原标题：Linear LTC3614 4A 4MHz同步降压电源解决方案

　　LTC3614是Linear公司的4A 4MHz同步降压DC/DC转换器,采用电流模式和固定频率架构.无负载睡眠模式的电流为75uA,输入电压从2.25V到5.5V,100%占空比,工作频率可编程到4MHz,允许使用小型SMT电感器.输出电压精度±1%,电压可低至0.6V,效率高达95%,主要用在POL电源,分布电源,手提计算机电源,DDR存储器电源和手持设备.本文介绍了LTC3614主要特性,方框图以及多种应用电路.

　　4A, 4MHz Monolithic Synchronous Step-Down DC/DC Converter

　　The LTC3614 is a low quiescent current monolithic synchronous buck regulator using a current mode, constant frequency architecture. The no-load DC supply current in sleep mode is only 75μA while maintaining the output voltage (Burst Mode operation) at no load, dropping to zero current in shutdown. The 2.25V to 5.5V input supply voltage range makes the LTC3614 ideally suited for single Li-Ion as well as fixed low voltage input applications. 100% duty cycle capability provides low dropout operation, extending the operating time in battery-powered systems.

　　The operating frequency is externally programmable up to 4MHz, allowing the use of small surface mount inductors. For switching-noise-sensitive applications, the LTC3614 can be synchronized to an external clock at up to 4MHz.

　　Forced continuous mode operation in the LTC3614 reduces noise and RF interference. Adjustable compensation allows the transient response to be optimized over a wide range of loads and output capacitors.

　　The internal synchronous switch increases efficiency and eliminates the need for an external catch diode, saving external components and board space. The LTC3614 is offered in a leadless 24-pin 3mm x 5mm thermally enhanced QFN package.

　　LTC3614主要特性:

　　4A Output Current

　　2.25V to 5.5V Input Voltage Range

　　Low Output Ripple Burst Mode Operation: IQ = 75μA

　　±1% Output Voltage Accuracy

　　Output Voltage Down to 0.6V

　　High Efficiency: Up to 95%

　　Low Dropout Operation: 100% Duty Cycle

　　Programmable Slew Rate on SW Node Reduces Noise and EMI

　　Adjustable Switching Frequency: Up to 4MHz

　　Optional Active Voltage Positioning (AVP) with Internal Compensation

　　Selectable Pulse-Skipping/Forced Continuous/Burst Mode Operation with Adjustable Burst Clamp

　　Programmable Soft-Start

　　Inputs for Start-Up Tracking or External Reference

　　DDR Memory Mode, IOUT = ±3A

　　Available in a 24-Pin 3mmx 5mm QFN Thermally Enhanced Package

　　LTC3614应用:

　　Point-of-Load Supplies

　　Distributed Power Supplies

　　Portable Computer Systems

　　DDR Memory Termination

　　Handheld Devices

　　图1.LTC3614方框图

　　图2.LTC3614 1.8V/4A降压稳压器电路图

　　图3.快速补偿和改进瞬变响应2.25MHz通用降压稳压器电路图

　　图4.采用1MHz外接时钟的主从跟踪输出电路图