LM3404EVAL/NOPB National Semiconductor, LM3404EVAL/NOPB Datasheet - Page 2

• Manufacturer Part Number: LM3404EVAL/NOPB
• Description: BOARD EVALUATION LM3404
• Manufacturer: National Semiconductor
• Series: PowerWise®r

Specifications of LM3404EVAL/NOPB

• Current - Output / Channel: 1A
• Outputs And Type: 1, Non-Isolated
• Voltage - Output: 4 V
• Features: Dimmable
• Voltage - Input: 6 ~ 42 V
• Utilized Ic / Part: LM3404
• Silicon Manufacturer: National
• Silicon Core Number: LM3404
• Kit Application Type: Power Management - Voltage Regulator
• Application Sub Type: Buck Regulator
• Kit Contents: Board, User Guide, LM3404 Datasheet
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: *LM3404EVAL; LM3404EVAL

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The logic of DIM1 is direct, hence the LM3404/04HV will de-
liver regulated output current when the voltage at DIM1 is
high, and the current output is disabled when the voltage at
DIM1 is low. Connecting a constant logic low will disable the
output, and the LM3404/04HV is enabled if the DIM pin is
open-circuited. The DIM1 function disables only the power
MOSFET, leaving all other circuit blocks functioning to mini-
mize the converter response time.
The DIM2 terminal provides a second method for PWM dim-
ming by connecting to the gate of an optional MOSFET, 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 MOSFET can be
turned on and off much more quickly than the LM3404/04HV
can shutdown the internal MOSFET, providing faster re-
sponse time for higher frequency and/or greater resolution in
the PWM dimming signal. The trade-off 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 LM3404/04HV 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 LM3404/04HV.
Low Power Shutdown
The LM3404/04HV can be placed into a low power shutdown
(typically 90 µA) by grounding the OFF* terminal. During nor-
mal operation this terminal should be left open-circuit.
FIGURE 2. PWM Dimming Limits
2
Output Open Circuit
With either DIM terminal floating or connected to logic high,
the LM3404/04HV 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
(LM3404) or 100V (LM3404HV) 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
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 MOS-
FET in this case. The result is a low power hiccup mode,
designed to prevent excessive voltage at the output and ther-
mal stress on the inductor, internal MOSFET, and input volt-
age source.
Z
. In the case of an accidental open circuit at the
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