LNK364PN Enables High-Efficiency, Energy-Saving Designs for Low-Power Supplies

^{October 9, 2025 — With smart home appliances, IoT devices, and industrial controllers placing increasingly stringent demands on energy efficiency and compact design, highly efficient and streamlined switching power supply chips have become pivotal components in product development. Recently, Shenzhen Anxinruo Technology Co., Ltd., a well-known domestic provider of integrated circuit solutions, officially recommended its widely adopted LinkSwitch-XT2 series product — the LNK364PN. This chip delivers an exceptional implementation solution for various applications with output power up to 10W, thanks to its high integration, outstanding energy efficiency, and robust protection features.}

 

^{I. Chip Introduction: LNK364PN}

 

^{The LNK364PN is a high-performance, offline switching power supply integrated circuit from the LinkSwitch-XT2 series. Featuring an innovative design, this device integrates a 700V power MOSFET, oscillator, on/off control state machine, and comprehensive protection circuits within a single DIP-8C package, delivering an ultra-compact and highly efficient solution for low-power supply designs.}

 

^{Core Features and Advantages:}

^{High Energy Efficiency: Consumes less than 70mW under no-load conditions at 265VAC input, easily meeting stringent global energy efficiency standards.}

 

^{Simplified Design: Highly integrated architecture requires minimal external components. Eliminates the need for optocouplers and secondary feedback circuits while delivering precise constant voltage/current output, significantly reducing system cost and size.}

 

^{High Reliability: Comprehensive built-in protection features including short-circuit, open-loop, over-temperature, and output over-voltage protection, substantially enhancing power supply robustness.}

 

^{Wide Voltage Input: Supports 85VAC to 265AC wide-range input, suitable for global market applications.}

 

II. Description of Typical Application Circuit

 

 

^{Circuit Core Structure and Workflow}

 

^{1.Input Stage and Primary Side}

^{AC Input and Rectification: The AC input is full-wave rectified by the bridge rectifier BR1 and filtered by the bulk electrolytic capacitor C1 to produce high-voltage DC.}

 

^{​LNK364PN Core}

^{Drain: The drain of the internally integrated 700V MOSFET is directly connected to the primary winding of the high-frequency transformer T1. This serves as the "power switching" core of the entire switching power supply.}

 

^{Unique "Clamp-less" Design: Leveraging the internally integrated 700V MOSFET and advanced drain sensing technology of the LNK364PN, this design eliminates the need for the traditional RCD clamp or Zener clamp circuit required in flyback topologies. This not only saves component cost and board space but also improves reliability. The chip can withstand voltage spikes caused by transformer leakage inductance.}

 

^{2.Output Stage and Feedback}

^{Secondary Rectification and Filtering:
When the internal MOSFET turns off, the energy stored in the transformer's secondary winding is rectified by diode D1 and filtered by capacitor C2 to produce a smooth DC output voltage (e.g., +12V).}

 

^{Simplified Feedback Mechanism:
The output voltage is sampled by a voltage divider composed of resistors R1 and R2. This sampled signal directly drives the LED inside a low-cost optocoupler (e.g., PC817), thereby transmitting the output-side voltage information across the isolation barrier to the primary side.}

 

^{3.Feedback and Control Loop}

^{The transistor side of the optocoupler is connected to the feedback pin (FB) of the LNK364PN.}

^{Based on this feedback signal, the chip regulates the turn-on and turn-off times of the power switch through its on/off control mode, thereby precisely stabilizing the output voltage and achieving constant voltage (CV) output.}

 

^{Core Advantages in Design}

^{Extreme Simplicity: The highly integrated monolithic IC design, combined with the clamp-less architecture, minimizes the number of external components required.}

 

_{Cost Efficiency: Eliminates the need for clamp circuits and secondary precision voltage references (such as TL431), resulting in a highly competitive system BOM cost.}

 

_{High Reliability: The built-in auto-restart function disables output and initiates retry attempts during short-circuit or open-loop fault conditions, protecting both the chip and the load. Over-temperature protection further ensures system safety under abnormal conditions.}

 

^{Effortless Compliance with Energy Efficiency Standards: EcoSmart® technology guarantees extremely low no-load power consumption (<70 mW), easily meeting global energy efficiency regulations.}

 

^{III. Detailed Explanation of Internal Functional Modules} 

 

 

 

 

^{Core Architecture:
The LNK364PN employs an intelligent power integration architecture comprising three core modules: the power MOSFET, control logic, and protection circuitry.}

 

^{Key Functional Modules:}

 

^{1.5.8V Precision Regulator}

^{Provides stable operating voltage for internal circuitry}

^{Incorporates 4.8V undervoltage lockout (UVLO) protection}

 

^{2.Intelligent Control Core}

^{Auto-Restart Counter: Periodically attempts recovery during fault conditions}

^{Clock Oscillator: Integrated frequency jittering technology optimizes EMI performance}

^{Leading Edge Blanking: Eliminates sampling errors during switching transitions}

 

^{3.Multiple Protection Mechanisms}

^{Thermal Shutdown Protection: Automatically halts operation when temperature exceeds threshold}

^{Current Limit Comparator: Monitors and limits peak current in real-time}

^{Feedback Detection Circuit: Enables precise voltage/current control through FB pin}

 

 

^{Operating Characteristics:}

^{Utilizes on/off control to achieve high efficiency at light loads}

^{Integrates a 700V-rated power MOSFET}

^{Supports cycle skipping for output voltage regulation}

 

 

 

^{Typical Advantages:
This integrated design significantly simplifies peripheral circuits while ensuring performance and providing comprehensive protection features, making it particularly suitable for compact and high-efficiency power supply solutions.}

 

^{IV. Schematic Diagram of General Test Circuit}

 

 

 

^{The universal test circuit for the LNK364PN adopts a typical flyback topology, suitable for validating the chip's fundamental performance and conducting design verification.}

 

^{Circuit Topology Structure:}

^{Input Stage: 85-265VAC wide-range AC input}

^{Rectification & Filtering: Bridge rectifier + electrolytic capacitor filtering}

^{Core Power Stage: Flyback converter topology}

^{Output Stage: Secondary rectification + LC filtering}

^{Feedback Network: Optocoupler isolated feedback}

 

^{Key Test Point Configuration:}

^{1.Input Characteristic Test Points}

^{TP1: AC input voltage monitoring point}

^{TP2: Rectified DC voltage test point}

 

 

^{2.Chip Operating Status Test Points}

^{TP3: BYPASS pin voltage (normal range: 5.8V ± 0.5V)}

^{TP4: FEEDBACK pin voltage (reflects output load status）}

 

^{3.Output Performance Test Points}

^{TP5: Output voltage accuracy test}

^{TP6: Output ripple and noise measurement}

 

^{Core Component Parameter Ranges:}

^{Input capacitor C1: 4.7-22 μF / 400 V}

^{Output capacitor C2: Selected based on output power requirements}

^{Feedback voltage divider resistors: Configured according to output voltage needs}

^{Transformer turns ratio: Calculated based on input and output voltage ranges}

 

 

V. Detailed Analysis of 2W Universal Input Constant Voltage (CV) Adapter Circuit

 

^{Overall Circuit Architecture. This design employs a non-isolated Buck topology, leveraging the high integration of the LNK364PN to create a compact and efficient 2W constant voltage adapter solution.}

 

 

^{Circuit Module Analysis}

 

^{1. Input Protection and Rectification Filtering Module}

^{RF1: Fusible resistor providing input overcurrent protection and inrush current limiting}

^{D1-D4: Form a bridge rectifier circuit converting AC input to DC}

^{C1, C2: Input filter capacitors smoothing the rectified DC voltage}

^{L2: Buck topology energy storage inductor, forming an LC filter network with subsequent circuits}

 

^{2. Buck Power Conversion Module}

^{Switching Control: The 700V MOSFET integrated in LNK364PN performs high-frequency switching}

^{Energy Transfer: Energy is stored and released through inductor L2}

^{Output Voltage: Determined by both the switching duty cycle and feedback signal}

 

^{3. Feedback and Voltage Regulation Module}

^{VR1: 5.1V precision Zener diode providing voltage reference
R1: Current-limiting resistor protecting the FB pin
FB Pin: Receives feedback signal to adjust switching duty cycle}

 

^{4. Performance Specifications Summary}

 

Parameter	Specification	Remarks
Input Voltage Range	85-265 VAC	Universal Input
Output Voltage	5.1 V ±2%	Adjustable
Output Power	2 W (max)	Continuous Output
No-load Power Consumption	<70 mW	@265 VAC Input
Efficiency	>70%	Full Range Average
Protection Features	Overcurrent/Overheat/Open Loop	Auto-recovery

 

 

 

 

 

^{Key Function Analysis}

^{Constant Voltage Control Mechanism}

^{When output voltage exceeds 5.1V, Zener diode VR1 conducts}

^{FB pin voltage rises, causing the chip to reduce switching duty cycle}

^{Output voltage returns to set value, achieving precise voltage regulation}

 

^{Protection Function Implementation}

^{Overcurrent Protection: Internal current limit comparator provides real-time monitoring}

^{Over-temperature Protection: Automatic shutdown when junction temperature exceeds threshold}

^{Input Undervoltage Protection: BP pin voltage monitoring ensures proper startup}

 

^{Efficiency Optimization Features}

^{On/Off Control: Skips switching cycles under light loads to reduce power consumption}

^{Frequency Jittering: Spreads EMI spectrum to simplify filter design}

^{Low Standby Power: <70mW no-load consumption at 265VAC input}

 

^{Performance Specifications}

^{Input Range: 85-265VAC (Universal)}

^{Output Voltage: 5.1V ±2%}

^{Output Power: 2W (Maximum Continuous)}

^{Efficiency: >70% (Full Voltage Range)}

^{Protection: Overcurrent, Overtemperature, Open Loop Protection}

 

^{Application Scenarios:}

^{Power supply for small household appliance control boards}

^{Power adapter for IoT devices}

^{Power supply for smart home sensors}

^{Low-cost charger solutions}

 

 

VI. Flyback Converter PCB Layout Guide

 

^{Top-Layer Layout Planning}

 

^{Safety Isolation Zoning Layout}

^{Primary-side Hazard Zone: High-voltage input area on the left side}

^{Input filter capacitors}

^{Transformer primary winding path}

 

^{Secondary-side Safety Zone: Low-voltage output area on the right side
Output rectification components
Output filter capacitors}
 

^{Isolation barrier: Central optocoupler isolation channel}

 

^{Key Component Layout Specifications}
 

^{1. Primary-side Power Path}

^{Minimize power loop area}

^{Source pin directly connected to thermal copper pad}

 

^{2. Secondary-side output path}

^{Keep output loops short and straight}

^{Place filter capacitors close to output terminals}

 

^{3. Feedback and Control Traces}

^{Place optocoupler close to transformer}

^{Route FB signal away from noise sources}

^{Mount BP bypass capacitor directly at chip pins}

 

 

 

^{Thermal Management Design}

 

^{Heat Dissipation Copper Optimization}

^{Large-area copper pour at source pin (shaded area in diagram)}

^{Recommended copper thickness: 2oz}

^{Add thermal vias when necessary}

 

^{Thermal Distribution Strategy}

^{Even distribution of power components}

^{Prevention of thermal concentration}

^{Reserved airflow space}

 

^{EMI Suppression Measures}

^{1. Noise Control}

^{Connect Y-capacitor at closest point}

^{Single-point connection between primary and secondary grounds}

^{Shielding protection for sensitive signals}

 

^{2. Layout Optimization}

^{Minimize high-frequency loop area}

^{Separate digital and analog grounds}

^{Route clock signals away from analog sections}

 

^{3.Safety Spacing Requirements}

^{Primary-to-secondary clearance: ≥6.4mm}

^{High-voltage spacing: ≥3.2mm}

^{Creepage distance compliant with IEC 60950}

 

^{4.Design for Manufacturing}

^{Component spacing compliant with automated production requirements}

^{Test points accessible for in-circuit testing}

^{Avoid solder mask application over heat dissipation areas}

 

^{5.Electrical Performance Verification}

^{Power loop impedance}

^{Signal integrity}

^{Power integrity}

 

^{This layout solution ensures optimal performance of the LNK364PN in flyback converters through optimized component placement, thermal management, and EMI design, while meeting safety regulations and manufacturability requirements.}

 

 

^{VII. Output Enable Timing Analysis}

 

 

 

^{Key Signal Analysis in Timing Diagram:}

^{1. Feedback (FB) Voltage Timing}

^{Enable Threshold: Output enable activates when FB voltage drops to 1.3V}

^{Disable Threshold: Output enable deactivates when FB voltage rises to 1.5V}

^{Hysteresis Window: 200mV hysteresis prevents switching chatter}

 

^{2. Internal DCMAX Signal}

^{Maximum Duty Cycle Control: DCMAX limits the maximum on-time}

^{Safety Protection: Prevents transformer saturation and component overstress}

^{Dynamic Adjustment: Automatically optimizes based on input voltage}

 

^{3. Drain Voltage (VDRAIN) Waveform}

^{Switching Start: Commences switching operation after FB enable}

^{Switching Termination: Immediately stops switching after FB disable}

^{Waveform Characteristics: Typical flyback switching waveform}

 

 

^{Control Mechanism Details:}

^{Enable Process:}

^{FB voltage drops to the 1.3V threshold due to output demand}

^{Chip immediately initiates switching operation}

^{PWM waveform appears at VDRAIN}

^{Output voltage starts to build up}

 

^{Disable Process:}

^{Output voltage reaches set value, FB voltage rises to 1.5V}

^{Chip immediately stops switching operation}

^{VDRAIN maintains high-impedance state}

^{System enters low-power standby mode}

 

^{Design Essentials:}

^{Feedback Network Optimization}

^{Ensure FB response speed meets dynamic load requirements}

^{Set voltage divider resistors appropriately to avoid false triggering}

^{Add proper filtering to enhance noise immunity}

 

^{Protection Function Integration}

^{Overload protection takes priority over enable control}

^{Thermal protection immediately disables output}

^{Auto-restart cycle coordinates with enable timing}

 

^{Performance Impact Factors}

^{FB signal slope affects response speed}

^{Load transient characteristics determine enable frequency}

^{Input voltage variations influence maximum duty cycle}

 

^{This timing mechanism ensures the LNK364PN can rapidly respond to load variations while maintaining high efficiency and stability, delivering precise power control for the system.}

 

 

 

VIII. Pin Configuration and Functional Analysis

 

1. Universal Pin Functions (Common Across All Packages)
The core functional pins of the LinkSwitch-XT series maintain consistent functionality across all package types, with variations only in physical layout. Key pins and their functions include:

 

^{S (Source):
The source terminal of the power switch, typically connected to ground, serves as the reference ground for the power loop and the common ground for the internal circuitry. The multiple "S" pins shown in the diagram represent parallel-connected source pins, which reduce on-state resistance and enhance current-carrying capacity.}

^{BP (Bypass):
This pin connects to an external bypass capacitor (typically 0.1μF) to provide a stable bias voltage for the internal circuitry of the chip. It also filters high-frequency noise, ensuring reliable operation of internal components (e.g., oscillators and comparators).}

^{FB (Feedback):
This pin receives the output voltage feedback signal. By monitoring changes in the output voltage, the chip dynamically adjusts the switching frequency/duty cycle to achieve voltage regulation (serving as the core input for closed-loop voltage control).}

^{D (Drain):
The drain terminal of the power switch, connected to the primary winding of the transformer or the high-voltage input end. It serves as the core node of the high-voltage power loop, controlling the transfer of energy from input to output.}

 

^{2. Package Variation Description
P Package (DIP-8B):
Dual in-line package (DIP) suitable for traditional through-hole soldering processes. Pins extend from both sides of the chip, with "3a" in the diagram illustrating its pin layout, facilitating manual soldering and debugging.}

 

^{G Package (SMD-8B):
Surface-mount device (SMD) package with gull-wing leads, suitable for automated SMT production lines. Offers more compact dimensions. While not explicitly shown in the diagram, its functionality is identical to the P package.}

 

^{D Package (SO-8C):
Small Outline package (SOIC). The diagram label "3b" indicates its pin layout. As a more compact surface-mount package, it is widely used in consumer electronics and space-constrained power supplies.}

 

^{Significance for LNK364PN}

^{The LNK364PN adopts the P package (DIP-8B), which means:}

^{The pin layout labeled "3a" in the diagram (positions of S, BP, FB, D) directly corresponds to the physical pins of the LNK364PN.}

^{Engineers can use this diagram to quickly identify "which pin connects to feedback" and "which pin connects to high-voltage input" during circuit design and chip soldering, preventing functional misassignment of pins.}

 

^{Design Guidance Value}
 

^{This pin configuration diagram serves as a "hardware design dictionary":}

^{During schematic design, this diagram determines the connection relationships between chip pins and peripheral components (such as feedback resistors, bypass capacitors, and transformers).}

 

^{During PCB layout, the pin sequence in this diagram must be matched to ensure proper chip functionality after soldering.}

 

^{During debugging, if power output is abnormal, this diagram enables quick identification of issues such as "poor solder contact at the feedback pin" or "incorrect drain pin connection".}

 

^{Typical Application Connections}

^{High-voltage DC input → Transformer → D pin (power input) Output voltage sampling → Optocoupler → FB pin (feedback control) BP pin → 100nF capacitor → S pin (internal power supply) S pin → Large-area copper pour → Power ground (thermal path)}

 

^{This pin configuration ensures the LNK364PN delivers efficient power conversion while providing comprehensive protection features and flexible design options, making it an ideal choice for compact switching power supply designs.}

 

^{Technical Differentiation Advantages}

 

^{The LNK364PN demonstrates three core technical advantages over comparable products:}

^{1.Revolutionary Clamp-less Design
Utilizing an innovative 700V integrated MOSFET with intelligent drain sensing technology, it completely eliminates the traditional RCD snubber network required in flyback circuits. While ensuring system reliability, it significantly reduces BOM costs and PCB area.}

 

^{2.Intelligent Feedback Control Architecture}

^{Implements an innovative control strategy combining on/off control with frequency jitter}

^{Achieves <70mW no-load power consumption while maintaining excellent load response characteristics}

^{Unique optocoupler-free feedback mechanism significantly simplifies circuit structure without compromising performance}

 

^{3.Fully Integrated Protection Ecosystem}

^{Integrates over-temperature, over-current, open-loop protection, and auto-restart functions in a single chip}

^{Features forward-looking design with output over-voltage protection capability}

^{All protection parameters are factory-calibrated to ensure system consistency}

 

^{These differentiated technologies establish the LNK364PN as a new technical benchmark in sub-2W power supply applications, delivering industry-leading power density and reliability balance for cost-sensitive applications.}