Texas Instruments LM3406 - 1.5A Constant Current Buck Regulator Evaluation Board for Driving High Power LEDs LM3406MHEVA LM3406MHEVAL/NOPB 데이터 시트
제품 코드
LM3406MHEVAL/NOPB
C5535676
Connector
Connector
P6
P1
Anode of
First LED
Cathode of
Last LED
Setting the LED Current
Figure 3. 6-Pin LED Connector, J1
4
Setting the LED Current
The default forward current I
F
delivered to the LED array when no program jumper is installed on J2 is
0.35A, set by resistor R.35. The higher LED currents are set when the program jumper puts resistors R.7,
R1 or R1.5 in parallel with R.35. For users that wish to program a current other than one of the four
default levels, or for users who want the best accuracy at a given current, the program jumper J2 should
be removed, and R.35 changed according to the following equation:
R1 or R1.5 in parallel with R.35. For users that wish to program a current other than one of the four
default levels, or for users who want the best accuracy at a given current, the program jumper J2 should
be removed, and R.35 changed according to the following equation:
R.35 = 0.2 / I
F
(3)
This resistor should be rated to handle the power dissipation of the LED current. For example, the closest
5% tolerance resistor to set an LED current of 0.35A is 0.56
5% tolerance resistor to set an LED current of 0.35A is 0.56
Ω
. In steady state this resistor will dissipate
(0.35
2
x 0.56) = 69 mW, indicating that a resistor with a 1/8W rating is more than capable of dissipating
the power.
5
Pulse Width Modulation (PWM) Dimming
The DIM1 terminal on the PCB provides an input for a logic-level pulse width modulation signal for
dimming of the LED array. In order to fully enable and disable the LM3406 the PWM signal should have a
maximum logic low level of 0.8V and a minimum logic high level of 2.2V. Graphical representations of
minimum and maximum PWM duty cycle are illustrated in
dimming of the LED array. In order to fully enable and disable the LM3406 the PWM signal should have a
maximum logic low level of 0.8V and a minimum logic high level of 2.2V. Graphical representations of
minimum and maximum PWM duty cycle are illustrated in
. The interval t
D
represents the delay
from a logic high at the DIM pin to the rise in output current. The quantities t
SU
and t
SD
represent the time
needed for the output current to slew up to steady state and slew down to zero, respectively. It is
important to note that t
important to note that t
D
is a property of the LM3406 and remains fixed in all applications. The slew rates
t
SU
and t
SD
are a function of the external circuit parameters V
IN
, V
O
, I
F
, inductance (L) and the LM3406
parameter t
OFF-MIN
. Response times for a circuit driving three white LEDs at 1A from 24V are shown in the
Typical Performance Characteristics section, but the user should test every new circuit to determine the
actual PWM dimming response.
actual PWM dimming response.
3
SNVA300A – September 2008 – Revised May 2013
AN-1750 LM3406 Evaluation Board
Copyright © 2008–2013, Texas Instruments Incorporated