高效率同步整流电源管理IC——AX3502(0.6A)/AX3503(1A)/AX3504(2A)
AX3502/3503/3504系列为电流模式(current mode)构造，脉波宽度调变输出的同步直流转换器，内部切换频率高达1.5MHz，不但可以省略一颗外部二极管元件，还可以大幅缩小外部元件，缩小电路板空间及节省元件成本。输入电压范围可由最低2.5伏特到最高5.5伏特，输出电压可以依需要调整最低可以至0.6伏特，而待机电流最大不会超过1毫安，非常适合于手持式产品， PDA，MP3 Player，数码相机，智能型手机...等装置的电压转换。
AX3502/3503/3504应用上可提供高转换效能及稳定的工作电压，工作效率可高达96%， 其内部具有完整的系统保护功能包括短路保护(SCP) 、过温度保护(OTP)及过电流保护(OCP)功能。。
 
AX3502采用标准的SOT23-5L无铅封装与AX3503 采用标准的SOT23-5L 和SOT89-5L无铅封装，AX3504采用标准的SOP-8L与3×3mm DFN-10L无铅封装体积小而且极少的外部元件可大幅缩小印刷电路板的面积，而且具有高效率， 可大幅减小IC元件表面温度以符合客户需求。

AX3503-1.5MHz,1A Synchronous Step-Down ConverterDataSheet

GENERAL DESCRIPTION
    AX3503 is a high efficiency monolithic synchronous buck regulator using a constant frequency, current mode architecture. The device is available in an adjustable version. Supply current with no load is 350uA and drops to <1uA in shutdown. The 2.5V to 6V input voltage range makes AX3503 ideally suited for single Li-Ion, two to four AA battery-powered applications. 100% duty cycle provides low dropout operation, extending battery life in portable systems. PWM pulse skipping mode operation provides very low output ripple voltage for noise sensitive applications. Switching frequency is internally set at 1.5MHz, allowing the use of small surface mount inductors and capacitors. The internal synchronous
switch increases efficiency and decreases need of an external Schottky diode. Low output voltages are easily supported with the 0.6V feedback reference voltage. AX3503 is available in small SOT23-5L, TSOT23-5L and TDFN-8L (3*3) packages.

FEATURES
- 2.5V to 6V Input Voltage Range
- High Efficiency: Up to 96%
- 1.5MHz Constant Frequency Operation
- 1A Output Current at VIN=3.6V and VOUT=1.8V
- Quiescent Current: 350uA (input < 4.2V)
- No Schottky Diode Required
- 100% Duty Cycle in Dropout
- 0.6V Reference Allows Low Output Voltages
- Current Mode Operation for Excellent Line and Load Transient Response
- Current limit, Enable function
- Short Circuit Protect (SCP)
- ≤ 1μA Shutdown Current
- SOT23-5L, TSOT23-5L and TDFN-8L (3*3) Pb-Free packages