原标题：NS LM5118宽电压升/降压电源方案

　　NS公司的LM5118是宽电压升压/降压开关电源控制器,它集成了实现高性能高性价比的降压/升压稳压器所需的所有功能,从而是外接元件数最少. LM5118的工作电压从3.5V到75V,可编程开关频率可高达到500kHz,具有可编程软起动时间,超低的关断电流和热保护等功能,具有广泛的用途.本文介绍了LM5118的主要特性,方框图以及典型的应用电路图和LM5118评估板的主要性能和详细的电路图以及所用材料清单(BOM).

　　The LM5118 wide voltage range Buck-Boost switching regulator controller features all of the functions necessary to implement a high performance, cost efficient Buck-Boost regulator using a minimum of external components. The Buck-Boost topology maintains output voltage regulation when the input voltage is either less than or greater than the output voltage making it especially suitable for automotive applications. The LM5118 operates as a buck regulator while the input voltage is sufficiently greater than the regulated output voltage and gradually transitions to the buck-boost mode as the input voltage approaches the output. This dual mode approach maintains regulation over a wide range of input voltages with optimal conversion efficiency in the buck mode and a glitch-free output during mode transitions. This easy to use controller includes drivers for the high side buck MOSFET and the low side boost MOSFET. The regulator’s control method is based upon current mode control utilizing an emulated current ramp. Emulated current mode control reduces noise sensitivity of the pulse-width modulation circuit, allowing reliable control of the very small duty cycles necessary in high input voltage applications. Additional protection features include current limit, thermal shutdown and an enable input. The device is available in a power enhanced TSSOP-20 package featuring an exposed die attach pad to aid thermal dissipation.

　　LM5118主要特性:

　　■ Ultra-wide input voltage range from 3V to 75V

　　■ Emulated peak current mode control

　　■ Smooth transition between step-down and step- up modes

　　■ Switching frequency programmable to 500KHz

　　■ Oscillator synchronization capability

　　■ Internal high voltage bias regulator

　　■ Integrated high and low-side gate drivers

　　■ Programmable soft-start time

　　■ Ultra low shutdown current

　　■ Enable input wide bandwidth error amplifier

　　■ 1.5% feedback reference accuracy

　　■ Thermal shutdown

图1.LM5118方框图和典型应用电路图

图2.12V/3A典型应用电路图

　　LM5118数据表请见:

　　>http://cache.national.com/ds/LM/LM5118.pdf

　　LM5118评估板

　　The LM5118 evaluation board is designed to provide the design engineer with a fully functional, Emulated Current Mode Control, buck-boost power converter to evaluate the LM5118 controller IC. The evaluation board provides a 12V output with 3A of output current capability. The evaluation board’s wide input voltage range is from 75V to 5V, with operation down to 3V with some component changes. The evaluation board operates at 300 kHz, a good compromise between conversion efficiency, tradeoffs between buck and buck-boost mode requirements, and converter size. The printed circuit board consists of 4 layers with 2 ounce copper top and bottom, and 1 ounce copper on internal layers. The board is constructed with FR4 material. This application note contains the evaluation

　　board schematic, Bill -of-Materials (BOM) and a quick setup procedure. Refer to the LM5118 data sheet and quick start for more complete circuit and design information.

　　LM5118 IC特性:

　　Integrated high and low side driver

　　Internal high voltage bias regulator

　　Ultra-wide input voltage range: 5V to 75V

　　Emulated current mode control

　　Single inductor architecture

　　VOUT operation below and above VIN

　　Single resistor sets oscillator frequency

　　Oscillator synchronization capability

　　Programmable soft-start

　　Ultra low (<10 μA) shutdown current

　　Enable input

　　Wide bandwidth error amplifier

　　Adjustable output voltage 1.23V-75V

　　1.5% feedback reference accuracy

　　Thermal Shutdown

　　No VIN to VOUT connection during fault protection

图3. LM5118应用框图

图4. LM5118评估板电路图

　　下表为LM5118评估板材料清单(BOM)