NS 公司的LM3433是帶高頻調光的HBLED驅動器,為大功率LED提供了恒流照明.工作輸入電壓為-9V到-14V,輸出電流大于6A,PWM頻率大于30kHz,適用于共陽極LED,不需要輸出電容,開關頻率高達1MHz,靜態電流典型值為1mA,具有軟起動特性,可用于LCD背景光,投映系統,固態照明和汽車照明.本文介紹了LM3433主要特性,方框圖, 典型應用電路以及輸出電流2A – 6A 和2A - 14A應用電路和評估板電路圖與材料清單.

LM3433: Common Anode Capable High Brightness LED Driver with High Frequency Dimming
The LM3433 is an adaptive constant on-time DC/DC buck (step-down) constant current controller (a true current source). The LM3433 provides a constant current for illuminating
high power LEDs. The output configuration allows the anodes of multiple LEDs to be tied directly to the ground referenced chassis for maximum heat sink efficacy. The high
frequency capable architecture allows the use of small external passive components and no output capacitor while maintaining low LED ripple current. Two control inputs are used to modulate LED brightness. An analog current control input is provided so the LM3433 can be adjusted to compensate for LED manufacturing variations and/or color temperature correction.
The other input is a logic level PWM control of LED current. The PWM functions by shorting out the LED with a parallel switch allowing high PWM dimming frequencies. High
frequency PWM dimming allows digital color temperature control, interference blanking, field sequential illumination, and brightness control. Additional features include thermal
shutdown, VCC under-voltage lockout, and logic level shutdown mode. The LM3433 is available in a low profile LLP-24 package.

LM3433主要特性:
■ Operating input voltage range of -9V to -14V w.r.t. LED anode
■ Control inputs are referenced to the LED anode
■ Output current greater than 6A
■ Greater than 30kHz PWM frequency capable
■ Negative output voltage capability allows LED anode to be tied directly to chassis for maximum heat sink efficacy
■ No output capacitor required
■ Up to 1MHz switching frequency
■ Low IQ, 1mA typical
■ Soft start
■ Adaptive programmable ON time allows for constant ripple current
■ LLP-24 package

LM3433應用:
■ LCD backlighting
■ Projection systems
■ Solid state lighting
■ Automotive lighting

                          圖1.LM3433方框圖



圖2.LM3433典型應用電路




圖3.2A – 6A 輸出應用電路




圖4.2A - 14A 輸出應用電路

LM3433 4-20A LED驅動評估板

LM3433 4A to 20A LED Driver Evaluation Board
The evaluation board is designed to provide a constant current in the range of 4A to 20A. The LM3433 requires two input voltages for operation. A positive voltage with respect to GND is required for the bias and control circuitry and a negative voltage with respect to GND is required for the main power input. This allows for the capability of using common anode LEDs so that the anodes can be tied to the ground referenced chassis. The evaluation board only requires one input voltage of -12V with respect to GND. The positive voltage is supplied by the LM5002 circuit. The LM5002 circuit also provides a
UVLO function to remove the possibility of the LM3433 from drawing high currents at low input voltages during startup.
Initially the output current is set at the minimum of approximately 4A with the POT P1 fully counter-clockwise. To set the desired current level a short may be connected between LED + and LED-, then use a current probe and turn the POT clockwise until the desired current is reached. PWM dimming FETs are included on-board for testing when the LED can be connected directly next to the board. A shutdown test post on J2, ENA, is included so that startup and shutdown functions can be tested using an external voltage.


圖5.LM3433 評估板電路圖

評估板材料清單(BOM):



詳情請見:

http://www.national.com/ds/LM/LM3433.pdf?
和
http://www.national.com/an/AN/AN-1793.pdf