Datasheet

User's Guide
SNVA438B–September 2010–Revised April 2013
AN-2056 LM3492 Evaluation Board Reference Design
1 Introduction
The LM3492 integrates a boost converter and a two-channel current regulator to implement a high
efficient and cost effective LED driver for driving two individually dimmable LED strings with a maximum
power of 15W and an output voltage of up to 65V. The boost converter employs a proprietary Projected-
On-Time control method to give a fast transient response with no compensation required, and a nearly
constant switching frequency programmable from 200 kHz to 1 MHz. The application circuit is stable with
ceramic capacitors and produces no audible noise on dimming. The programmable peak current limit and
soft-start features reduce current surges at startup, and an integrated 190 mΩ, 3.9A N-Channel MOSFET
switch minimizes the solution size. The fast slew rate current regulator allows high frequency and narrow
pulse width dimming signals to achieve a very high contrast ratio of 1000:1 at a dimming frequency of
more than 3 kHz. The LED current is programmable from 50 mA to 200 mA by a single resistor.
To maximize the efficiency, Dynamic Headroom Control (DHC) automatically adjusts the output voltage to
a minimum. DHC also facilitates a single BOM for different number of LED in a string, which is required for
backlight panels of different size, thereby reducing overall development time and cost. The LM3492 comes
with a versatile COMM pin which serves as a bi-directional I/O pin interfacing with an external MCU for the
following functions: power-good, over-temperature, IOUT over- and under-voltage indications, switching
frequency tuning, and channel 1 disabling. Other supervisory functions of the LM3492 include precise
enable, VCC under-voltage lock-out, current regulator Over-Power protection, and thermal shutdown
protection. The LM3492 is available in the thermally enhanced HTSSOP-20 package.
This user's guide details the design of a LM3492 evaluation board that drives 2 LED strings, each of which
consists of 10 LEDs running at 150 mA and the forward voltage of each LED is typically 3.8V. The input
voltage is from 9V to 16V. The evaluation board schematic, PCB layout, Bill of Materials, and circuit
design descriptions are included. Typical performance and operating waveforms are also provided for
reference.
Table 1. Evaluation Board Performance Characteristic
Description Symbol Condition Min Typ Max Unit
Input Voltage V
IN
9 12 16 V
Rail Voltage V
OUT
39 V
LED Current I
LED
150 mA
LED Current ΔI
LED
ALL V
IN
-3 +3 %
Regulationt conditions
Efficiency V
IN
= 9V 85.7 %
V
IN
= 12V 88.2 %
V
IN
= 16V 89.1 %
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SNVA438B–September 2010–Revised April 2013 AN-2056 LM3492 Evaluation Board Reference Design
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