LM3414MR/NOPB National Semiconductor, LM3414MR/NOPB Datasheet - Page 13

• Manufacturer Part Number: LM3414MR/NOPB
• Description: IC LED DRIVER BUCK 1A 8-PSOP
• Manufacturer: National Semiconductor
• Series: PowerWise®r
• Type: Automotive, High Brightness (HBLED)r

Specifications of LM3414MR/NOPB

• Constant Current: Yes
• Topology: Low Side, PWM, Step-Down (Buck)
• Number Of Outputs: 1
• Internal Driver: Yes
• Type - Primary: Automotive, General Purpose
• Type - Secondary: High Brightness LED (HBLED)
• Frequency: 250kHz ~ 1MHz
• Voltage - Supply: 4.5 V ~ 42 V
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (0.154", 3.90mm Width) Exposed Pad
• Operating Temperature: -40°C ~ 125°C
• Current - Output / Channel: 1A
• Internal Switch(s): Yes
• Efficiency: 96%
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Voltage - Output: -

INDUCTOR SELECTION
To
LM3414/14HV must operate in Continuous Conduction Mode
(CCM). With the incorporation of PLM, the peak-to-peak in-
ductor current ripple can be set as high as ±60% of the defined
average output current. The minimum inductance of the in-
ductor is decided by the defined average LED current and
allowable inductor current ripple. The minimum inductance
can be found by the equations shown in below:
Since:
Thus:
The LM3414/14HV can maintain LED current regulation with-
out output filter capacitor. This is because the inductor of the
floating buck structure provides continuous current to the LED
throughout the entire switching cycle. When LEDs are driven
without filter capacitor, the LED peak current must not set ex-
ceeding the rated current of the LED. The peak LED current
is governed by the following equation:
INTERNAL N_MOS POWER SWITCH
The LM3414/14HV features an integrated N-channel power
MOSFET that connects between the LX and GND pins for
power switching. With the switch turned ON, the resistance
across the LX and GND pins is 1.8Ω maximum.
ensure
proper
output
FIGURE 3. Waveforms of a Floating Buck LED Driver with PLM
current
regulation,
the
13
INTERNAL VCC REGULATOR
The LM3414/14HV features a 5.4V internal voltage regulator
that connects between the VIN and VCC pins for powering
internal circuitry and provide biases to external components.
The VCC pin must be bypassed to the GND pin with a 1µF
ceramic capacitor, C
as possible. When the input voltage falls below 6V, the VCC
voltage will drop below 5.4V and decrease proportionally as
Vin decreases. The device will shutdown as the VCC voltage
falls below 3.9V. When the internal regulator is used to pro-
vide bias to external circuitry, it is essential to ensure the
current sinks from VCC pin does not exceed 2mA to maintain
correct voltage regulation.
CONTROL SCHEME
The main control circuitry of the LM3414/14HV is generally a
Pulse-Width-Modulated (PWM) controller with the incorpora-
tion of the Pulse-Level-Modulation (PLM) technology. PLM is
a technology that facilitates true output average current con-
trol without the need to sense the output current directly. In
the LM3414/LM3414HV, the PLM circuit senses the current
of the internal switch through an integrated current sensing
circuitry to realize average output current control. The use of
PLM reduces the power losses on current sensor as it needs
current information only when the switch is turned ON.
In general, the LED drivers with current sensing resistor at the
output, the power dissipation on the current sensing resistor
is I
R
LM3414/LM3414HV, because of the incorporation of PLM,
power dissipates on the R
power switch. The power loss on R
R
when the switching duty cycle, D of a converter is 0.5, the
power loss on R
tional output current sensing.
ISNS
ISNS
LED
2
x D, where D is the switching duty cycle. For example,
is the resistance of the current sensing resistor. In the
x R
ISNS
, where I
ISNS
VCC
with PLM is half of those with conven-
LED
that connected to the pins as close
ISNS
is the average output current and
only in ON period of the internal
ISNS
becomes I
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LED
2
x