Texas Instruments AN-1907 LM3423 User Manual

AN-1907 LM3423 Buck-Boost Configuration Evaluation
1 Introduction
This evaluation board has been designed to demonstrate the LM3423 low-side controller as a step-
up/step-down (buck-boost) regulator to deliver constant current to high power LEDs. A complete circuit
schematic and bill of materials for the evaluation board are included at the end of this document. The
printed circuit board consists of two layers of two ounce copper on FR4 material. The LM3423 evaluation
board is designed so that all options available can be evaluated and tested. Most applications will only
require a few options therefore jumpers can be placed, or removed as needed. A schematic of the full
featured LM3423 evaluation board and its bill of materials is provided in this document. Simplified design
examples with schematics and a bill of materials follow.
2 Device Description
The LM3423 is a high voltage, low-side NFET controller with an adjustable output current sense voltage.
Output voltage regulation is based on peak current-mode control, which eases the design of loop
compensation while providing inherent input voltage feed-forward compensation. The LM3423 includes a
high-voltage start-up regulator that operates over a wide input range of 4.5V to 75V. The PWM controller
is designed for high speed capability including a switching frequency range to 2.0 MHz. Additional features
include "zero" current shutdown, error amplifier, precision reference, logic-compatible DIM input suitable
for fast PWM dimming of the output, cycle-by-cycle current limit, LED ready flag, fault flag, programmable
fault timer, and thermal shutdown.
Standard Evaluation Board Operating Configuration
• f = 600 kHz
SW
• Over-voltage protection set at 56V
• V range 4.5V to 35V
IN
• Low side PWM fast dimming
• 2 to 8 series connected LEDs (V
• UVLO set at 8.4V
• I = 1A
LED
Available features that can be configured on the standard evaluation board by the user for are listed
below:
• Fixed or programmable LED current
• High-speed PWM high-side or low-side dimming
• User programmable over-voltage protection (OVP)
• Under-voltage lock-out (UVLO) protection
• Fault protection
• Soft-start
• Hysteretic current-mode control
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SNVA376A – December 2008 – Revised May 2013
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AN-1907 LM3423 Buck-Boost Configuration Evaluation Board
Copyright © 2008–2013, Texas Instruments Incorporated
SNVA376A – December 2008 – Revised May 2013
User's Guide
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