Product Specification
Synchronous Rectifier Controller for Flyback Converter
SG6203
FEATURES
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
DESCRIPTION
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.
The power unit can be properly operated under
discontinuous conduction mode (DCM) or continuous
conduction mode (CCM). Problems such as
“shoot-through” or “cross conduction” in CCM and
energy-reverse from the secondary to the primary in DCM
are prevented by the SG6203 design.
APPLICATIONS
Flyback converters, such as:
Power adaptors
Open-frame SMPS
TYPICAL APPLICATION
© System General Corp.
Version 1.0.1 (IAO33.0010.B1)
-1-
www.sg.com.tw • www.fairchildsemi.com
September 24, 2007
Product Specification
Synchronous Rectifier Controller for Flyback Converter
SG6203
PIN CONFIGURATION
MARKING DIAGRAMS
SG6203TP
XXXXXXXXYWWV
T:
D=DIP, S=SOP
P :
Z=Lead Free + ROHS
Compatible
XXXXXXXX:
Wafer Lot
Y:
Year;
WW:
Week
V:
Assembly Location
V
CC
Output
GND
VZ
IN+
IN-
RT
DET
ORDERING INFORMATION
Part Number
SG6203SZ
SG6203DZ
Pb-Free
Package
8-Pin SOP
8-Pin DIP
PIN DESCRIPTIONS
Pin
1
2
Name
Vcc
Output
Function
Supply voltage of gate driver and control circuits.
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 is turned on. To prevent the reversed energy flow, this pin is
disabled once the voltage on IN+ pin is lower than that of IN- pin or the internal one-shot timer is terminated.
The power ground and signal ground. A 0.1µF decoupling capacitor placed between VCC and GND is
recommended.
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 the output
voltage connected directly to VCC pin.
Connecting a diode from this pin to the transformer secondary winding provides on/off information of the primary
switch. Low DET level indicates the secondary rectifier is conducted, therefore the synchronous MOSFET
should be turned on. DET stays high when the primary switch is conducting or secondary rectifier turns off and
the synchronous MOSFET should be turned off.
Current reference. Connecting a resistor from this pin to ground can program the internal current reference I
RT
.
Three internal current sources, which are I
IN+
, I
IN-
, and I
DET
, are then mirrored from I
RT
. I
RT
determines the duration
of the internal one-shot signal, 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, which decreases
the system efficiency. However, if the resistor is too large, the output is shut off immediately once DET gets high.
In SG6203, an internal phase-locked-loop (PLL) modulates the duration of the internal one-shot signal to
maintain a suitable dead time between the primary switch and the synchronous MOSFET.
The inverting input of the current sense comparator. In discontinuous conduction mode, the secondary rectifier
turns 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 is pulled low.
The non-inverting input of the current sense comparator. In discontinuous conduction mode, the secondary
rectifier turns 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 is pulled low.
3
GND
4
VZ
5
DET
6
RT
7
IN-
8
IN+
© System General Corp.
Version 1.0.1 (IAO33.0010.B1)
-2-
www.sg.com.tw • www.fairchildsemi.com
September 24, 2007
Product Specification
Synchronous Rectifier Controller for Flyback Converter
SG6203
BLOCK DIAGRAM
© System General Corp.
Version 1.0.1 (IAO33.0010.B1)
-3-
www.sg.com.tw • www.fairchildsemi.com
September 24, 2007
Product Specification
Synchronous Rectifier Controller for Flyback Converter
SG6203
ABSOLUTE MAXIMUM RATINGS
Symbol
V
CC
I
OUT
V
H
V
L
P
D
Parameter
DC Supply Voltage*
Gate Output Current
DET, OUT, VZ
RT, IN+, IN-
Power Dissipation
SOP8
DIP8
SOP8
DIP8
Value
25
500
-0.3 to 25.0
-0.3 to 7.0
400
800
208.4
82.5
150
-65 to +150
300
2.0
200
Unit
V
mA
V
V
mW
R
θ
JA
T
J
T
STG
T
L
ESD
Thermal Resistance (Junction-to-Air)
Operating Junction Temperature
Storage Temperature Range
Lead Temperature (Soldering, 10 Seconds)
Electrostatic Discharge Capability, Human Body Model
Electrostatic Discharge Capability, Machine Model
°C/W
°C
°C
°C
KV
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
V
CC
T
A
R
T
Parameter
DC Supply Voltage
Operating Ambient Temperature
Pulse Width of the One-shot Signal
Value
<20
-30~85
12~36
Unit
V
°C
KΩ
ELECTRICAL CHARACTERISTICS
V
CC
=12V; R
T=
24KΩ ; T
A=
25°C, unless otherwise noted.
Timing Control Section
Symbol
V
RT
Parameter
Voltage on RT Pin
Test Condition
Min.
1.14
6.5
13
19.5
+40
Typ.
1.20
7.5
15
22.5
+60
Max.
1.26
8.5
17
25.5
+80
Unit
V
µs
µs
µs
%
R
T
=12KΩ
T
RT
Pulse Width of the One-shot Signal
R
T
=24KΩ
R
T
=36KΩ
△
T
RT
Adjustable Range of the Pulse Width
Compared to T
RT
Timing Margin Between Output Turn-off
(Output Falling) and Next Switching Cycle
Start (DET Rising)
R
T
=12KΩ
;
R
T
=24KΩ
;
R
T
=36KΩ
T
DEAD
200
1000
ns
© System General Corp.
Version 1.0.1 (IAO33.0010.B1)
-4-
www.sg.com.tw • www.fairchildsemi.com
September 24, 2007
Product Specification
Synchronous Rectifier Controller for Flyback Converter
SG6203
Min.
1.9
1.2
Synchronous Detection Section
Symbol
V
TH
V
TL
I
DET
T
D
_
LOW
Parameter
Threshold Voltage to Enable One-shot Signal
Threshold Voltage to Enable Output
Current Output from DET Pin
Debounce Time from DET Low to Enable Output
Test Condition
IN+ - IN- > 5mV
R
T
=24KΩ
Typ.
2.1
1.4
250
Max.
2.3
1.6
300
300
Unit
V
V
µA
ns
150
Current Detection Section
Symbol
V
OFFSET
I
IN+
I
IN-
I
IN+
- I
IN-
T
P
PSRR
CMRR
CMRR-f
Parameter
Offset Voltage
Current Output from IN+
Current Output from IN-
Differential Current of IN+ and IN-
Propagation Delay (OUTPUT from Low to High)
Power Supply Rejection Ratio
Common Mode Rejection Ratio
Common Mode Rejection Ratio at 70KHz
Test Condition
R
T
=24KΩ
R
T
=24KΩ
12KΩ < R
T
< 36KΩ
DET< V
TL
, IN+ - IN- > 5mV
Min.
90
90
Typ.
100
100
Max.
10
110
110
1.5
200
Unit
mV
µA
µA
µA
ns
dB
dB
dB
65
65
32
Zener Section
Symbol
V
Z
Parameter
Zener Voltage
Test Condition
I
VZ=
0.1 ~ 3mA
Min.
18
Typ.
19
Max.
20
Unit
V
Output Section
Symbol
V
OH
Parameter
Output Voltage High
Test Condition
V
CC
=12V, I
SOURCE
=50mA
V
CC
=6V, I
SOURCE
=30mA
V
CC
=12V, I
SINK
=50mA
V
CC
=6V, I
SINK
=30mA
T
A
=25°C; C
L
=5nF,
V
CC
=12V
T
A
=25°C; C
L
=5nF,
V
CC
=12V
Min.
11.2
3.5
Typ.
Max.
Unit
V
V
V
OL
Tr
Tf
Output Voltage Low
Rising Time
Falling Time
1
1.2
150
150
175
175
V
V
ns
ns
V
CC
Section
Symbol
V
OP
I
CC_OP
V
TH(ON)
V
TH(OFF)
Parameter
Continuously Operating Voltage
Operating Current
Start Threshold
Minimum Operating Voltage
Test Condition
V
DD
=12V, Output=open,
DET=50KHz,
IN-=IN+=open, R
T
=12KΩ
Min.
Typ.
Max.
20
Unit
V
mA
V
V
1.7
6.0
4.8
5.1
4.0
6.3
© System General Corp.
Version 1.0.1 (IAO33.0010.B1)
-5-
www.sg.com.tw • www.fairchildsemi.com
September 24, 2007
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