Green Current-Mode PWM Controller# Technical Documentation: FAN7602BN PWM Controller IC
## 1. Application Scenarios
### 1.1 Typical Use Cases
The FAN7602BN is a high-performance, current-mode PWM controller IC designed primarily for offline switch-mode power supplies (SMPS) . Its architecture is optimized for flyback converter topologies , making it a core component in AC-DC power conversion systems requiring precise regulation and high efficiency.
Primary Applications Include:
* Standby Power Supplies: Provides stable, low-power output for electronic devices in standby or sleep modes, commonly found in televisions, monitors, and home appliances.
* Adapter/Charger Circuits: Forms the control heart of external power adapters for laptops, printers, and consumer electronics, offering compact design and good line/load regulation.
* Auxiliary Power Supplies: Used to generate lower-voltage rails (e.g., 5VSB, 12V) from a high-voltage DC bus within larger power systems like desktop PC power supplies or industrial equipment.
### 1.2 Industry Applications
* Consumer Electronics: Integral to the power subsystems of TVs, set-top boxes, audio systems, and gaming consoles due to its cost-effectiveness and reliability.
* Computer & Peripherals: Employed in PC main power supplies for the standby rail and in monitors, printers, and external storage devices.
* Industrial Controls: Used in control panels, sensor modules, and embedded systems where a robust, isolated low-power supply is required from an AC mains input.
* Lighting: Found in LED driver circuits for commercial and residential lighting that require AC-DC conversion with dimming or constant-current capabilities.
### 1.3 Practical Advantages and Limitations
Advantages:
* High Integration: Incorporates a high-voltage startup circuit, oscillator, error amplifier, current sensing comparator, and gate driver, reducing external component count.
* Low Startup Current: Features a very low startup current (typically <30 µA), enabling quick and reliable startup from the high-voltage DC link with minimal power dissipation in the startup resistor.
* Advanced Protection Features: Built-in protections include Overload Protection (OLP), Over-Voltage Protection (OVP), and Internal Thermal Shutdown (TSD) , enhancing system reliability.
* Frequency Jittering: The oscillator incorporates frequency jittering to reduce peak EMI emissions, simplifying filter design and compliance with electromagnetic compatibility (EMC) standards.
* Green Mode Operation: Includes a proprietary green mode function that reduces switching frequency under light-load conditions, significantly improving system efficiency at low output power.
Limitations:
* Topology Constraint: Primarily optimized for flyback converters. For forward, half-bridge, or LLC topologies, alternative controllers may be more suitable.
* Power Range: Best suited for low-to-medium power applications (typically up to 30-50W). For higher power levels, its internal MOSFET driver may require an external booster stage.
* Fixed Internal Parameters: Features like maximum duty cycle and oscillator frequency range are fixed, offering less design flexibility compared to fully programmable digital controllers.
## 2. Design Considerations
### 2.1 Common Design Pitfalls and Solutions
* Pitfall 1: Inadequate VDD Capacitor Selection.
* Issue: An undersized capacitor at the VDD pin can cause the voltage to dip below the UVLO threshold during startup or heavy transient loads, leading to erratic operation or shutdown.
* Solution: Calculate the VDD capacitor value based on the IC's startup current, startup time, and the current supplied by the auxiliary winding. A typical value ranges from 10µF to 47µF. Ensure it is a low-ESR type and placed close to the IC.
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