sg6901asz-f116 Fairchild Semiconductor, sg6901asz-f116 Datasheet - Page 13

• Manufacturer Part Number: sg6901asz-f116
• Description: Pfc/flyback-pwm Controller
• Manufacturer: Fairchild Semiconductor

SG6901A is a highly integrated PFC/PWM combination
controller. Many functions and protections are built in to
provide a compact design. The following sections
describe the operation and function.
Switching Frequency and Current
Sources
The
programmed by the resistor R
and GND. The relationship is:
For example, a 24KΩ resistor R
switching frequency. Accordingly, a constant current, I
flows through R
I
Line Voltage Detection (VRMS)
Figure 1 shows a resistive divider with low-pass filtering
for line-voltage detection on the VRMS pin. The V
voltage is used for the PFC multiplier, brownout
protection, and range control.
For brownout protection, the SG6901A is disabled with
195ms delay time if the voltage V
For PFC multiplier and range control, refer to section
below for more details.
PFC / Flyback PWM Controller
OPERATION DESCRIPTION
© System General Corp.
Version 1.0.1 (IAO33.0062.B0)
F
I
T
T
OSC
is used to generate internal current reference.
=
R
=
switching
1.2V
I
R
(kΩ
FIG.1 Line Voltage Detection Circuit
1560
I
(kΩ
)
(mA)
I
:
)
frequency
(kHz)
----------------
-----------
I
connected between RI pin
of
RMS
I
SG6901A
results in a 65KHz
drops below 0.8V.
can
(1)
(2)
RMS
be
T
- 13 -
,
PFC Output Voltage Control (RANGE)
For an universal input (90 ~ 264V
applying active boost PFC and flyback as a second stage,
the output voltage of PFC is usually designed around
250V at low line and 390V at high line. This can improve
the efficiency at low-line input. The RANGE pin
(open-drain structure) is used for the two-level output
voltage setting.
Figure 2 shows the RANGE output that programs the PFC
output voltage. The RANGE output is shorted to ground
when the V
of high impedance (open) whenever the V
drops below V
designed using equations:
Range
Range
FIG.2 Range Control Two-Level Output Voltage
=
=
Open
Ground
RMS
⇒
www.sg.com.tw • www.fairchildsemi.com
⇒
V
RMS-L
voltage exceeds V
O
V
O
=
=
R
A
R
(1.6V). The output voltages can be
R
A
+
B
(
R
R
+
B
B
(
R
//
×
B
R
3
//
V
C
R
)
C
Product Specification
)
RMS-H
×
3
V
September 26, 2007
----
AC
(1.95V) while it is
) power supply
RMS
SG6901A
voltage
(3)