Product Specification
Synchronous Rectifier Controller for Flyback Converter
SG6203
System General Corp. - 2 - www.sg.com.tw
Version1.0 (IAO33.0019.B3) Dec.23, 2005
FEATURES DESCRIPTION
Low operation current (1.7mA)
One resistor for timing setting
Internal automatic tracking for optimum dead time
No reverse energy flow at light load
Best suited for primary green mode PWM IC
Wide supply voltage range from 6V to 20V
Built in 18V Zener diode
Optional current sensing:
Current shunt
RC network for better efficiency
APPLICATIONS
Flyback converters, such as
Power adaptors
Open frame SMPS
The SG6203 is designed to control and drive the
synchronous rectifier for the flyback converter. The
synchronous signal of the primary switch is obtained by a
single diode connected between the transformer
secondary winding and the SG6203. Using the SG6203,
no additional transformer winding is required and the
circuit complexity can be minimized.
No matter, the power unit is operated under
discontinuous conduction mode (DCM) or continuous
conduction mode (CCM), the SG6203 can operate
properly. The so called "shoot through" or "cross
conduction" problem in CCM and the energy reverse
problem from the secondary to the primary in DCM will
not happen.
TYPICAL APPLICATION
Product Specification
Synchronous Rectifier Controller for Flyback Converter
SG6203
System General Corp. - 1 - www.sg.com.tw
Version1.0 (IAO33.0019.B3) Dec.23, 2005
MARKING DIAGRAMS PIN CONFIGURATION
ORDERING INFORMATION
Part Number
Package
SG6203SZ
8-Pin SOP (Lead Free)
SG6203DZ
8-Pin DIP (Lead Free)
PIN DESCRIPTIONS
Pin No.
Name
Function
1
Vcc
Supply voltage of gate driver and control circuits.
2 Output
Totem-pole output to drive the synchronous power MOSFET. When the voltage on DET pin
falls below 1.4V from above 2.1V, the synchronous MSOFET will be turned on. To prevent the
reversed energy flow, this pin will be disabled once the voltage on IN+ pin is lower than that of
IN- pin or internal one shot timer is terminated.
3 GND
The power ground and signal ground. A 0.1uF decoupling capacitor placed between Vcc and
GND is recommended.
4 VZ
Built in 18V Zener diode. When the flyback output voltage is higher than 18V, this pin can be
used to provide a stable 18V to Vcc pin. If the flyback output voltage is lower than 18V, this pin
can be left open and connect the output voltage directly to Vcc pin.
5 DET
Connecting a diode from this pin to the transformer secondary winding, this pin can provide
on/off information of the primary switch. Low DET level indicates the secondary rectifier is
conducted, therefore the synchronous MOSFET should be turnd on. DET will stay high when
the primary switch is conducting or secondary rectifier turns off, and the synchronous MOSFET
should be turned off.
6 RT
Current reference. Connecting a resistor from this pin to ground can program the internal
current reference IRT. Three internal current sources, which are IIN+, IIN- ,and Idet, are then
mirrored from IRT. IRT determines the duration of internal one shot signal, and then the
maximum on time of the synchronous MOSFET is obtained by subtracting the on time of the
primary switch from the one shot signal duration. If the resistor is too small, the synchronous
MOSFET may be turned off even when the secondary rectifier is still conducting, and hence
decreases the system efficiency. However, if the resistor is too large, the Output will be shut off
immediately once DET gets high. In SG6203, an internal phase locked loop will modulate the
duration of the internal one shot signal to maintain a suitable dead time between the primary
switch and the synchronous MOSFET.
7 IN-
The inverting input of the current sense comparator. In discontinuous conduction mode, the
secondary rectifier will turn off before the next switching cycle of the primary switch. Once the
secondary rectifier is off, the synchronous MOSFET must be turned off to prevent the reversed
energy flow. A resistor connected between IN+ and IN- can used to develop the zero current
crossing signal of the secondary rectifier. Once the voltage on IN+ is lower than IN-, the Output
will be pulled low.
T
: D = DIP, S = SOP
P :
Z =Lead Free + ROHS
Compatible
XXXXXXXX
: Wafer Lot
Y
: Year;
WW
: Week
V
: Assembly Location
VZ
GND
IN+
IN-
RT
DET
V
CC
Output
SG6203TP
XXXXXXXXYWWV
Product Specification
Synchronous Rectifier Controller for Flyback Converter
SG6203
System General Corp. - 2 - www.sg.com.tw
Version1.0(IAO33.0010.B1) Dec. 23, 2005
8 IN+
The non-inverting input of the current sense comparator. In discontinuous conduction mode,
the secondary rectifier will turn off before the next switching cycle of the primary switch. Once,
the secondary rectifier is off, the synchronous MOSFET must be turned off to prevent the
reversed energy flow. A resistor connected between IN+ and IN- can used to develop the zero
current crossing signal of the secondary rectifier. Once the voltage on IN+ is lower than IN-, the
Output will be pulled low.
Product Specification
Synchronous Rectifier Controller for Flyback Converter
SG6203
System General Corp. - 3 - www.sg.com.tw
Version1.0(IAO33.0010.B1) Dec. 23, 2005
BLOCK DIAGRAM
Product Specification
Synchronous Rectifier Controller for Flyback Converter
SG6203
System General Corp. - 4 - www.sg.com.tw
Version1.0(IAO33.0010.B1) Dec. 23, 2005
ABSOLUTE MAXIMUM RATINGS
Symbol Parameter
Value
Unit
Vcc
DC Supply Voltage*
25
V
Iout
Gate Output Current
500
mA
V
H
DET, OUT, VZ
-0.3 to 25
V
V
L
RT, IN+, IN-
-0.3 to 7
V
P
D
Power
Dissipation
SOP8
DIP8
400
800
mW
R
JA
Thermal Resistance (Junction to Air)
SOP8
DIP8
208.4
82.5
C/W
T
J
Operating Junction Temperature
150
C
T
STG
Storage Temperature Range
-65 to +150
C
T
L
Lead Temperature (Soldering)
10 sec
300
C
ESD Capability, Human Body Model
2.0
KV
ESD Capability, Machine Model
200
V
* All voltage values, except differential voltages, are given with respect to GND pin.
* Stresses beyond those listed under "absolute maximum ratings" may cause permanent damage to the
device.
RECOMMENDED OPERATING CONDITIONS
Symbol Parameter
Value
Unit
Vcc
DC Supply Voltage
<20 V
T
A
Operating Ambient Temperature
-30~85
C
RT
Pulse width of the one-shot signal
12~36
K
ELECTRICAL CHARACTERISTICS V
CC
= 12V; RT
= 24K ; T
A
= 25C, unless noted
Timing Control Section
Symbol Parameter
Test
Condition Min.
Typ.
Max.
Unit
V
RT
Voltage on RT pin
1.14
1.2
1.26
V
RT=12K
6.5 7.5 8.5 uS
RT=24K
13 15 17 uS
T
RT
Pulse width of the one-shot signal
RT=36K
19.5 22.5 25.5 uS
T
RT
Adjustable range of the pulse width compared
to T
RT
RT=12K; RT=24K;
RT=36K
+40 +60 +80 %
T
DEAD
Timing margin between turn off of output
(Output falling) and start of the next switching
cycle (DET rising)
200
1000
nS
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