Texas Instruments LM3433 Evaluation Board LM3433SQ-14AEV/NOPB LM3433SQ-14AEV/NOPB 用户手册
产品代码
LM3433SQ-14AEV/NOPB
User's Guide
SNVA327B – March 2008 – Revised May 2013
AN-1793 LM3433 4A to 20A 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 LEDs (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 w.r.t. 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.
high brightness LEDs (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 w.r.t. 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 Board Description
The evaluation board is designed to provide a constant current in the range of 4A to 20A. 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.
The positive voltage is supplied by the LM5002 circuit. The LM5002 circuit also provides a UVLO function
to remove the possibility of the LM3433 from drawing high currents at low input voltages during startup.
Initially the output current is set at the minimum of approximately 4A 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.
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.
The positive voltage is supplied by the LM5002 circuit. The LM5002 circuit also provides a UVLO function
to remove the possibility of the LM3433 from drawing high currents at low input voltages during startup.
Initially the output current is set at the minimum of approximately 4A 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.
3
Setting the LED Current
The LM3433 evaluation board is designed so that the LED current can be set in multiple ways. There is a
shunt on J2 initially connecting the ADJ pin to the POT allowing the current to be adjusted using the POT
P1. This POT will apply a voltage to the ADJ pin between 0.3V and 1.5V w.r.t. GND to adjust the voltage
across the sense resistor (R
shunt on J2 initially connecting the ADJ pin to the POT allowing the current to be adjusted using the POT
P1. This POT will apply a voltage to the ADJ pin between 0.3V and 1.5V w.r.t. GND to adjust the voltage
across the sense resistor (R
SENSE
) R15. The shunt may also be removed and an external voltage positive
w.r.t. GND can then be applied to the ADJ test point on the board. A 5m
Ω
resistor comes mounted on the
board so using the V
SENSE
vs. V
ADJ
graph in the
section the current can be set using
I
LED
= V
SENSE
/R
SENSE
(1)
Alternatively the shunt can be removed and connect the ADJ test point can be connected to the VINX test
point to fix V
point to fix V
SENSE
at 60mV.
4
PWM Dimming
The LM3433 is capable if high speed PWM dimming in excess of 40kHz. Dimming is accomplished by
shorting across the LED with a FET(s). Dimming FETs are included on the evaluation board for testing
LEDs placed close to the board. The FETs on the evaluation board should be removed if using dimming
FETs remotely placed close to the LED (recommended).
shorting across the LED with a FET(s). Dimming FETs are included on the evaluation board for testing
LEDs placed close to the board. The FETs on the evaluation board should be removed if using dimming
FETs remotely placed close to the LED (recommended).
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1
SNVA327B – March 2008 – Revised May 2013
AN-1793 LM3433 4A to 20A LED Driver Evaluation Board
Copyright © 2008–2013, Texas Instruments Incorporated