FAN6791 Datasheet, PDF (5/19 Pages) Fairchild Semiconductor – Highly Integrated, Dual-PWM Combination Controller

Pin Definitions
Pin # Name Description
1
HV For startup, this pin is pulled HIGH to the line input or bulk capacitor via resistors.
2
NC No connection.
3
GND Ground.
Oscillator Setting. One resistor connected between RI and ground pins determines the switching
4
RI
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.
5
FBFYB
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.
6
IFYB
PWM Current Sense for Flyback PWM Stage. The sensed voltage is used for peak-current-
mode control and cycle-by-cycle current limiting.
7
FBPWM
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.
8
IPWM
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.
9 VREF 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
10
SS 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.
11
ON/OFF
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.
12 PGND Ground. The power ground.
13
OPWM
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.
14
VDD
Power Supply. The internal protection circuit disables PWM output as long as VDD exceeds the
OVP trigger point.
15
OFYB
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.
16
VRMS
Line-Voltage Detection. The pin is used for line compensation, for forward, and brownout
protection.
© 2008 Fairchild Semiconductor Corporation
FAN6791 / FAN6793 • Rev. 1.0.2
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