?2010 Fairchild Semiconductor Corporation
www.fairchildsemi.com
FAN6920MR " Rev. 1.0.8
5
Pin Definitions (Continued)
Pin #   Name
Description
6
OPFC
otem-pole driver output to drive the external power MOSFET. The clamped gate output voltage is
15.5 V.
7
VDD
Power supply. The threshold voltages for startup and turn-off are 12 V and 7 V, respectively. The
tartup current is less than 30 礎(chǔ) and the operating current is lower than 10 mA.
8
OPWM
otem-pole output generates the PWM signal to drive the external power MOSFET. The clamped
ate output voltage is 17.5 V.
9
GND
he power ground and signal ground.
10
DET
his pin is connected to an auxiliary winding of the PWM transformer through a resistor divider for
he following purposes:
? Producing an offset voltage to compensate the threshold voltage of PWM current limit for over-
power compensation. The offset is generated in accordance with the input voltage when the
PWM switch is on.
? Detecting the valley voltage signal of drain voltage of the PWM switch to achieve the valley
voltage switching and minimize the switching loss on the PWM switch.
? Providing output over-voltage protection. A voltage comparator is built in to the DET pin. The
DET pin detects the flat voltage through a voltage divider paralleled with auxiliary winding. This
flat voltage is reflected to the secondary winding during PWM inductor discharge time. If output
over voltage and this flat voltage are higher than 2.5 V, the controller stops all PFC and PWM
switching operation. The protection mode is auto-recovery.
11
FB
Feedback voltage pin used to receive the output voltage level signal to determine PWM gate duty
or regulating output voltage. The FB pin voltage can also activate open-loop, overload protection
nd output-short circuit protection if the FB pin voltage is higher than a threshold of around 4.2 V
or more than 50 ms. The input impedance of this pin is a 5 k?equivalent resistance. A 1/3
ttenuator is connected between the FB pin and the input of the CSPWM/FB comparator.
12
RT
djustable over-temperature protection and external protection triggering. A constant current flows
ut from the RT pin. When RT pin voltage is lower than 0.8 V (typical), protection is activated and
tops PFC and PWM switching operation. This protection is auto-recovery.
13
VIN
Line-voltage detection for brownin / out protections. This pin can receive the AC input voltage level
hrough a voltage divider. The voltage level of the VIN pin is not only used to control RANGE pins
tatus, but it can also perform brownin / out protection for AC input voltage UVP.
14
ZCD
ero-current detection for the PFC stage. This pin is connected to an auxiliary winding coupled to
PFC inductor winding to detect the ZCD voltage signal once the PFC inductor current discharges
o zero. When the ZCD voltage signal is detected, the controller starts a new PFC switching cycle.
hen the ZCD pin voltage is pulled to under 0.2 V (typical), it disables the PFC stage and the
ontroller stops PFC switching. This can be realized with an external circuit if disabling the PFC
tage is desired.
15
NC
No connection
16
HV
High-voltage startup pin is connected to the AC line voltage through a resistor (100 k?typical) for
providing a high charging current to V
DD
capacitor.