FAN6921MLMY Fairchild Semiconductor, FAN6921MLMY Datasheet - Page 17

• Manufacturer Part Number: FAN6921MLMY
• Description: TAPE REEL \ Integrated PFC And Flyback Controller
• Manufacturer: Fairchild Semiconductor

Specifications of FAN6921MLMY

• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

© 2010 Fairchild Semiconductor Corporation
FAN6921ML • Rev. 1.0.1
PFC Peak Current Limiting (CSPFC pin)
During PFC stage switching operation, the PFC switch
current is detected by a current-sense resistor on the
CSPFC pin and the detected voltage on this resistor is
delivered to an input terminal of a comparator and
compared with a threshold voltage 0.6V (typical). Once
the CSPFC pin voltage is higher than the threshold
voltage, 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.
Brownin/out Protection (VIN Pin)
With AC voltage detection, FAN6921ML can perform
brownin/out protection (AC voltage UVP). Figure 34
shows the key operation waveforms. The VIN pin is
used to detect AC input voltage level and is connected
to AC input by a resistor divider (refer to Figure 1);
therefore, the V
input voltage. When the AC voltage drops; and V
voltage is lower 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 voltage
is lower than 1.2V, FAN6921ML stops all PFC and
PWM switching operation immediately until V
voltage drops to turn-off voltage then rises to turn-on
voltage again (UVLO).
When the brownout protection is activated, all switching
operation is turned off, the V
mode up and down continuously. Until V
higher than 1.2V (typical) and V
voltage again, the PWM and PFC gate is sent out.
The measured waveforms of brownin/out protection are
shown in Figure 35.
CSPFC
OPFC
Figure 33. Cycle-by-Cycle Current Limiting
VIN
voltage is proportional to the AC
PFC MOS Current Limit
DD
voltage enters hiccup
DD
reaches turn-on
VIN
voltage is
VIN
DD
AC Input
17
AC Input
Figure 34. Operation Waveforms of Brownin/out
Brownout
Figure 35. Measured Waveform of Brownin/out
V
DD
OPWM
Protection (Adapter Application)
OPFC
V
DD
Hiccup Mode
Protection
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Brownin