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LT3474/LT3474-1

3474fd

APPLICATIONS INFORMATION

LED Voltage Range

The LT3474 can drive LED voltages from 2.4V to 12V. The

LT3474-1 can drive LED voltages from 2.4V to 30V. Be

careful not to exceed the ABSMAX rating of the OUT, LED,

or BOOST pins of the LT3474-1 since the internal output

clamp is disabled. See the Typical Application section for

an example of adding an external output clamp. If the

LED voltage can drift below 2.4V due to temperature or

component variation, add extra series resistance to bring

the overall voltage above 2.4V.

Layout Hints

As with all switching regulators, careful attention must

be paid to the PCB layout and component placement. To

maximize efﬁciency, switch rise and fall times are made

VIN

GND

SHDN

PWM

VIA TO LOCAL GND PLANE

VIA TO OUT

Figure 8. Recommended Component Placement

as short as possible. To prevent electromagnetic interfer-

ence (EMI) problems, proper layout of the high frequency

switching path is essential. The voltage signal of the SW

and BOOST pins have sharp rise and fall edges. Minimize

the area of all traces connected to the BOOST and SW

pins and always use a ground plane under the switching

regulator to minimize interplane coupling. In addition, the

ground connection for frequency setting resistor RT (refer

to Figure 1) should be tied directly to the GND pin and

not shared with any other component, ensuring a clean,

noise-free connection.

B130 Datasheet(PDF) 17 Page - Linear Technology