FAN7621S — PFM Controller for Half-Bridge Resonant Converters
July 2010
FAN7621S
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
Auto-Restart Operation for All Protections with
an External LV
CC
Protection Functions: Over-Voltage Protection
(OVP), Over-Current Protection (OCP), Abnormal
Over-Current Protection (AOCP), Internal Thermal
Shutdown (TSD)
Description
The FAN7621S 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 FAN7621S
simplifies designs and improves productivity, while
improving performance. The FAN7621S 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
significantly improves efficiency. The ZVS also reduces
the switching noise noticeably, which allows a small-
sized Electromagnetic Interference (EMI) filter.
The FAN7621S 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
FAN7621SSJ
FAN7621SSJX
Operating Junction
Temperature
-40°C to +130°C
Package
16-Lead, Small Outline Package (SOP)
Packaging
Method
Tube
Tape & Reel
© 2009 Fairchild Semiconductor Corporation
FAN7621S • Rev. 1.0.1
www.fairchildsemi.com
FAN7621S — PFM Controller for Half-Bridge Resonant Converters
Application Circuit Diagram
Cr
V
IN
V
CC
V
O
LV
CC
HV
CC
Rmin
Rmax
Rss
Css
FAN7621S
R
T
AR
CS
HO
CTR
LO
SG PG
Figure 1. Typical Application Circuit (LLC Resonant Half-Bridge Converter)
Block Diagram
LV
CC
12
V
re f
I
R T
I
R T
3V
2I
R T
2V
1V
S
R
V
re f
1
LV
Q
L U V+ / L U V-
CC
HVcc
g o od
V
r e f
In tern al
B ias
H UV+ / H UV-
Level
S hifter
R
T
8
T ime
D elay
350ns
D ivider
H ig h S id e
Gate D river
3
2
HO
CTR
LO
AR
6
5k
V
C s s H
/ V
C s s L
T ime
D elay
350ns
B alan cin g
D elay
L ow S id e
Gate D river
14
S
LV
g o od
R
Q
Sh utd own with o ut d elay
CC
TS D
L V
C C
V
O V P
V
A O C P
D elay
50n s
V
O C P
D elay
1.5µs
16
PG
SG
-1
10
9
CS
Figure 2. Internal Block Diagram
© 2009 Fairchild Semiconductor Corporation
FAN7621S • Rev. 1.0.1
www.fairchildsemi.com
2
FAN7621S — PFM Controller for Half-Bridge Resonant Converters
Pin Configuration
(1) H V
CC
(2) C T R
(3) H O
(4) N C
(5) N C
(6) A R
(7) N C
(8) R
T
Figure 3. Package Diagram
P G (16 )
N C (15 )
L O (14 )
FAN7 6 21S
N C (13 )
L V
C C
(12 )
N C (11 )
S G (10 )
CS
(9)
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
AR
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 discharging the external soft-start capacitor when any protection is triggered.
When the voltage of this pin drops to 0.2V, all protections are reset and the controller starts
to operate again.
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
FAN7621S • Rev. 1.0.1
www.fairchildsemi.com
3
FAN7621S — 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
AR
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
Auto-Restart Pin Input Voltage
Current Sense (CS) Pin Input Voltage
R
T
Pin Input Voltage
Allowable Center Voltage Slew Rate
Total Power Dissipation
Maximum Junction Temperature
Storage Temperature Range
(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
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
Value
110
Unit
ºC/W
© 2009 Fairchild Semiconductor Corporation
FAN7621S • Rev. 1.0.1
www.fairchildsemi.com
4
FAN7621S — 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
I
O
LV
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, C
Load
=1nF
No Switching
f
OSC
=100kHz, C
Load
=1nF
No Switching
Min.
Typ.
Max.
Unit
μA
μA
μA
mA
μA
mA
mA
50
50
100
5
100
6
2
120
200
8
200
9
4
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
8.9
12.5
10.0
2.5
9.2
8.7
0.5
10.2
9.6
13.8
11.1
V
V
V
V
V
V
Oscillator & Feedback Section
V
RT
f
OSC
DC
f
SS
t
SS
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
1.5
94
48
2.0
100
50
140
3
4
2.5
106
52
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
FAN7621S • Rev. 1.0.1
www.fairchildsemi.com
5
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