LM3401MM/NOPB National Semiconductor, LM3401MM/NOPB Datasheet - Page 6
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LM3401MM/NOPB
Manufacturer Part Number
LM3401MM/NOPB
Description
IC LED DRIVER HIGH BRIGHT 8-MSOP
Manufacturer
National Semiconductor
Series
PowerWise®r
Type
HBLED Driverr
Datasheet
1.LM3401MMNOPB.pdf
(18 pages)
Specifications of LM3401MM/NOPB
Constant Current
Yes
Topology
PWM, Step-Down (Buck)
Number Of Outputs
1
Internal Driver
No
Type - Primary
General Purpose
Type - Secondary
High Brightness LED (HBLED)
Frequency
1.5MHz
Voltage - Supply
4.5 V ~ 35 V
Mounting Type
Surface Mount
Package / Case
8-MSOP, Micro8™, 8-uMAX, 8-uSOP,
Operating Temperature
-40°C ~ 125°C
Current - Output / Channel
1A
Internal Switch(s)
Yes
Efficiency
92%
Operating Supply Voltage (typ)
5/9/12/15/18/24V
Number Of Segments
1
Operating Temperature (min)
-40C
Operating Temperature (max)
125C
Operating Temperature Classification
Automotive
Package Type
MSOP
Pin Count
8
Mounting
Surface Mount
Power Dissipation
660mW
Operating Supply Voltage (min)
4.5V
Operating Supply Voltage (max)
35V
For Use With
LM3401EVAL - BOARD EVALUATION FOR LM3401
Lead Free Status / RoHS Status
Lead free / RoHS Compliant
Voltage - Output
-
Lead Free Status / Rohs Status
Compliant
Other names
LM3401MMTR
Available stocks
Company
Part Number
Manufacturer
Quantity
Price
Part Number:
LM3401MM/NOPB
Manufacturer:
NS/国半
Quantity:
20 000
www.national.com
Block Diagram
Operational Description
HYSTERETIC CONTROL
The LM3401 is a step-down DC-DC controller designed to
provide a constant current source for driving a high power
LED string.
The LM3401 uses comparator-based voltage mode hysteretic
control for a simple and stable design. Hysteretic control does
not utilize an internal oscillator, but relies on output conditions
to directly control switching. The LM3401 controls LED cur-
rent within the adjustable hysteresis window by monitoring
peak and valley voltage at the SNS pin. A dual sided hystere-
sis window is used to optimize accuracy.
Regulated LED current flows to ground through a sense re-
sistor at the SNS pin. The voltage generated at the SNS pin
is compared to the 200 mV internal reference. When the SNS
voltage falls below the reference voltage minus hysteresis,
the output of the hysteretic comparator goes low. This results
in the driver output, HG, pulling the gate of the PFET low and
turning on the PFET.
With the PFET on, LED current ramps up through the PFET
and the inductor. As the LED current increases, the SNS volt-
age reaches its upper threshold (reference voltage plus hys-
teresis). This forces the output of the comparator and HG to
go high, which turns the PFET off. When the PFET turns off,
current flows through the catch diode, and LED and inductor
current ramp down. When the SNS voltage falls to its lower
threshold, the cycle repeats. The resulting LED current, SNS,
and switch node waveforms are shown in Figure 2.
FIGURE 1. Block Diagram
6
OUTPUT CURRENT SETTING
The LED average current is programmed using a resistor be-
tween SNS and GND, shown as R1 in the typical application
schematic. The SNS resistor (R
lows:
Where V
LED current.
The sense resistor power rating must be higher than its power
dissipation. The required power rating can be calculated (in
Watts) as follows:
FIGURE 2. Hysteretic Switching Waveforms
SNS
is 200 mV typically, and I
SNS
30021415
) can be calculated as fol-
LED
is the DC average
30021416