原标题：NS LM3429 RD-173 LED驱动方案

　　NS公司的RD-173 - MR16 和PAR38 LED灯参考设计采用LM3429多功能高压LED控制器和LM2841/42 PWM DC/DC 降压稳压器. LM3429的输入电压可从4.5V到75V,具有快速(50kHz) PWM 调光特性;而LM2841/42的输入电压从表面上看4.5V到42V,输出电流300mA或600mA可选择.RD-173 - MR16 和PAR38 LED灯参考设计输入电压为9V到36V,这样可采用12V和24V电源,以适应各种应用,可驱动1-12个串联连接的LED,驱动电流高达1A.本文介绍了LM3429和LM2841/42的主要特性以及典型应用电路.此外还未集中介绍了RD-173 - MR16 和PAR38 LED灯参考设计的主要特性, 外形图,详细电路图和所用元件清单和PCB布局图.

　　LM3429: N-Channel Controller for Constant Current LED Drivers

　　The LM3429 is a versatile high voltage LED driver controller. With the capability to be configured in a Buck, Boost, Buck- Boost (Flyback), or SEPIC topology, and an input and output operating voltage rating of 75V, the LM3429 is ideal for illuminating LEDs in a very diverse, large family of applications.

　　Adjustable high-side current sense with a typical sense voltage of 100 mV allows for tight regulation of the LED current with the highest efficiency possible. Output LED current regulation is based on peak current-mode control with predictive Off-Time Control. This method of control eases the design of loop compensation while providing inherent input voltage feed-forward compensation.

　　The LM3429 includes a high-voltage startup regulator that operates over a wide input range of 4.5V to 75V. The internal PWM controller is designed for adjustable switching frequencies of up to 2.0MHz, thus enabling compact solutions. Additional features include: precision reference, logic compatible DIM input suitable for fast PWM dimming, cycle-by-cycle current limit, and thermal shutdown.

　　The LM3429 comes in a low profile, thermally efficient TSSOP EP 14-lead package.

　　LM3429主要特性:

　　■ VIN range from 4.5V to 75V

　　■ 2% Internal reference voltage (1.235V)

　　■ Current sense voltage adjustable from 20 mV

　　■ High-side current sensing

　　■ 2Ω MOSFET gate driver

　　■ Dimming MOSFET gate driver

　　■ Input under-voltage protection

　　■ Over-voltage protection

　　■ Low shutdown current, IQ < 1μA

　　■ Fast (50kHz) PWM dimming

　　■ Cycle-by-cycle current limit

　　■ Programmable switching frequency

　　■ TSSOP EP 14-lead package

　　LM3429应用:

　　■ LED Drivers

　　■ Constant-Current Buck-Boost Regulator

　　■ Constant-Current Boost Regulator

　　■ Constant-Current Flyback Regulator

　　■ Constant-Current SEPIC Regulator

　　■ Thermo-Electric Cooler (Peltier) Driver

图1. LM3429典型应用电路

　　The LM2841 and LM2842 are PWM DC/DC buck (step-down) regulators. With a wide input range from 4.5V-42V, they are suitable for a wide range of applications such as power conditioning from unregulated sources. They feature a low RDSON (0.9Ω typical) internal switch for maximum efficiency (85% typical). Operating frequency is fixed at 550 kHz (X version) and 1.25 MHz (Y version) allowing the use of small external components while still being able to have low output voltage ripple. Soft-start can be implemented using the shutdown pin with an external RC circuit allowing the user to tailor the soft-start time to a specific application.

　　The LM2842 is optimized for up to 600 mA load currents while the LM2841 is optimized for up to 300 mA load current. Both have a 0.765V nominal feedback voltage.

　　Additional features include: thermal shutdown, VIN under-voltage lockout, and gate drive under-voltage lockout. The LM2841 and LM2842 are available in a low profile TSOT-6L package.

　　LM2841和LM2842主要特性:

　　■ Input voltage range of 4.5V to 42V

　　■ Output current options of 300 mA and 600 mA

　　■ Feedback pin voltage of 0.765V

　　■ 550 kHz (X) or 1.25 Mhz (Y) switching frequency

　　■ Low shutdown IQ, 16 μA typical

　　■ Short circuit protected

　　■ Internally compensated

　　■ Soft-start circuitry

　　■ Small overall solution size (TSOT-6L package)

　　LM2841和LM2842应用:

　　■ Battery powered equipment

　　■ Industrial distributed power applications

　　■ Portable media players

　　■ Portable hand held instruments

图2. LM2841和LM2842方框图

图3.LM2841/42应用电路, 5V 输出

　　RD-173 - MR16 和PAR38 LED灯参考设计

　　RD-173 - MR16 and PAR38 LED Bulb Reference Design Using National`s LM3429 LED Driver and the Nuventix SynJet Coolers

　　The demonstration board includes a LM3429 device that converts 9VDC to 36VDC input to a 700mA constant current output designed to operate a load of three to four series LEDs.

　　This reference design is ideal for any LED application that runs off of a 12V or 24V rail. This is a 4-layer board having input voltage and ground as the two internal planes. The design has been made assuming there are analog dimming requirements.

　　This design works with the Nuventix SynJet module which serves as the cooling element for an LED luminaire or bulb replacement for the standard MR16, PAR20, PAR25, PAR30 or PAR38 form factors

　　RD-173 - MR16 和PAR38 LED灯参考设计主要特性:

　　■ The LM3429 buck-boost LED driver:

　　— Allows input voltage capability of 9V-36V to accommodate 12V and 24V voltage rails for a variety of applications

　　— Drives 1-12 series connected LEDs up to 1A

　　— Enables analog dimming capability of 0 mA to 1A with a potentiometer or 1V to 10V dimming

　　■ The LM2842 voltage regulator provides a regulated 5V power supply to the SynJet actuator

　　图4. RD-173 - MR16 和PAR38 LED灯参考设计外形图

　　Nuventix 参考设计材料清单(BOM):