NS LM3409 PFET降压控制大功率LED驱动方案

发布时间：2011-6-20 12:51 发布者：Liming

关键词： LED驱动 , LM3409 , NS , PFET

NS 公司的LM3409/09HV是用于降压电流调整的P沟MOSFET（ PFET）控制器，LM3409/LM3409Q输入电压从6V到42V，LM3409HV/LM3409QHV输入电压从6V到75V。PWM调光范围10000:1，模拟调光范围250:1，支持所有的陶瓷电容输出和无电容输出能驱动正向电流达5A的大功率LED，主要用在LED驱动器，恒流源，汽车照明，通用照明和工业照明。本文介绍了LM3409/09HV主要特性，方框图，多种应用电路和相应的材料清单，以及LM3409HV评估板电路图和评估板材料清单。

PFET Buck Controller for High Power LED Drivers

The LM3409/09HV are P-channel MosFET (PFET) controllers for step-down (buck) current regulators. They offer wide input voltage range, high-side differential current sense
with low adjustable threshold voltage, fast output enable/disable function and a thermally enhanced eMSOP-10 package.

These features combine to make the LM3409/09HV ideal for use as constant current sources for driving LEDs where forward currents up to 5A are easily achievable.

The LM3409/09Q/09HV/09QHV uses Constant Off-Time (COFT) control to regulate an accurate constant current without the need for external control loop compensation. Analog and PWM dimming are easy to implement and result in a highly linear dimming range with excellent achievable contrast ratios.

Programmable UVLO, low-power shutdown, and thermal shutdown complete the feature set.

LM3409/09HV主要特性：

■ LM3409Q/LM3409QHV is an Automotive Grade product that is AEC-Q100 grade 1 qualified

■ 2Ω, 1A Peak MosFET Gate Drive

■ VIN Range: 6V to 42V (LM3409/LM3409Q)

■ VIN Range: 6V to 75V (LM3409HV/LM3409QHV)

■ Differential, High-side Current Sense

■ Cycle-by-Cycle Current Limit

■ No Control Loop Compensation Required

■ 10,000:1 PWM Dimming Range

■ 250:1 Analog Dimming Range

■ Supports All-Ceramic Output Capacitors and Capacitorless Outputs

■ Low Power Shutdown

■ Thermal Shutdown Protection

■ Thermally Enhanced eMSOP-10 Package

LM3409/09HV应用：

■ LED Driver

■ Constant Current Source

■ Automotive Lighting

■ General Illumination

■ Industrial Lighting

图1。LM3409/09HV方框图

图2。LM3409/09HV典型应用电路图

图3。LM3409/09HV PWM调光10个LED驱动电路图
图3材料清单：

图4。LM3409/09HV 模拟调光4个LED驱动电路图
图4材料清单：

图5。LM3409/09HV 外接并联FET PWM调光10个LED驱动电路图
图5材料清单：

图6。LM3409/09HV 单个电位计模拟调光6个LED驱动电路图
图6材料清单：

图7。LM3409/09HV 75度C热折返16个LED驱动电路图
图7材料清单：

图8。LM3409/09HV 大电流4个LED驱动电路图
图8材料清单：

LM3409HV评估板

This evaluation board showcases the LM3409HV PFET controller for a buck current regulator. It is designed to drive 12 LEDs (VO = 42V) at a maximum average LED current (ILED = 1.5A) from a DC input voltage (VIN = 48V). The switching frequency (fSW = 400 kHz) is targeted for the nominal operating point, however fSW varies across the entire operating range.

The circuit can accept an input voltage of 6V-75V. However, if the input voltage drops below the regulated LED string voltage, the converter goes into dropout and VO = VIN ideally. The PCB is made using 4 layers of 2 oz. copper with FR4 dieletric. The evaluation board showcases all features of the LM3409HV including analog dimming using the IADJ pin and internal PWM dimming using the EN pin. High frequency external parallel FET shunt PWM dimming can also be evaluated.

The board has a header (J1) with a removable jumper, which is used to select the PWM dimming method. The evaluation board has a right angle connector (J2) which can mate with an external LED load board allowing for the LEDs to be mounted close to the driver. This reduces potential ringing when there is no output capacitor. Alternatively, the LED+ and LED- turrets can be used to connect the LED load.

This board can be easily modified to demonstrate other operating points as shown in the Alternate Designs section. The LM3409/09HV datasheet Design Procedure can be used to design for any set of specifications.

Since the board contains a buck regulator designed for 48V input, the efficiency is very high at input voltages near or less than 48V. The switching frequency increases as input voltage increases, yielding lower efficiency at higher input voltages.

Note that increasing the off-time resistor (R6) will increase the efficiency at high input voltage.