Texas Instruments LM3402MA (Mini SOIC) - 0.5A Constant Current Buck Regulator for HB LEDs (LM3402EVAL Board) LM3402EVAL/ LM3402EVAL/NOPB Datenbogen
Produktcode
LM3402EVAL/NOPB
GND
DIM
BOOT
SW
CS
RON
LM3402/02HV
VIN
D1
L1
C
B
R
SNS
C
F
R
ON
C
IN
V
IN
= 6V to 42V (LM3402)
V
IN
= 6V to 75V (LM3402HV)
VCC
C
O1
OFF
DIM1
LED
ANODE
ANODE
LED
CATHODE
CATHODE
1
2
3
4
5
6
7
8
(used in BOM 2 only)
Low Power Shutdown
The DIM2 terminal provides a second method for PWM dimming by connecting to the gate of an optional
NFET, Q1. Note that Q1 is not provided on the standard BOM, and must be added for the DIM2 function
to operate. Q1 provides a parallel path for the LED current. This small NFET can be turned on and off
much more quickly than the LM3402/02HV can shutdown the internal NFET, providing faster response
time for higher frequency and/or greater resolution in the PWM dimming signal. The tradeoff in this
method is that the full current flows through Q1 while the LED is off, resulting in lower efficiency.
NFET, Q1. Note that Q1 is not provided on the standard BOM, and must be added for the DIM2 function
to operate. Q1 provides a parallel path for the LED current. This small NFET can be turned on and off
much more quickly than the LM3402/02HV can shutdown the internal NFET, providing faster response
time for higher frequency and/or greater resolution in the PWM dimming signal. The tradeoff in this
method is that the full current flows through Q1 while the LED is off, resulting in lower efficiency.
The logic of DIM2 is inverted, hence the LM3402/02HV will deliver regulated output current when the
voltage at DIM2 is low, and the current output is disabled when the voltage at DIM2 is high. Connecting a
constant logic high to the DIM2 will turn off the LED but will not shut down the LM3402/02HV.
voltage at DIM2 is low, and the current output is disabled when the voltage at DIM2 is high. Connecting a
constant logic high to the DIM2 will turn off the LED but will not shut down the LM3402/02HV.
7
Low Power Shutdown
The LM3402/02HV can be placed into a low power shutdown (typically 90 µA) by grounding the OFF
terminal. During normal operation this terminal should be left open-circuit.
terminal. During normal operation this terminal should be left open-circuit.
8
Output Open Circuit
With either DIM terminal floating or connected to logic high, the LM3402/02HV will begin to operate as
soon as it has an input of at least 6V. In the case that the input is powered but no LED array is connected
the output voltage will rise to equal the input voltage. The output of the circuit is rated to 50V (LM3402) or
100V (LM3402HV) and will not suffer damage, however care should be taken not to connect an LED array
if the output voltage is higher than the target forward voltage of the LED array in steady state.
Alternatively, a zener diode and zener current limiting resistor can be placed in the positions Z1 and R
soon as it has an input of at least 6V. In the case that the input is powered but no LED array is connected
the output voltage will rise to equal the input voltage. The output of the circuit is rated to 50V (LM3402) or
100V (LM3402HV) and will not suffer damage, however care should be taken not to connect an LED array
if the output voltage is higher than the target forward voltage of the LED array in steady state.
Alternatively, a zener diode and zener current limiting resistor can be placed in the positions Z1 and R
Z
. In
the case of an accidental open circuit at the output Z1 will enter reverse bias and attempt to pull the CS
pin voltage up to the output voltage. An internal comparator monitors the CS pin voltage and will disable
the internal NFET in this case. The result is a low power hiccup mode, designed to prevent excessive
voltage at the output and thermal stress on the inductor, internal NFET, and input voltage source.
pin voltage up to the output voltage. An internal comparator monitors the CS pin voltage and will disable
the internal NFET in this case. The result is a low power hiccup mode, designed to prevent excessive
voltage at the output and thermal stress on the inductor, internal NFET, and input voltage source.
Figure 3. Standard Schematic
3
SNVA175C – September 2006 – Revised April 2013
AN-1500 LM3402/02HV Demo Board
Copyright © 2006–2013, Texas Instruments Incorporated