OnSemiNPC1562100W，48V，DC/DC轉換器參考設計方案

OnSemi公司的NCP1562是一款高效、外圍器件少的DC/DC電壓模式轉換控制器芯片。控制器包含兩同相輸出，通過一個重疊延遲來保護同時導通，有力于軟開關。主輸出主要驅動初級前向轉換MOSFET。次輸出主要驅動有源鉗位電路MOSFET，次級主要由一個同步整流器或由一個半橋電路組成。NCP1562與眾不同的特性是軟停止和時間閥值內(nèi)循環(huán)跳躍電流限制。軟停止控制方式是在檢測到有嚴重的故障時，軟停止電路系統(tǒng)停止對轉換器供電。循環(huán)跳躍電流限制方式是在連續(xù)出現(xiàn)過流故障時，循環(huán)跳躍檢測器使能連續(xù)軟停止。本文主要介紹了該芯片的主要特性及功能強大的保護特性，并給出芯片內(nèi)部框圖、方案介紹、方案原理圖、方案PCB圖及元器件列表。

The NCP1562x is a family of voltage mode controllers designed for dc--dc converters requiring high--efficiency and low parts count. These controllers incorporate two in phase outputs with an overlap delay to prevent simultaneous conduction and facilitates soft switching. The main output is designed for driving a forward converter primary MOSFET. The secondary output is designed for driving an active clamp circuit MOSFET, a synchronous rectifier on the secondary side, or an asymmetric half bridge circuit.

The NCP1562 family reduces component count and system size by incorporating high accuracy on critical specifications such as maximum duty cycle limit, undervoltage detector and overcurrent threshold. Two distinctive features of the NCP1562 are soft--stop and a cycle skip current limit with a time threshold. Soft--stop circuitry powers down the converter in a controlled manner if a severe fault is detected. The cycle skip detector enables a soft--stop sequence if a continuous overcurrent condition is present.

Additional features found in the NCP1562 include line feed--forward, frequency synchronization up to 1.0 MHz, cycle--by—cycle current limit with leading edge blanking (LEB), independent under and overvoltage detectors, adjustable output overlap delay, programmable maximum duty cycle, internal startup circuit and soft--start.

NCP1562主要特性：

· Dual Control Outputs with Adjustable Overlap Delay
· >2.0 A Output Drive Capability
· Soft--Stop Powers Down Converter in a Controlled Manner
· Cycle--by--Cycle Current Limit
· Cycle Skip Initiated if Continuous Current Limit Condition Exists
· Voltage Mode Operation with Input Voltage Feedforward
· Fixed Frequency Operation up to 1.0MHz
· Bidirectional Frequency Synchronization
· Independent Line Undervoltage and Overvoltage Detectors
· Accurate Programmable Maximum Duty Cycle Limit
· Programmable Maximum Volt--Second Product
· Programmable Soft--Start
· Internal 100 V Startup Circuit
· Precision 5.0 V Reference
· These are Pb--Free Devices

NCP1562應用：

· Telecommunications Power Converters
· Low Output Voltage Converters using Control Driven Synchronous Rectifier
· Industrial Power Converters
· 42 V Automotive System
· ATX Power Supplies


圖1. NCP1562內(nèi)部方框圖

NCP1562-100WGEVB方案介紹：

The NCP1562 PWM controller contains all the features and flexibility needed to implement an active clamp forward dc?dc converter. This IC operates from an input supply up to 150 V, thus covering the input voltages usually found in telecom, datacom and 42 V automotive systems. One can also note that the NCP1562 can be used in mains related applications (e.g. desktop, server, flat TVs) as it can be supplied by an auxiliary power supply.

The NCP1562 is the ideal choice for new generation isolated fixed switching frequency dc?dc converters using the active clamp topology with synchronous rectification to achieve extremely high conversion efficiency. This controller will help designers cope with their daily challenge, “small form factor highly protected module” through the following features:

· Dual Outputs with Adjustable Overlap Delay:
provide design flexibility. Output 1 (OUT1) drives the main switch in a forward or flyback converter topology.Output 2 (OUT2) can be used to drive an active clamp/reset switch, a synchronous rectifier switch, or both. OUT2 has an adjustable overlap delay to prevent simultaneous conduction of the switching elements.

· Soft?Stop:
discharges the active clamp capacitor prior to turn off to eliminate unwanted oscillations.

· An Internal Startup Regulator:
provides power to the NCP1562 during startup. Once the system powers up, the regulator is disabled, thus reducing power consumption. The regulator can be powered directly from the input line.

· Soft?Start:
allows the system to turn on in a controlled manner and reduce stress on system components.

· Adjustable Maximum Duty Ratio:
allows the design to be optimized without a penalty on drain voltage. Duty ratio is controlled within ±5%.

· Adjustable Volt-second Limit:
prevents transformer saturation and improve transient response.

· Line Feedforward:
adjusts the duty ratio inversely proportional to line voltage, allowing the controller to respond in the same cycle to line voltage changes. It provides the controller some advantages of current-mode control, while eliminating noise susceptibility, low power jitter and the need for ramp compensation.

· Dual Mode Overcurrent Protection Circuit:
handles momentary and continuous overcurrent conditions differently to provide the best tradeoff in system performance and safety.

· Line Under/Overvoltage Detector:
circuits enable the device when the line voltage is within the pre-selected voltage range. A resistor divider from the input line biases the under and overvoltage detectors. The accurate UV limit allows the converter to operate at high duty ratio without creating additional component stresses.

NCP1562-100WGEVB方案原理圖：

圖2. NCP1562-100WGEVB方案原理圖

NCP1562-100WGEVB方案材料清單：




PCB元件布局圖：