FAN6791

The highly integrated FAN6791/3 dual PWM combinationcontroller provides several features to enhance theperformance of converters.

To minimize standby power consumption, a proprietarygreen-mode function provides off-time modulation tolinearly decrease the switching frequency at light-loadconditions. To avoid acoustic-noise problems, theminimum PWM frequency is set above 20KHz. Thisgreen-mode function enables the power supply to meetinternational power conservation requirements. With theinternal high-voltage startup circuitry, the power lossdue to bleeding resistors is also eliminated. To furtherreduce power consumption, FAN6791/3 is manufacturedusing the CMOS process, which allows an operatingcurrent of only 6mA.

FAN6791/3 integrates a frequency-jittering functioninternally to reduce EMI emissions of a power supplywith minimum line filters. The built-in synchronized slopecompensation achieves stable peak-current-modecontrol. The proprietary internal line compensationensures constant output power limit.

FAN6791/3 provides many protection functions, includingbrownout protection, cycle-by-cycle current limiting, andan internal open-loop protection circuit to ensure safetyshould an open-loop or output short-circuit failure occur.PWM output is disabled until V_DD drops below the UVLOlower limit when the controller restarts. As long as V_DDexceeds ~24.5V, the internal OVP circuit is triggered.