AP5724

Document number: DS31843 Rev. 4 - 2

8 of 15

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December 2013

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AP5724

Applications Information

Inductor Selection

A 10

μH to 22μH inductor is recommended for most AP5724 applications. For high efficiency the inductor should have low core losses at 1.2MHz

and low DCR (copper wire resistance). The inductor saturation current rating should also exceed the peak input current, especially for high load

current applications (like 3S8P).

Capacitor Selection

The small size of the ceramic capacitors are ideal for AP5724 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 1

μF input capacitor and a 1μF output capacitor

are sufficient for most AP5724 applications. For high output current applications like 3S8P, larger output capacitor of 2.2µF to 4.7µF is

recommended to minimize output ripple.

Diode Selection

Schottky diodes, with their low forward voltage drop and fast reverse recovery, are the ideal choices for AP5724 applications. The forward voltage

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 AP5724. Schottky diodes with higher current ratings usually have lower forward voltage drop and larger diode capacitance. Larger Schottky

diode capacitance can cause significant switching losses at the 1.2MHz switching frequency of the AP5724. A Schottky diode rated at 100mA to

200mA is sufficient for most AP5724 applications.

LED Current Control

Ω)

5

20

10

10

15

6.6

20

5

30

3.3

40

2.5

Open-Circuit Protection

In the cases of output open circuit, when the LEDs are disconnected from the circuit or the LEDs fail, the feedback voltage will be zero. The AP5724

will then switch at a high duty cycle resulting in a high output voltage, which may cause the SW and OVP pin voltage to exceed the voltage rating of

these pins. The OVP pin monitors the output voltage. If the output voltage reaches the over voltage protection threshold at the OVP pin (Figure 2),

the over voltage protection is activated and SW pin stops switching.

V

IN

SW

EN

GND

FB

AP5724

C

OUT

1uF

5

L1

22uH

D1

V

IN

1uF

OVP

x

x

Figure 2 LED Driver with Open-Circuit Protection