Diodes PAM2803 - Manual (Page 6)

PAM2803
Document number: DSxxxxx Rev. 1 - 1
6 of 9
www.diodes.com
July 2013
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PAM2803
A Product Line of
Diodes Incorporated
Application Information
Inductor Selection
The PAM2803 can use small value inductors due to its switching frequency of 1MHz. The value of inductor will focus in the range of 2.2µH to
4.7µH for most PAM2803 applications. In typical high current white LED applications, it is recommended to use a 4.7µH inductor. The inductor
should have low DCR (DC resistance) to minimize the I 2 R power loss, and it requires a current rating of 2A to handle the peak inductor current
without saturating.
Capacitor Selection
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 2.2µF input capacitor is recommended for most applications.
A minimum output capacitor value of 6.8µF is recommended under normal operating conditions, while a 10µF-22µF capacitor may be required
for higher power LED current. A reasonable value of the output capaci tor 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.
Diode Selection
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. In application, the ON Semi conductor
MBRA210LT3G is recommended.
LED Current Setting
The LED current is set by the single external R
S
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/R
S
. It's recommended to use a 1% or better precision resistor for the
better LED current accuracy. The formula and table 1 for R
S
selection are shown as follows:
I / mV 95 R
LED S

Table 1. R
S
Resistor Value Selection
Standard Value ( Ω) I LED (mA)
0.18 528
0.15 633
0.12 792
0.10 950
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.