PAM2803SWAF095 datasheet(6/8 Pages) PAM

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Inductor Selection

Capacitor Selection

Diode Selection

LED Current Setting

The PAM2803 can use small value inductors due

to its switching frequency of 1 MHz. The value of

inductor will focus in the range of 2.2uH to 4.7uH

for most PAM2803 applications. In typical high

current

white

L ED

applications,

i t

i s

recommended to use a 4.7uH inductor. The

inductor should have low DCR (DC resistance) to

minimize the I R power loss, and it requires a

current rating of 2A to handle the peak inductor

current without saturating.

An input capacitor is required to reduce the input

ripple and noise for proper operation of the

PAM2803. For good input decoupling, Low ESR

(equivalent series resistance) capacitors should

be used at the input. At least 2.2uF input

capacitor is recommended for most applications.

A minimum output capacitor value of 6.8uF is

recommended

under

normal

operating

conditions, while a 10uF-22uF capacitor may be

required for higher power LED current. A

reasonable value of the output capacitor

depends on the LED current. The ESR of the

output capacitor is the important parameter to

determine the output voltage ripple of the

converter, so low ESR capacitors should be used

at the output to reduce the output voltage ripple.

The small size of ceramic capacitors is an

excellent choice for PAM2803 applications. The

X5R and X7R types are preferred because they

maintain capacitance over wide voltage and

temperature ranges.

It's indispensable to use a Schottky diode rated

at 2A with the PAM2803. Using a Schottky diode

with a lower forward voltage drop is better to

improve the power LED efficiency, and its voltage

rating should be greater than the output voltage.

application,

the

O N

S emiconductor

MBRA210LT3G is recommended.

The LED current is set by the single external Rs

resistor connected to the FB pin as shown in the

typical application circuit on page 1. The typical

FB reference is internally regulated to 95mV. The

LED current is 95mV/Rs. It's recommended to

use a 1% or better precision resistor for the

better LED current accuracy. The formula and

table 1 for Rs selection are shown as follows:

Rs=95mV/I

Table 1. Rs Resistor Value Selection

LED

PCB Layout Guidelines

As for all switching power supplies, the layout

and components placement of the PAM2803 is

an important step in the design; especially at

high peak currents and high switching

frequencies.

The input capacitor and output capacitor should

be placed respectively as close as possible to

the input pin and output pin of the IC; the inductor

and schottky diode should be placed as close as

possible to the switch pin by using wide and short

traces for the main current path; the current

sense resistor should be placed as close as

possible between the ground pin and feedback

pin.

Application Information

08/2007

PAM2803

3W High Power White LED Driver

Standard Value(

Ω)ILED(mA)

0.18

528

0.15

633

0.12

792

0.10

950

Power Analog Microelectronics Inc

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