LM3430_07 Datasheet, PDF (1/16 Pages) National Semiconductor (TI) – LED Backlighting Solution with LM3430 and LM3432

LED Backlighting Solution
with LM3430 and LM3432
National Semiconductor
Application Note 1679
TK Man
September 2007
Introduction
Since the release of high brightness White LED (HB-WLED)
in the middle of 1990's, tremendous research efforts have
been undergoing to improve the emission efficiency, reliability
and thermal packaging technologies in order to expand its
range of applications. In the last few years, improvements in
HB-WLED performance and price structure attracts more po-
tential applications considering this new lighting source tech-
nology as an alternative to conventional one. One area of
applications, LCD display backlighting, consider this new
backlighting method as the ultimate solution to replace the
existing Cold Cathode Fluorescent Lamps (CCFL). Backlight
LED-driver solutions need to exhibit following characteristics:
• Instead of voltage control, LED-driver need direct LED
current control to ensure consistent color and brightness;
• High conversion efficiency under various conditions;
• Support PWM dimming;
• Limit LED's rail voltage while LEDs open circuited;
• Ability to shutdown individual channel(s) when short or
open circuited LED(s) detected;
• Device over temperature detect and shutdown;
• Low profile, small size and ease to use.
The LM3432 is a 6-channel high voltage current regulator
which provides a simple solution for LED backlighting appli-
cations and the LM3430 is a companion device to supply high
voltage required to drive serially connected LED strings. The
LM3430 and the LM3432 provide a complete solution to most
HB-WLED backlighting applications for notebook and PC
monitor. In this application note, a typical example for a solu-
tion to drive six strings of twelve LEDs in series running at
20mA per string is described in details.
The Demonstration Board
The LM3432 is used to drive 6-channel LED strings with 12
LEDs in series per string running at 20mA. This example pro-
vides a simple solution for HB-WLED backlight applications
in notebooks and monitors. The LM3432 is powered with its
companion device, LM3430, the Dynamic Headroom Control
(DHC) feature helps to provide the optimal system efficiency.
The design specification for this demonstration board is
shown in below:
Design Specifications:
• Supply Voltage, VIN
6V to 21V
• Boost Converter Switching Frequency, F_SW
• Boost Converter Output Voltage, V_LED
(With load disconnected)
1 MHz
50V
• Number of LED String
6
• Number of LED per String
12
• LED Current per String, I_LED
PWM Dimming Function:
20 mA
• Analog Dimming Mode
Control Voltage Input, V_PWM
Dimming Frequency, F_PWM
• Digital Dimming Mode
1V to 3V (0% to 100%)
≊23 kHz
External PWM Signal 20 kHz to 25 kHz, 2.5V_peak
© 2007 National Semiconductor Corporation 300289
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