AP5726 Datasheet, PDF (10/16 Pages) Diodes Incorporated – WHITE LED STEP-UP CONVERTER

AP5726
WHITE LED STEP-UP CONVERTER
Application 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 AP5726 will then switch at a high duty cycle resulting in a high output
voltage, which may cause the SW pin voltage to exceed the level of the over voltage protect function. The
OVP pin can detect the output voltage and monitor if the output voltage reach to the protect voltage level
(Figure 2). Once OVP is activated, SW pin stops switching.
V_IN
C_IN
1uF
L1
22uH
D1
V_IN
SW
AP5726 ^OVP
EN
FB
GND
C_OUT
1uF
x
x
RSET
15
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 AP5726 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 AP5726 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.
AP5726 Rev. 1
10 of 16
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JUNE 2009
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