This application note describes step-by-step design considerations for a power supply using the FAN480X controller. The FAN480X combines a PFC controller and a PWM controller. The PFC controller employs average current mode control for Continuous Conduction Mode (CCM) boost converter in the front end. The PWM controller can be used in either current mode or voltage mode for the downstream converter. In voltage mode, feed-forward from the PFC output bus can be used to improve the line transient response of PWM stage. In either mode, the PWM stage uses conventional trailing-edge duty cycle modulation, while the PFC uses leading-edge modulation. This proprietary leading/trailing-edge modulation technique can significantly reduce the ripple current of the PFC output capacitor. The synchronization of the PWM with the PFC simplifies the PWM compensation due to the controlled ripple on the PFC output capacitor (the PWM input capacitor). In addition to power factor correction, a number of protection features have been built in to the FAN480X. These include programmable soft-start, PFC over-voltage protection, pulse-by-pulse current limiting, brownout protection, and under-voltage lockout. FAN4801/2/2L feature programmable two-level PFC output to improve efficiency.
The document describes step-by-step design considerations for a power supply utilizing the FAN480X controller, which combines a PFC controller employing average current mode control with a PWM controller. The note details the functional description of the Gain Modulator, Current and Voltage Control loops, Brownout Protection, Two-Level PFC Output, Oscillator configuration, and PWM stage operation.
| PFC Controller Type | Average current mode control for CCM boost converter |
|---|---|
| PWM Control Modes | Current mode or voltage mode |
| Brownout Protection Trip Point (VRMS) | 1.05V (0.9V for FAN4802L) |
| Brownout Protection Restart Point (VRMS) | 1.9V (1.65V for FAN4802L) |
| PWM Comparator Offset Voltage | 1.5V |
| Vry OK Comparator Threshold | 2.4V |
The series includes FAN4800A, FAN4800C, FAN4801, FAN4802, and FAN4802L.
The synchronization simplifies PWM compensation due to controlled ripple on the PFC output capacitor.
Features include programmable soft-start, PFC over-voltage protection, pulse-by-pulse current limiting, brownout protection, and under-voltage lockout.