LM3402MRX National Semiconductor, LM3402MRX Datasheet - Page 20

• Manufacturer Part Number: LM3402MRX
• Description: LM3402/LM3402HV 0.5A Constant Current Buck Regulator for Driving High Power LEDs; Package: PSOP; No of Pins: 8; Qty per Container: 2500; Container: Reel
• Manufacturer: National Semiconductor

www.national.com
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: LM3402
The first example circuit will guide the user through compo-
nent selection for an architectural accent lighting application.
R
ON
and t
ON
FIGURE 11. VIN Pin with Additional Input Protection
FIGURE 12. Schematic for Design Example 1
20
A regulated DC voltage input of 24V ±10% will power a single
1W white LED at a forward current of 350 mA ±5%. The typical
forward voltage of a 1W InGaN LED is 3.5V, hence the esti-
mated average output voltage will be 3.7V. The objective of
this application is to place the complete current regulator and
LED in the compact space formerly occupied by an MR16
halogen light bulb. (The LED will be on a separate metal-core
PCB.) Switching frequency will be as fast as the 300 ns t
limit allows, with the emphasis on space savings over effi-
ciency. Efficiency cannot be ignored, however, as the con-
fined space with little air-flow requires a maximum tempera-
ture rise of 40°C in each circuit component. A complete bill of
materials can be found in Table 1 at the end of this datasheet.
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20192119
ON