Green Current-Mode PWM Controller# Technical Documentation: FAN7602BMX Green-Mode PWM Controller
Manufacturer : FAIRCHILD Semiconductor (Note: "FAICHIL" appears to be a typographical error; the correct manufacturer is Fairchild Semiconductor, now part of ON Semiconductor. The component code FAN7602 is a Fairchild part number.)
## 1. Application Scenarios
### Typical Use Cases
The FAN7602BMX is a current-mode PWM (Pulse Width Modulation) controller IC designed primarily for offline switch-mode power supplies (SMPS). Its integrated green-mode function makes it particularly suitable for applications requiring high efficiency at both full and light loads.
Primary Applications Include:
* AC/DC Power Adapters and Chargers: For consumer electronics such as laptops, monitors, printers, and set-top boxes.
* Open-Frame Switching Power Supplies: Used in industrial control systems, telecommunications equipment, and appliance power modules.
* Auxiliary Power Supplies (Standby Rails): Within larger systems like servers, PCs, and televisions, where efficient low-power operation is critical.
* LED Driver Power Supplies: For constant-voltage LED lighting applications, leveraging its precise control and protection features.
### Industry Applications
* Consumer Electronics: Powers devices where energy efficiency standards (like ENERGY STAR, EU CoC) and low no-load power consumption are mandated.
* Industrial Automation: Provides reliable power for control logic, sensors, and communication modules in harsh environments, benefiting from its built-in protections.
* Telecommunications: Used in power modules for network equipment, requiring stable and efficient power conversion.
* Lighting Industry: Serves as the core controller for efficient LED driver power stages.
### Practical Advantages and Limitations
Advantages:
* High Efficiency Across Load Range: The proprietary green-mode function provides burst-mode operation at light loads, significantly reducing switching losses and lowering standby power consumption (often to <100mW).
* Reduced EMI: Variable frequency operation in green mode and a built-in frequency jitter function help spread EMI spectrum, simplifying filter design and compliance.
* Robust Protection Suite: Integrates Over-Current Protection (OCP), Over-Voltage Protection (OVP), Over-Load Protection (OLP), and Internal Thermal Shutdown (TSD), enhancing system reliability.
* Low Startup Current: Typically <20µA, allowing the use of a high-value startup resistor, which reduces power loss in the startup circuit.
* Cycle-by-Cycle Current Limiting: Provides fast response to output overloads and short circuits, protecting the power MOSFET and secondary components.
Limitations:
* Fixed Peak Current Limit: The OCP threshold is internally set, requiring careful selection of the current-sense resistor (`Rcs`) and power MOSFET to match the desired maximum output power. It lacks user-programmability for this key parameter.
* Frequency Variation: The switching frequency decreases in green mode. While this improves light-load efficiency, it requires the transformer and output filter to be designed to handle a wider frequency range without audible noise or performance degradation.
* Discontinuous Conduction Mode (DCM) Focus: Optimized for DCM/flyback topology operation. For continuous conduction mode (CCM) designs, loop compensation requires extra care due to a right-half-plane zero.
* Limited Maximum Duty Cycle: The internal maximum duty cycle clamp (typically ~72%) must be considered during transformer design to ensure sufficient volt-second product for the required output voltage.
## 2. Design Considerations
### Common Design Pitfalls and Solutions
1. Pitfall: Audible Noise in Green Mode.
* Cause: The controller entering burst mode at very light loads can cause the transformer or ceramic capacitors to vibrate at audible frequencies.
* Solution: Ensure
