NS的LM3421/LM3423是恒流LED驱动器的N沟控制器,可配置成降压,升压,降-升压(反激)或SEPIC,输入电压可高达75V,非常适合各种情况下的LED照明应用. 采用LM3423的环境光自适应LED驱动器采用4.5V-12V的电池输入,在15-20V时LED保持100mA的恒流,效率高达85%,PWM标LED调光高达25kHz,可使LED的亮度正比与环境光,从而延长了电池使用寿命.本文介绍了LM3421/LM3423的主要特性,方框图以及相应的应用电路.同时还介绍了采用LM3423的环境光自适应LED驱动器的主要特性,详细的电路图和材料清单(BOM).

　　LM3421, LM3423: N-ChannEL Controllers for Constant Current LED Drivers

　　The LM3421/LM3423 devices are versatile high voltage LED driver controllers. With the capability to be configured in a Buck, Boost, Buck-Boost (Flyback), or SEPIC topology, and an input operating voltage rating of 75V, these controllers are ideal for illuminating LEDs in a very diverse, large family of applications.

　　Adjustable high-side current sense with a typical sense voltage of 100mV 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 LM3421/LM3423 include 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: zero current shutdown, precision reference, logic compatible DIM input suitable for fast PWM dimming, cycle-by-cycle current limit, and thermal

　　shutdown.

　　The LM3423 also includes an LED output status flag, a fault flag, a programmable fault timer, and a logic input to select the polarity of the dimming output driver.

　　LM3421/LM3423主要特性:

　　■VIN range from 4.5V to 75V

　　■2% Internal reference voltage (1.235V)

　　■urrent sense voltage adjustable from 20mV

　　■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

　　■LED output status flag (LM3423 only)

　　■Fault timer pin (LM3423 only)

　　■TSSOP EP 16-lead package (LM3421)

　　■TSSOP EP 20-lead package (LM3423)

　　LM3421/LM3423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