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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