LM3404MA National Semiconductor, LM3404MA Datasheet - Page 19

• Manufacturer Part Number: LM3404MA
• Description: DRIVER, LED, 1A, POWERWISE, SO-8, 3404
• Manufacturer: National Semiconductor

Specifications of LM3404MA

• Led Driver Application: Automotive, Industrial Lighting
• No. Of Outputs: 1
• Output Current: 1.2A
• Output Voltage: 40V
• Input Voltage: 6V To 42V
• Dimming Control Type: PWM
• Operating: RoHS Compliant
• Topology: Buck

GENERAL COMMENTS REGARDING OTHER PINS
Any pin that goes “off-board” through a connector should have
series resistance of at least 1kΩ to 10kΩ in series with it to
protect it from ESD or other transients. These series resistors
limit the peak current that can flow (or cause a voltage drop)
during a transient event, thus protecting the pin and the de-
vice. Pins that are not used should not be left floating. They
should instead be tied to GND or to an appropriate voltage
through resistance.
Design Example 1: LM3404
The first example circuit will guide the user through compo-
nent selection for an architectural accent lighting application.
A regulated DC voltage input of 24V ±10% will power a 5.4W
FIGURE 11. VIN Pin with Additional Input Protection
FIGURE 12. Schematic for Design Example 1
19
"warm white" LED module that consists of four LEDs in a 2 x
2 series-parallel configuration. The module will be treated as
a two-terminal element and driven with a forward current of
700 mA ±5%. The typical forward voltage of the LED module
in thermal steady state is 6.9V, hence the average output
voltage will be 7.1V. The objective of this application is to
place the complete current regulator and LED module in a
compact space formerly occupied by a halogen light source.
(The LED will be on a separate metal-core PCB and heatsink.)
Switching frequency will be 400 kHz to keep switching loss
low, as the confined space with no air-flow requires a maxi-
mum temperature rise of 50°C in each circuit component. A
small solution size is also important, as the regulator must fit
on a circular PCB with a 1.5" diameter. A complete bill of ma-
terials can be found in
Table 1
at the end of this datasheet.
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