Highly Integrated Green-Mode PWM Controller Brownout and VLimit Adjustment by HV Pin # Technical Documentation: FAN6754WAMRMY PWM Controller
Manufacturer : FAIRCHILD (now part of ON Semiconductor)
Component Type : Quasi-Resonant PWM Controller IC for Switch-Mode Power Supplies (SMPS)
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## 1. Application Scenarios
### Typical Use Cases
The FAN6754WAMRMY is a highly integrated pulse-width modulation (PWM) controller designed for offline power supplies operating in quasi-resonant (QR) mode. Its primary function is to regulate output voltage in AC-DC converters by controlling the switching of a power MOSFET.
Primary Applications Include:
- Standby Power Supplies : For appliances, gaming consoles, and set-top boxes requiring low no-load power consumption.
- Adapter/Charger Circuits : Used in laptop adapters, mobile device chargers, and USB-PD power sources where high efficiency across loads is critical.
- Auxiliary Power Supplies : In servers, telecom systems, and industrial equipment to provide low-power bias rails.
- LED Driver Power Stages : For constant-voltage LED drivers requiring precise regulation and dimming compatibility.
### Industry Applications
- Consumer Electronics : TVs, monitors, audio equipment leveraging its low standby power (<100mW typical) to meet energy standards like ENERGY STAR and EU CoC Tier 2.
- Computing & Peripherals : PC power supplies (standby rail), printers, and external storage devices.
- Industrial Automation : Control panel power modules, sensor interfaces requiring robust, isolated power.
- Networking Equipment : Routers, switches, and modems where compact size and reliability are key.
### Practical Advantages
- High Efficiency : Quasi-resonant operation reduces switching losses by turning on the MOSFET at valley voltage, improving efficiency, especially at light loads.
- Low Standby Power : Integrated burst-mode operation minimizes switching frequency under light/no-load conditions, reducing power consumption.
- Comprehensive Protection : Includes over-voltage protection (OVP), over-load protection (OLP), over-temperature protection (OTP), and latch-off for fault conditions.
- Minimal External Components : Internal high-voltage startup circuit eliminates need for external startup resistor, saving board space and cost.
- Frequency Jittering : Reduces EMI peak emissions, easing compliance with CISPR22/FCC Class B.
### Limitations
- Limited Maximum Power : Best suited for designs up to 75W due to QR operation constraints; for higher power, continuous conduction mode (CCM) controllers may be preferable.
- Line/Load Transient Response : QR mode can exhibit slower transient response compared to fixed-frequency PWM; may require careful loop compensation.
- Minimum Load Requirements : May need a minimum load to maintain regulation in burst mode, which can be a constraint for some applications.
- Complex Magnetics Design : Quasi-resonant operation requires transformer design with controlled leakage inductance for valley switching, increasing design complexity.
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## 2. Design Considerations
### Common Design Pitfalls and Solutions
- Insufficient VDD Capacitance : Causes controller reset during startup.
*Solution*: Use a VDD capacitor ≥22µF (low-ESR electrolytic or ceramic) placed close to VDD and GND pins.
- Unstable Operation at Light Loads : Can cause audible noise or output ripple.
*Solution*: Adjust burst-mode thresholds via feedback network; ensure transformer core material avoids magnetostriction.
- Over-Voltage Protection Nuisance Triggering : Due to noise on OVP pin.
*Solution*: Add a small RC filter (e.g., 1kΩ, 100pF) at OVP sense pin; keep trace short.
- Poor EMI Performance : Despite frequency jittering.
*Solution*: Ensure proper grounding, use Y-capacitors, and add a
