequency
Output Duty Cycle
Internal Soft-Start Initial Frequency
Internal Soft-Start Time
f
SS
=f
OSC
+40kHz, R
T
=5.2kΩ
2
R
T
=5.2kΩ
0.36
0.54
1.5
94
48
0.40
0.60
2.0
100
50
140
3
4
0.44
0.66
2.5
106
52
V
V
V
kHz
%
kHz
ms
Output Section
I
source
I
sink
t
r
t
f
V
HOH
V
HOL
V
LOH
V
LOL
Peak Sourcing Current
Peak Sinking Current
Rising Time
Falling Time
High Level of High-Side Gate Driving
Signal (V
HVCC
-V
HO
)
Low Level of High-Side Gate Driving
Signal
High Level of High-Side Gate Driving
Signal (V
LVCC
-V
LO
)
Low Level of High-Side Gate Driving
Signal
HV
CC
=17V
HV
CC
=17V
C
Load
=1nF, HV
CC
=17V
250
460
360
600
65
35
1.0
0.6
I
O
=20mA
1.0
0.6
V
V
mA
mA
ns
ns
V
V
© 2009 Fairchild Semiconductor Corporation
FAN7621B • Rev. 1.0.1
www.fairchildsemi.com
5
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