AP5725 datasheet(9/16 Pages) DIODES

9 / 16 page

AP5725

WHITE LED STEP-UP CONVERTER

AP5725 Rev. 1

9 of 16

JUNE 2009

www.diodes.com

Inductor Selection

A 10μH~22μH inductor is recommended for most AP5725 applications. Although small size and high

efficiency are major concerns, the inductor should have low core losses at 1.2MHz and low DCR (copper wire

resistance).

Capacitor Selection

The small size of ceramic capacitors are ideal for AP5725 applications. X5R and X7R types are

recommended because they retain their capacitance over wider voltage and temperature ranges than other

types such as Y5V or Z5U. A 1μF input capacitor and a 1μF output capacitor are sufficient for most AP5725

applications.

Diode Selection

Schottky diodes, with their low forward voltage drop and fast reverse recovery, are the ideal choices for

AP5725 applications. The forward voltage drop of a Schottky diode represents the conduction losses in the

diode, while the diode capacitance (CT or CD) represents the switching losses.

For diode selection, both

forward voltage drop and diode capacitance need to be considered.

Schottky diodes with higher current

ratings usually have lower forward voltage drop and larger diode capacitance, which can cause significant

switching losses at the 1.2MHz switching frequency of the AP5725. A Schottky diode rated at 100mA to

200mA is sufficient for most AP5725 applications.

LED Current Control

The LED current is controlled by the feedback resistor (RSET in Figure 1). The feedback reference is 0.25V.

The LED current is 0.25V/ RSET. In order to have accurate LED current, precision resistors are preferred (1% is

recommended). The formula and table for RSET selection are shown below.

RSET = 0.25V/ILED (See Table 1)

Table 1. RSET Resistor Value Selection

ILED (mA)

RSET (Ω)

16.6

12.5

8.3

Application Information

AP5725 Datasheet(PDF) 9 Page - Diodes Incorporated