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NSLM3409PFET step-down control high-power LED driver solution

NS’s LM3409/09HV is a P-channel MOSFET (PFET) controller for step-down current regulation. The LM3409/LM3409Q input voltage is from 6V to 42V, and the LM3409HV/LM3409QHV input voltage is from 6V to 75V. The PWM dimming range is 10000:1, and the analog dimming range is 250:1. It supports all ceramic capacitor outputs and non-capacitor outputs. It can drive high-power LEDs with forward current up to 5A. It is mainly used in LED drivers.” title=”LED driver” >LED driver, constant current source, automotive lighting, general lighting and industrial lighting. This article introduces the LM3409/09HV main features, block diagram, various application circuits and corresponding bill of materials, as well as the LM3409HV evaluation board circuit diagram and evaluation board bill of materials.

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 main features:

■ 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 application:

■ LED Driver

■ Constant Current Source

■ Automotive Lighting

■ General Illumination

■ Industrial Lighting

figure 1. LM3409/09HV Block Diagram

figure 2. LM3409/09HV Typical Application Circuit Diagram

image 3. LM3409/09HV PWM dimming 10 LED driver circuit diagram
Figure 3 Bill of Materials:

Figure 4. LM3409/09HV Analog Dimming 4 LED Driver Circuit Diagram
Figure 4 Bill of Materials:

Figure 5. LM3409/09HV external parallel FET PWM dimming 10 LED driver circuit diagram
Figure 5 Bill of Materials:

Image 6. LM3409/09HV single potentiometer analog dimming 6 LED driver circuit diagram
Figure 6 Bill of Materials:

Figure 7. LM3409/09HV 75°C thermal foldback 16 LED driver circuit diagram
Figure 7 Bill of Materials:

Figure 8. LM3409/09HV high current 4 LED driver circuit diagram
Figure 8 Bill of Materials:

LM3409HV Evaluation Board

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.

Figure 9. LM3409HV Evaluation Board Outline Drawing

Figure 10. LM3409HV Evaluation Board Circuit Diagram
LM3409HV Evaluation Board Bill of Materials:

For details, see: