FAN6920 Ver la hoja de datos (PDF) - Fairchild Semiconductor

Número de pieza

componentes Descripción

Fabricante

FAN6920

Integrated Critical-Mode PFC and Quasi-Resonant Current-Mode PWM Controller

Fairchild Semiconductor 

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.

PFC MOS Current Limit

0.82V

CSPFC

OPFC

Figure 33. Cycle-by-Cycle Current Limiting

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

VVIN voltage is proportional to the AC input voltage.

When the AC voltage drops and VVIN 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 is lower than 1.2V,

FAN6920MR stops all PFC and PWM switching

operation immediately until VDD 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 and, VDD voltage enters hiccup

mode up and down continuously. Until VVIN voltage is

higher than 1.3V (typical) and VDD reaches turn-on

voltage again, the PWM and PFC gate is sent.

The measured waveforms of brownout / in protection

are shown in Figure 35.

Figure 34. Operation Waveforms of Brownout /

In Protection

VDD

VDD Hiccup Mode

Brownout

AC Input

OPWM

OPFC

Brown-In

Figure 35. Measured Waveform of Brownout / In

Protection (Adapter Application)

© 2010 Fairchild Semiconductor Corporation

FAN6920MR • Rev. 1.0.3

18

www.fairchildsemi.com

Share Link: