Texas Instruments LM3434 Evaluation Board LM3434SQ-20AEV/NOPB LM3434SQ-20AEV/NOPB 用户手册
产品代码
LM3434SQ-20AEV/NOPB
User's Guide
SNVA431B – March 2010 – Revised May 2013
AN-2041 LM3434 20A Evaluation Board
1
Introduction
The LM3434 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 -30V 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.
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 -30V 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
LM3434 Board Description
The evaluation board is designed to provide a constant current in the range of 4A to 20A. The LM3434
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 -9V to -30V 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 LM3434 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. The current may
be adjusted with P1 up to 18A. 20A output may be achieved either by bypassing P1 and applying an
analog voltage directly to ADJ or by adjusting the values of R1 and/or R2 to get higher than 1.5V with P1
fully clockwise. 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 -9V to -30V 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 LM3434 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. The current may
be adjusted with P1 up to 18A. 20A output may be achieved either by bypassing P1 and applying an
analog voltage directly to ADJ or by adjusting the values of R1 and/or R2 to get higher than 1.5V with P1
fully clockwise. 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 LM3434 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 with respect to 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 with respect to GND to adjust the
voltage across the sense resistor (R
SENSE
) R15. The shunt may also be removed and an external voltage
positive with respect to GND can then be applied to the ADJ test point on the board. A 5M
Ω
resistor (two
10M
Ω
resistors in parallel) comes mounted on the board so using the V
SENSE
vs. V
ADJ
graph in
the current can be set using the following equation:
I
LED
= V
SENSE
/R
SENSE
(1)
Alternatively the shunt can be removed and the ADJ test point can be connected to the VINX test point to
fix V
fix V
SENSE
at 60mV.
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1
SNVA431B – March 2010 – Revised May 2013
AN-2041 LM3434 20A Evaluation Board
Copyright © 2010–2013, Texas Instruments Incorporated