LM3421_11 Datasheet, PDF (1/20 Pages) National Semiconductor (TI) – LM3421 SEPIC LED Driver Evaluation Board for Automotive Applications

LM3421 SEPIC LED Driver
Evaluation Board for
Automotive Applications
National Semiconductor
Application Note 2009
Steve Solanyk
February 4, 2011
Introduction
This application note describes an evaluation board consist-
ing of the LM3421 controller configured as a SEPIC constant
current LED driver. It is capable of converting input voltages
from 8V to 18V and illuminating up to six LEDs with approxi-
mately 350mA of drive current.
Additional features include analog and pulse-width modulated
(PWM) dimming, over-voltage protection, under-voltage lock-
out and cycle-by-cycle current limit.
A bill of materials is included that describes the parts used in
this evaluation board. A schematic and layout have also been
included along with measured performance characteristics.
Performance Specifications
Key Features
• Designed to CISPR-25, Class 3 limits
• 0 to 10V analog dimming function
• PWM dimming function
• Input under-voltage protection
• Over-voltage protection
• Cycle-by-cycle current limit
• NoPB and RoHS compliant bill of materials
Applications
• Emergency lighting modules
• LED light-bars, beacons and strobe lights
• Automotive tail-light modules
Based on an LED V_f = 3.15V
Symbol Parameter
Min
V_IN
Operating Input Supply Voltage
8
V_IN(MAX) Input Supply Voltage Surge Voltage
-
V_OUT
LED String Voltage
-
I_LED
LED String Average Current
-
-
Efficiency (V_IN=12V, I_LED=345mA, 6 LEDs)
-
f_SW
Switching Frequency
-
-
LED Current Regulation
-
I_LIMIT
Current Limit
-
V_UVLO
Input Undervoltage Lock-out Threshold (V_IN Rising)
-
V_UVLO(HYS) Input Undervoltage Lock-out Hysteresis
-
V_OVP
Output Over-Voltage Protection Threshold
-
V_OVP(HYS) Output Over-Voltage Protection Hysteresis
-
Typ
12
50 V
18.9V (6 LEDs)
345 mA
85.4%
132 kHz
< 1% Variation
2.5 A
7.2V
1V
37 V
3.5 V
Max
18
-
-
-
-
-
-
-
-
-
Demo Board
© 2011 National Semiconductor Corporation 301075
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