PAM2805

Document number: DSxxxxx Rev. 1 - 0

6 of 9

www.diodes.com

July 2013

© Diodes Incorporated

PAM2805

A Product Line of

Diodes Incorporated

Application Information

Inductor Selection

The PAM2805 can use small value inductors due to its switching frequency of 1 MHz. The value of inductor will focus in the range of 2.2µH to

4.7µH for most PAM2805 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

without saturating.

Capacitor Selection

An input capacitor is required to reduce the input ripple and noise for proper operation of the PAM2805. 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 PAM2805 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 PAM2805. 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. SS22 is recommended Schottky diode for

rectifier.

LED Current Setting

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/R1. It's recommended to use a 1% or better precision resistor for the

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3 Modes Cycling

The PAM2805 has three modes: 100% brightness, 25% brightness and blinking (typical 8.5Hz).

The mode change is triggered by power on/off actions and cycles in the following sequence: bright, dimming, blinking and back to bright mode.

The PAM2805 will reset to the bright mode after being power off for more than 5 seconds.

Low Voltage Start-Up and Soft-Start

current is 200mA.

The soft-start function is made by clamping the output voltage of error amplifier with another voltage source which increases slowly from zero to

time of the inductor will be limited by the smaller duty so that the inrush current can be reduced to an acceptable value.

Over Voltage Protection

Over Current Protection

NMOS is turned off so that the inductor will be forced to leave charging stage and enter discharging stage. Therefore, the inductor peak current