LM3434主要特性 DLP投映仪RGB LED驱动器介绍

TI公司的LM3434是DC/DC降压控制器,为大功率LED照明提供恒定电流,工作输入电压-9V到-30V,输出电流6A, M频率大于30kHz,主要用在投映系统,固态照明和汽车照明.本文介绍了LM3434主要特性,框图,输出10A和20A应用电路,LM3434 20A评估板主要特性,电路图,材料清单和PCB设计图,以及采用LM3434的180W DLP投映仪RGB LED驱动器参考设计主要参数,电路图,材料清单和PCB设计图.

The LM3434 is an adaptive constant on-time DC/DC buck (step-down) constant current controller (a true current source). The LM3434 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 LM3434 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 LM3434 is available in a low profile 24-pin WQFN package.

LM3434主要特性:

Operating Input Voltage Range of –9V to -30V 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 Efficiency
No Output Capacitor Required
Up to 1MHz Switching Frequency
Low IQ, 1mA Typical
Soft Start
Adaptive Programmable ON Time Allows for Constant Ripple Current
24-Pin WQFN Package

LM3434应用:

Projection Systems
Solid State Lighting
Automotive Lighting

图1. LM3434框图

图2. LM3434典型应用电路

图3. LM3434输出10A的应用电路

图4. LM3434输出20A的应用电路

LM3434 20A 评估板

The evaluation board is designed to provide a constant current in the range of 4A to 20A. The LM3434 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 -9V to -30V 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 LM3434 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. The current may be adjusted with P1 up to 18A. 20A output may be achieved either by bypassing P1 and applying an analog voltage directly to ADJ or by adjusting the values of R1 and/or R2 to get higher than 1.5V with P1 fully clockwise. 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.
 

图5. LM3434 20A 评估板电路图

LM3434 20A 评估板材料清单:

图6. LM3434 20A 评估板PCB顶层元件布局图

图7. LM3434 20A 评估板PCB底层元件布局图

180W DLP投映仪RGB LED驱动器

The PMP4356 is RGB LED drivers solution which used in high power density DLP projector. LM3434 and power block CSD87350 are used in each rail to provide up to 15A of drive ability. The design demostrates high efficiency up to  92.5%@full load within the form factor of 80mm*45mm*10.8mm with good dimming performance.