AP5725_10 Datasheet, PDF (10/17 Pages) Diodes Incorporated – WHITE LED STEP-UP CONVERTER

AP5725
WHITE LED STEP-UP CONVERTER
Applications Information (Continued)
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
C _IN
1uF
L1
22uH
D1
V_IN
SW
AP5725 ^OVP
EN
FB
GND
C_OUT
1uF
x
x
RSET
12
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.
AP5725
Document number: DS31844 Rev. 3 - 2
10 of 17
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July 2010
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