SG6203 Fairchild Semiconductor, SG6203 Datasheet - Page 2

• Manufacturer Part Number: SG6203
• Description: Synchronous Rectifier Controller
• Manufacturer: Fairchild Semiconductor

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Synchronous Rectifier Controller for Flyback Converter
MARKING DIAGRAMS
ORDERING INFORMATION
Part Number
SG6203SZ
SG6203DZ
PIN DESCRIPTIONS
Pin
1
2
3
4
5
6
7
8
© System General Corp.
Version 1.0.1 (IAO33.0010.B1)
XXXXXXXXYWWV
SG6203TP
Name
Vcc
Output
GND
VZ
DET
RT
IN-
IN+
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
Three internal current sources, which are I
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.
Pb-Free
T: D=DIP, S=SOP
P :
XXXXXXXX: Wafer Lot
Y: Year; WW: Week
V: Assembly Location
Compatible
Z=Lead Free + ROHS
Package
8-Pin SOP
8-Pin DIP
IN+
, I
- 2 -
IN-
, and I
DET
Output
V
GND
, are then mirrored from I
PIN CONFIGURATION
VZ
CC
www.sg.com.tw • www.fairchildsemi.com
RT
Product Specification
. I
RT
determines the duration
September 24, 2007
IN+
IN-
DET
RT
SG6203
RT
.