SG6903SZ Fairchild Semiconductor, SG6903SZ Datasheet - Page 13

• Manufacturer Part Number: SG6903SZ
• Description: IC PFC CONTROLLER 16SOIC
• Manufacturer: Fairchild Semiconductor

Specifications of SG6903SZ

• Mounting Type: Surface Mount
• Package / Case: 16-SOIC (3.9mm Width)
• Output Voltage: 1.5 V to 8 V
• Switching Frequency: 65 KHz
• Operating Temperature Range: - 20 C to + 85 C
• Mounting Style: SMD/SMT
• Duty Cycle (max): 83 %
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Voltage - Supply: -
• Operating Temperature: -
• Frequency - Switching: -
• Mode: -
• Current - Startup: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

Green Mode PFC/Flyback-PWM Controller
OPERATION DESCRIPTION
controller. Lots functions and protections are built in to
provide a possible compact design. The following
description will describe the operation and function in
detail to give an overview of this chip.
Start-up
resistor R
The turn-on and turn-off threshold of SG6903 are fixed
internally at 16V/10V. During start-up, the hold-up
capacitor must be charged to 16V through the start-up
resistor so that SG6903 will be enabled. The hold-up
capacitor will continue to supply V
can be delivered from auxiliary winding of the main
transformer. V
start-up process. This UVLO hysteresis window ensures
that hold-up capacitor is adequate to supply V
start-up. Since SG6903 consumes less than 25µA startup
current, the value of R
consumption. One 10µF capacitor should hold enough
energy for successful start-up. After start-up, S1 will
switch so that the current I
multiplier. This helps reduce circuit complexity and
power consumption.
© System General Corp.
Version 1.0.1 (IAO33.0061.B0)
SG6903 is a highly integrated PFC/PWM combo
Figure 1 shows the start-up circuit of the SG6903. A
AC
FIG.1 Start-up circuit of the SG6903
is utilized to charge V
DD
must not drop below 10V during this
AC
can be large to reduce power
AC
will be the input for PFC
DD
DD
capacitor through S1.
before the energy
DD
during
- 13 -
Switching Frequency and Current
Sources
programmed by the resistor R
and GND. The relationship is:
switching frequency. Accordingly, a constant Current I
will flow through R
Line Voltage Detection (VRMS)
filtering for line-voltage detection on VRMS pin. The
V
protection, and range control.
with 195ms delay time if the voltage V
0.8V.
to below section for more details.
RMS
The switching frequency of SG6903 can be
For example, a 24KΩ resistor R
I
Figure 2 shows a resistive divider with low-pass
For brownout protection, the SG6903 is disabled
For PFC multiplier and range control, please refer
voltage is used for the PFC multiplier, brownout
F
I
T
T
OSC
is used to generate internal current reference.
=
FIG.2 Line voltage detection circuit
=
R
I
1.2V
www.sg.com.tw • www.fairchildsemi.com
R
(kΩ
1560
I
(kΩ
I
.
)
(mA)
)
(KHz)
---------------- (2)
I
connected between RI pin
Product Specification
----------- (1)
September 28, 2007
I
results in a 65 KHz
RMS
drops below
SG6903
T