AP5725

WHITE LED STEP-UP CONVERTER

AP5725

Document number: DS31844 Rev. 3 - 2

10 of 17

www.diodes.com

July 2010

© Diodes Incorporated

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 AP5725 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

AP5725

C

OUT

1uF

12

L1

22uH

D1

V

IN

1uF

OVP

x

x

Figure 2. LED Driver with Open-Circuit Protection

Dimming Control

There are four different types of dimming control circuits:

1. Using a PWM Signal to EN Pin

With the PWM signal applied to the EN pin, the AP5725 is turned on or off by the PWM signal. The LEDs operate

at either zero or full current. The average LED current increases proportionally with the duty cycle of the PWM

signal. A 0% duty cycle will turn off the AP5725 and corresponds to zero LED current.

A 100% duty cycle

corresponds to full current. The typical frequency range of the PWM signal is below 2kHz.