Texas Instruments Incorporated LM3407 Application Note
LM3407
Application Note 1763 LM3407 Evaluation Board Reference Design
Literature Number: SNVA308A
LM3407 Evaluation Board Reference Design AN-1763
LM3407 Evaluation Board
Reference Design
Introduction
The LM3407 is a Pulse-Width-Modulation (PWM) floating
buck converter with an integrated N-channel power MOSFET
designed to provide precision constant current output for driving high power LEDs, such as the Lumileds Luxeon® power
LEDs and OSRAM Golden DRAGON® LEDs. The switching
frequency is selectable between 300 kHz and 1 MHz by
changing the value of the frequency setting resistor, allowing
for the use of small external components. The LM3407 features a Pulse Level Modulation (PLM) control scheme which
ensures the accuracy of the constant current output well within 10% over input voltage and operating temperature ranges
Evaluation Board Schematic
National Semiconductor
Application Note 1763
SH Wong
January 21, 2009
with an external 1% thick film current setting resistor. The
converter features a DIM pin which accepts standard logic
pulses for controlling the brightness of the LED array, making
the LM3407 ideal for use as a precision power LED driver or
constant current source.
This application note introduces the design of a sample circuit
with the LM3407 providing 350 mA constant current to drive
an LED array of 6 high power LEDs connected in series. The
board can accept an input voltage ranging from 22V to 30V.
The schematic, PCB layout, bill of materials, and circuit design criteria are shown in detail. Typical performance and
operating waveforms are also provided for reference.
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FIGURE 1. LM3407 Evaluation Board Schematic
© 2009 National Semiconductor Corporation 300467 www.national.com
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FIGURE 2. LM3407 Evaluation Board PCB Top Overlay
FIGURE 3. LM3407 Evaluation Board PCB Top View
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FIGURE 4. LM3407 Evaluation Board PCB Bottom View
Evaluation Board Quick Setup Procedures
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Step Procedure Notes
1 Remove all jumpers on the evaluation board.
2 Connect the LED array of 6 power LEDs to J1.
3 Connect Power Supply output to the VIN terminal of the
evaluation board.
4 Set the power supply output voltage to 24V. VIN should not exceed 30V
6 Check the voltage of the VCC terminal of the board. VCC = 4.5V ± 8%
7 Short pin 1 and 2 of J3 by using a jumper. LEDs fully turned ON
8 Check the LED current (I
9 Short J2 by using a jumper to check the shutdown function. I
) by using an ammeter. I
OUT
= 350mA ± 6%
OUT
= 0
OUT
Evaluation Board Performance Characteristic
Description Symbol Condition Min Typ Max Unit
Input Voltage V
Output Current I
Output Current
|ΔI
OUT
OUT
IN
DIM pin connected to VCC 330 350 370 mA
|
All VIN and I
Variation
Efficiency No. of LED = 6 93 96 %
No. of LED = 4 90 95 %
No. of LED = 2 85 92 %
22 24 30 V
Conditions 6 %
OUT
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