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User's Guide
SNVA386D–March 2009–Revised May 2013
AN-1937 LM3433 10A to 40A LED Driver Evaluation Board
1 Introduction
The LM3433 is an adaptive constant on-time DC/DC buck constant current controller designed to drive a
high brightness LED (HB LED) at high forward currents. It is a true current source that provides a constant
current with constant ripple current regardless of the LED forward voltage drop. The board can accept an
input voltage ranging from -9V to -14V with respect to GND. The output configuration allows the anodes of
multiple LEDs to be tied directly to the ground referenced chassis for maximum heat sink efficacy when a
negative input voltage is used.
2 LM3433 High Current Board Description
The evaluation board is designed to provide a constant current in the range of 10A to 60A (although the
board is thermally limited to approximately 40A continuous operation) and can connect directly to a
Luminus Devices, Inc. PhlatLight
®
PT-120 or similar high current LED. It is ideal for pulsing an LED at 30A
or greater for applications such as rear and forward projection. The LM3433 requires two input voltages
for operation. A positive voltage with respect to GND is required for the bias and control circuitry and a
negative voltage with respect to GND is required for the main power input. This allows for the capability of
using common anode LEDs so that the anodes can be tied to the ground referenced chassis. The
evaluation board only requires one input voltage of -12V with respect to GND (any high current 12V supply
will work). The positive voltage with respect to GND on the board is supplied by the LM5002 circuit (see
below). Initially the output current is set at the minimum of approximately 10A with the POT P1 fully
counter-clockwise. To set the desired current level a short may be connected between LED+ and LED-,
then use a current probe and turn the POT clockwise until the desired current is reached. PWM dimming
FETs are included on-board for testing when the LED can be connected directly next to the board. A
shutdown test post on J2, ENA, is included so that startup and shutdown functions can be tested using an
external voltage. Note that the test points for GND and -12V are for measurement only, the high current
input source should be connected through J1.
3 LM5002 Circuit
The positive voltage with respect to GND on the board is supplied by the LM5002 circuit. The LM5002
feedback is level shifted so that the output that supplies the LM3433 bias circuitry will remain at +5V with
respect to GND regardless of where VEE is in the -9V to -14V range. The LM5002 circuit also provides a
UVLO function to remove the possibility of the LM3433 drawing high currents at input voltages less than -
9V during startup. This circuit was designed with enough output current to power a small 5V sideblower
fan (Sunon part number B0502AFB2-8) to help keep the inductor, and therefore the board to some
degree, cooler if extreme ambient temperatures are expected. One LM5002 circuit can supply enough
current to drive the positive voltage for multiple LM3433 circuits in a system, up to approximately 100.
PowerPAD is a trademark of Texas Instruments.
PhlatLight is a registered trademark of Luminus Devices, Inc.
All other trademarks are the property of their respective owners.
1
SNVA386D–March 2009–Revised May 2013 AN-1937 LM3433 10A to 40A LED Driver Evaluation Board
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Verzeichnis
- ・ Blockdiagramm on Seite 4
- ・ Anwendungsbereich on Seite 12
- ・ Elektrische Spezifikation on Seite 7
