SG6905 Fairchild Semiconductor, SG6905 Datasheet - Page 18

• Manufacturer Part Number: SG6905
• Manufacturer: Fairchild Semiconductor

Green mode PFC/Flyback-PWM Controller
Limited Power Control
Every time when the output of power supply is shorted or
over loaded, the FBPWM voltage will increase. If the
FBPWM voltage is higher than a designed threshold,
FB
OPWM will then be turned off. As OPWM is turned off,
the supply voltage VDD will also begin decreasing.
When V
(10V), SG6905 will be totally shut down. Due to the start
up resistor, V
threshold voltage, V
again. If the over loading condition still exists, the
protection will take place repeatedly. This will prevent the
power supply from being overheated under over loading
condition.
Over-Temperature Protection (OTP)
SG6905 provides an OTP pin for over-temperature
protection. A constant current is output from this pin. If RI
is equal to 24KΩ, then the magnitude of the constant
current will be 100µA. An external NTC thermistor must
be connected from this pin to ground shown as Figure 8.
When the OTP voltage drops below V
SG6905 will be disabled, and will not recovery until OTP
voltage exceeds V
© System General Corp.
Version 1.1.1 (IAO33.0060.B1)
OPEN-LOOP
Fig. 8 OTP function
DD
is lower than the turn-off threshold, V
(4.5V), for longer than t
DD
OTP-ON
will be charged up to the turn-on
DD-ON
(1.4V).
(16V), until SG6905 is enabled
OPEN-PWM
OTP-OFF
(56ms), the
(1.2V),
DD-OFF
- 18 -
Soft-Start
During startup of PWM stage, the SS pin will charge an
external capacitor with a constant current source. The
voltage on FBPWM will be clamped by SS voltage during
startup. In the event of a protected condition occurring
and/or PWM being disabled, the SS pin will be quickly
discharged.
Gate Drivers
SG6905 output stage is a fast totem-pole gate driver. The
output driver is clamped by an internal 18V Zener diode
to protect the external power MOSFET.
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Product Specification
September 27, 2007
SG6905