FAN6791 Fairchild Semiconductor, FAN6791 Datasheet - Page 6

• Manufacturer Part Number: FAN6791
• Description: The highly integrated FAN6791/3 dual PWM combination controller provides several features to enhance the performance of converters
• Manufacturer: Fairchild Semiconductor

© 2008 Fairchild Semiconductor Corporation
FAN6791 / FAN6793 • Rev. 1.0.3
Pin Definitions
Pin #
10
11
12
13
14
15
16
1
2
3
4
5
6
7
8
9
FBPWM
ON/OFF
FBFYB
OPWM
Name
PGND
VRMS
IPWM
OFYB
VREF
GND
IFYB
VDD
NC
HV
SS
RI
Description
For startup, this pin is pulled HIGH to the line input or bulk capacitor via resistors.
No connection.
Ground.
Oscillator Setting. One resistor connected between RI and ground pins determines the switching
frequency (resistance between 12 ~ 47kΩ is recommended). The switching frequency is equal to
[1560 / RI]kHz, where RI is in kΩ. For example, if RI is equal to 24kΩ, then the switching frequency
is 65kHz.
Voltage Feedback for Flyback PWM Stage. It is internally pulled HIGH through a 6.5kΩ resistor.
An external opto-coupler from secondary feedback circuit is usually connected to this pin.
PWM Current Sense for Flyback PWM Stage. The sensed voltage is used for peak-current-
mode control and cycle-by-cycle current limiting.
Voltage Feedback for Forward PWM Stage. It is internally pulled HIGH through a 6.5kΩ resistor.
An external opto-coupler from secondary feedback circuit is usually connected to this pin.
PWM Current Sense for Forward PWM Stage. Via a current sense resistor, this pin provides the
control input for peak-current-mode control and cycle-by-cycle current limiting.
Reference Voltage. This pin can provide a reference voltage 5V.
PWM Soft-Start. During startup, the SS pin charges an external capacitor with a 20µA constant
current source. The voltage on FBPWM is clamped by SS during startup. In the event of a
protection condition occurring and/or forward PWM being disabled, the SS pin quickly discharges.
PWM Remote ON/OFF. Active HIGH. The forward PWM is disabled whenever the voltage at this
pin is lower than 0.8V or the pin is open.
Ground. The power ground.
Forward PWM Gate Drive. The totem-pole output drive for the forward PWM MOSFET. This pin is
internally clamped under 16V to protect the MOSFET.
Power Supply. The internal protection circuit disables PWM output as long as V
OVP trigger point.
Flyback PWM Gate Drive. The totem-pole output drive for the forward PWM MOSFET. This pin is
internally clamped under 16V to protect the MOSFET.
Line-Voltage Detection. The pin is used for line compensation, for forward, and brownout
protection.
6
DD
exceeds the
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