FAN6920MR Fairchild Semiconductor, FAN6920MR Datasheet - Page 18

• Manufacturer Part Number: FAN6920MR
• Description: The highly integrated FAN6920MR combines Power Factor Correction (PFC) controller and quasi-resonant PWM controller
• Manufacturer: Fairchild Semiconductor

© 2010 Fairchild Semiconductor Corporation
FAN6920MR • Rev. 1.0.5
PFC Peak Current Limiting (CSPFC Pin)
During PFC stage switching operation, the PFC switch
current is detected by the current-sense resistor on the
CSPFC pin and the detected voltage on this resistor is
delivered to the input terminal of a comparator and
compared with a threshold voltage 0.82V (typical). Once
the CSPFC pin voltage is higher than the threshold
voltage, the PFC gate is turned off immediately.
The PFC peak switching current is adjustable by the
current-sense resistor. Figure 33 shows the measured
waveform of PFC gate and CSPFC pin voltage.
Brownout / In Protection (VIN Pin)
With AC voltage detection, FAN6920MR can perform
brownout / in protection (AC voltage UVP). Figure 34
shows the key operation waveforms of brownout / in
protection. Both use the VIN pin to detect AC input
voltage level and the VIN pin is connected to AC input
by a resistor divider (refer to Figure 1); therefore, the
V
When the AC voltage drops and V
than 1V for 100ms, the UVP protection is activated and
the COMP pin voltage is clamped to around 1.6V.
Because PFC gate duty is determined by comparing the
sawtooth waveform and COMP pin voltage, lower
COMP voltage results in narrow PFC on-time, so that
the energy converged is limited and the PFC output
voltage decreases. When INV pin is lower than 1.2V,
FAN6920MR stops all PFC and PWM switching
operation immediately until V
voltage then rises to turn-on voltage again (UVLO).
When the brownout protection is activated, all switching
operation is turned off and, V
mode up and down continuously. Until V
higher than 1.3V (typical) and V
voltage again, the PWM and PFC gate is sent.
The measured waveforms of brownout / in protection
are shown in Figure 35.
VIN
CSPFC
OPFC
Figure 33. Cycle-by-Cycle Current Limiting
voltage is proportional to the AC input voltage.
PFC MOS Current Limit
DD
DD
voltage drops to turn-off
voltage enters hiccup
DD
VIN
reaches turn-on
voltage is lower
0.82V
VIN
voltage is
18
AC Input
Brownout
Figure 35. Measured Waveform of Brownout / In
Figure 34. Operation Waveforms of Brownout /
V
DD
Protection (Adapter Application)
OPWM
OPFC
V
DD
Hiccup Mode
In Protection
Brown-In
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