LM3464 Datasheet, PDF (1/14 Pages) National Semiconductor (TI) – 4 Channel LED Driver Evaluation Board

LM3464 4 Channel LED
Driver Evaluation Board
National Semiconductor
Application Note 2071
SH Wong
August 20, 2010
Introduction
The LM3464 is a linear LED driver with Dynamic Headroom
Control (DHC) technology designed to drive four serial high
power / high brightness LED strings. Four individual linear
current regulators with low-side N-channel MOSFETs realize
regulations of LED currents. The DHC optimizes system effi-
ciency automatically while maintaining stable and accurate
LED currents. The LM3464 includes a voltage regulator for
powering the internal circuits that operates over wide input
range of 12V to 80V, eases the design of driver stage for dif-
ferent source voltage. The Thermal foldback feature is de-
signed to prolong the lifetime of the LEDs by reducing the
average LED current for applications with high ambient tem-
perature. The LM3464 features a fault handling circuit that
avoids system failure due to accidentally short or open circuit
of LED strings. Two or more LM3464 can be cascaded to ex-
pand the number of output channels, enabling flexible system
architectural design.
This evaluation board demonstrates the system efficiency
and LED current regulation accuracy of the LM3464 LED
driver typical application circuit as a 50W LED lighting system.
The schematic, bill of material and PCB layout for the evalu-
ation board are provided in this document. The evaluation
board can adapt to different types of primary power supplies
with changes of value of a few components only.
Standard Settings of the Evaluation
Board
• Vin range 12V to 80V
• 48V LED turn ON voltage
• 350mA LED current per channel
• 2kHz thermal foldback dimming frequency
As the LED turn-on voltage of the LM3464 evaluation board
is designed to 48V, it is recommended to set the supply volt-
age to the evaluation board no more than 60V to avoid high
power dissipation on the MOSFETs of the low-side current
regulators upon system startup. For driving different number
of LEDs, the startup voltage will need to be adjusted by
changing the value of the resistors RFB1 and RFB2.
Highlight Features
• Dynamic Headroom Control (DHC)
• Thermal foldback control
• High speed PWM dimming
• Minimum brightness limit for thermal foldback control
• Cascade operation for output channel expansion
• Vin Under-Voltage-Lockout
• Fault protection and indication
• Programmable startup voltage
• Thermal Shutdown
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