FAN6749: Green-Mode PWM Controller for Flyback Converter, 65KHz, 2 level OCP

The FAN6749 highly integrated PWM controller enhances the performance of flyback converters. To minimize standby power consumption, a proprietary Green-Mode function continuously decreases the switching frequency under light-load conditions. Under zero-load conditions, the power supply enters Burst Mode and completely shuts off PWM output. Green Mode helps power supplies meet international power conservation requirements.

The FAN6749 is designed for SMPS with surge-current output and incorporates a two-level Over-Current Protection (OCP) function. Besides the cycle-by-cycle current limiting, two-level OCP can handle peak loading within a specified delay time.

FAN6749 also integrates a frequency-hopping function that helps reduce EMI emission of a power supply with minimum line filters. Built-in synchronized slope compensation helps achieve stable peak-current control. To keep constant output power limit over universal AC input range, the current limit and OCP threshold voltage are adjusted according to AC line voltage detected by the HV pin. Gate output is clamped at 14.5V to protect the external MOSFET from over-voltage damage.

Other protection functions include: AC input brownout protection with hysteresis, Short-Circuit Protection (SCP) for output-short condition, and VDD Over-Voltage Protection (OVP). For over-temperature protection, an external NTC thermistor can be applied to sense the ambient temperature. When OLP, OCP, SCP, VDD OVP, or OTP is activated, an internal latch circuit latches off the controller. The latch resets when VDD is removed.

There are three differences from FAN6748 to FAN6749:

Features

• High-Voltage Startup
• Low Operating Current: 1.8mA
• Linearly Decreasing PWM Frequency to 24kHz
• Proprietary Frequency Hopping to Reduce EMI
• Two-Level Over-Current Protection (OCP), 1400ms Delay for Normal Peak Load
• Two-Level OCP, 56ms Delay for Super Peak Load
• Output Short-Circuit Protection (SCP)
• Peak-Current Mode Operation with Cycle-by-Cycle Current Limiting
• HV Pin Brown-in/out Protection with Hysteresis
• Constant Power Limit by HV Sampling
• Internal FB Open-Loop Protection (OLP)
• GATE Output Maximum Voltage Clamp: 14.5V
• V_DD Over-Voltage Protection (OVP)
• Programmable Over-Temperature Protection (OTP)
• Integrated 6ms Soft-Start Function
• Internal Latch Circuit (OVP, OTP, OCP, OLP, SCP)
• Internal OTP Sensor with Hysteresis