LM3492 Datasheet, PDF (1/8 Pages) National Semiconductor (TI) – Evaluation Board Reference Design integrates a boost converter

LM3492 Evaluation Board
Reference Design
National Semiconductor
Application Note 2056
L.K. Wong
September 21, 2010
Introduction
The LM3492 integrates a boost converter and a two-channel
current regulator to implement a high efficient and cost effec-
tive 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 Pro-
jected-On-Time control method to give a fast transient re-
sponse 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 tun-
ing, 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 eTSSOP-20 package.
This application note details the design of a LM3492 evalua-
tion board which 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 shown. Typical performance
and operating waveforms are also provided for reference.
Evaluation Board Schematic and PCB Layout
FIGURE 1. LM3492 Evaluation Board Schematic
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