SG6903SZ Fairchild Semiconductor, SG6903SZ Datasheet - Page 13

IC PFC CONTROLLER 16SOIC

SG6903SZ

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

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
SG6903 is a highly integrated PFC/PWM combo
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
Figure 1 shows the start-up circuit of the SG6903. A
resistor R
is utilized to charge V
capacitor through S1.
AC
DD
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
DD
can be delivered from auxiliary winding of the main
transformer. V
must not drop below 10V during this
DD
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
can be large to reduce power
AC
consumption. One 10µF capacitor should hold enough
energy for successful start-up. After start-up, S1 will
switch so that the current I
will be the input for PFC
AC
multiplier. This helps reduce circuit complexity and
power consumption.
FIG.1 Start-up circuit of the SG6903
© System General Corp.
Version 1.0.1 (IAO33.0061.B0)
Switching Frequency and Current
Sources
The switching frequency of SG6903 can be
programmed by the resistor R
and GND. The relationship is:
=
F
OSC
For example, a 24KΩ resistor R
switching frequency. Accordingly, a constant Current I
will flow through R
before the energy
=
I
T
R
I
I
is used to generate internal current reference.
T
during
DD
Line Voltage Detection (VRMS)
Figure 2 shows a resistive divider with low-pass
filtering for line-voltage detection on VRMS pin. The
V
voltage is used for the PFC multiplier, brownout
RMS
protection, and range control.
For brownout protection, the SG6903 is disabled
with 195ms delay time if the voltage V
0.8V.
For PFC multiplier and range control, please refer
to below section for more details.
FIG.2 Line voltage detection circuit
- 13 -
Product Specification
SG6903
connected between RI pin
I
1560
(KHz)
----------- (1)
R
(kΩ
)
I
results in a 65 KHz
I
.
I
1.2V
(mA)
---------------- (2)
(kΩ
)
drops below
RMS
www.sg.com.tw • www.fairchildsemi.com
September 28, 2007
T

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