SG6902 Fairchild Semiconductor, SG6902 Datasheet - Page 18

• Manufacturer Part Number: SG6902
• Description: Green-Mode PFC / Flyback-PWM Controller
• Manufacturer: Fairchild Semiconductor

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Green-Mode PFC / Flyback-PWM Controller
and the output power limit is higher than under low V
To compensate for this variation, the peak current
threshold is modulated by the RANGE output. When
RANGE is shorted to GND, the PFC output voltage is
high and the corresponding threshold is 0.65V. When
RANGE is opened, the PFC output voltage is low and the
corresponding threshold is 0.7V.
FIG.8 Peak Current Control Loop
Limited Power Control
Every time the output of power supply is shorted or
overloaded, the FBPWM voltage increases. If the FB
voltage is higher than a designed threshold, 4.5V, for
longer than 56ms, the OPWM is turned off.
turned off, the supply voltage V
When V
10V, SG6902 is totally shut down. Due to the start-up
resistor, V
voltage, 16V, until enabled again. If the overloading
condition persists, the protection occurs repeatedly to
prevent the power supply from being overheated during
overloading
© System General Corp.
Version 1.3.1 (IAO33.0022.B3)
DD
DD
is lower than the turn-off threshold, such as
condition.
is charged up to the turn-on threshold
DD
begins decreasing.
As OPWM is
PFC
- 18 -
.
Over-Temperature Protection (OTP)
SG6902 provides an OTP pin for over-temperature
protection. A constant current is output from this pin. If R
is equal to 24kΩ, the magnitude of the constant current is
100µA. An external NTC thermistor must be connected
from this pin to ground, as shown as Figure 9. When the
OTP voltage drops below 1.2V, SG6902 is disabled until
the OTP voltage exceeds 1.4V.
Fig.9 OTP Function
Soft-Start
During start-up of PWM stage, the SS pin charges an
external capacitor with a constant current source. The
voltage on FBPWM is clamped by SS voltage during
start-up. In the event of a protection condition and/or
PWM being disabled, the SS pin quickly discharges.
Gate Drivers
SG6902 output stage is a fast totem-pole gate driver. The
output driver is clamped by an internal 18V Zener diode
to protect the power MOSFET.
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Product Specification
September, 2007
SG6902
I