NS公司的LM3421/LM3423是多用途高壓LED驅動,可以配置成降壓,升壓,降壓-升壓(反激)或SEPIC拓撲,輸入電壓從4.5V到高達75V,可調開關頻率高達2MHz,具有快速(50kHz) PWM調光,關斷電流小于1uA,可用在LED驅動器和多種恒流模式穩壓器以及熱電冷卻驅動器.本文介紹了LM3421/LM3423的住要特性,方框圖以及多種應用電路圖,升壓評估板主要特性和電路圖和材料清單(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.

LM3421-3主要特性:
■VIN range from 4.5V to 75V
■2% Internal reference voltage (1.235V)
■Current 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)

LM3421-3應用:
■LED Drivers
■Constant-Current Buck-Boost Regulator
■Constant-Current Boost Regulator
■Constant-Current Flyback Regulator
■Constant-Current SEPIC Regulator
■Thermo-Electric Cooler (Peltier) Driver
可參考附件中的拓撲圖

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