原标题：Maxim MAX17498A峰值电流模式电源转换方案

　　Maxim 公司的MAX17498A/B/C是用于反激/升压电源的峰值电流模式AC/DC和DC/DC电源转换器，包括了设计宽输入电压隔离和非隔离电源的所有控制电路，MAX17498A/MAX17498C反激转换器的工作频率250kHz，MAX17498B反激/升压转换器的工作频率500kHz，具有极好的瞬态响应特性，主要用在工业应用的前端AC/DC电源，通信电源等。本文介绍了MAX17498A/MAX17498B/MAX17498C主要特性和优势，方框图和多种起动电路，以及智能电表和PLC电源的应用案例。

　　The MAX17498A/MAX17498B/MAX17498C devices are current-mode fixed-frequency flyback/boost converters with a minimum number of external components. They contain all the control circuitry required to design wide-input-voltage isolated and nonisolated power supplies. The MAX17498A has its rising/falling undervoltage lock­out (UVLO) thresholds optimized for universal offline (85V AC to 265V AC) applications, while the MAX17498B/ MAX17498C support UVLO thresholds suitable to low-voltage DC-DC applications.

　　The switching frequency of the MAX17498A/MAX17498C flyback converters is 250kHz, while that of the MAX17498B flyback/boost converter is 500kHz. These frequencies allow the use of tiny magnetic and filter components, resulting in compact, cost-effective power supplies. An EN/UVLO input allows the user to start the power supply precisely at the desired input voltage, while also function­ing as an on/off pin. The OVI pin enables implementation of an input overvoltage-protection scheme that ensures that the converter shuts down when the DC input voltage exceeds the desired maximum value.

　　The devices incorporate a flexible error amplifier and an accurate reference voltage (REF) to enable the end user to regulate both positive and negative outputs. Programmable current limit allows proper sizing and protection of the primary switching FET. The MAX17498B supports a maxi­mum duty cycle of 92% and provides programmable slope compensation to allow optimization of control-loop performance. The MAX17498A/MAX17498C support a maximum duty cycle of 49%, and have fixed internal slope compensation for optimum control-loop performance. The devices provide an open-drain PGOOD pin that serves as a power-good indicator and enters the high-impedance state to indicate that the flyback/boost converter is in regula­tion. An SS pin allows programmable soft-start time for the flyback/boost converter. Hiccup-mode overcurrent pro­tection and thermal shutdown are provided to minimize dissipation under overcurrent and overtemperature fault conditions. The devices are available in a space-saving, 16-pin (3mm x 3mm) TQFN package with 0.5mm lead spacing.

　　MAX17498A/MAX17498B/MAX17498C主要特性和优势：

　　Peak Current-Mode Flyback/Boost Converter

　　Current-Mode Control Provides Excellent Transient Response

　　Fixed Switching Frequency

　　250kHz (MAX17498A/MAX17498C)

　　500kHz (MAX17498B)

　　Flexible Error Amplifier to Regulate Both Positive and Negative Outputs

　　Programmable Soft-Start to Reduce Input Inrush Current

　　Programmable Voltage or Current Soft-Start

　　Power-Good Signal (PGOOD)

　　Reduced Power Dissipation Under Fault

　　Hiccup-Mode Overcurrent Protection

　　Thermal Shutdown with Hysteresis

　　Robust Protection Features

　　Flyback/Boost Programmable Current Limit

　　Input Overvoltage Protection

　　Optimized Loop Performance

　　Programmable Slope Compensation for Flyback /Boost Maximizes Obtainable Phase Margin

　　High Efficiency

　　175mI, 65V Rated n-Channel MOSFET Offers Typical Efficiency Greater Than 80%

　　No Current-Sense Resistor

　　Optional Spread Spectrum

　　Space-Saving, 16-Pin (3mm x 3mm) TQFN

　　Package

　　MAX17498A/MAX17498B/MAX17498C应用：

　　Front-End AC-DC Power Supplies for Industrial Applications (Isolated and Nonisolated)

　　Telecom Power Supplies

　　Wide-Range DC Input Flyback/Boost Industrial Power Supplies

　　图1。MAX17498A/MAX17498B/MAX17498C方框图

　　图2。MAX17498A 基于RC的起动电路

　　图3。MAX17498A 基于电流源的起动电路

　　图4。MAX17498B/C采用偏压绕组关断Q1和降功耗的起动电路

　　图5。MAX17498B/C采用输入IN直接连接带DC输入的起动电路

　　图6。MAX17498A典型应用电路(智能电表电源)

　　图7。MAX17498B典型应用电路(PLC电源)

　　图8。MAX17498C典型应用电路