AP8801_0912 Datasheet, PDF (7/11 Pages) Diodes Incorporated – 500mA LED Step-down Converter

AP8801
500mA LED Step-down Converter
Application Information (Continued)
The inductor influences the LED current accuracy that the system is able to provide. The following section
highlights how to select the inductor in relation to the device packages and the LED current, while maintaining
the chip temperature below 70˚C.
Figure 5: Minimum recommended inductor with 500mA LED current
Capacitor Selection
The small size of ceramic capacitors makes them ideal for AP8801 applications. X5R and X7R types are
recommended because they retain their capacitance over wider voltage and temperature ranges than other
types such as Z5U. A 2.2μF input capacitor is sufficient for most intended applications of AP8801.
A 4.7μF input capacitor is suggested for application with an input voltage equal or higher than 40V.
Diode Selection
Schottky diodes, e.g. B1100, with their low forward voltage drop and fast reverse recovery, are the ideal
choice for AP8801 applications.
PWM Dimming
A Pulse Width Modulated (PWM) signal with a max resolution of 8bit, can be applied to the CTRL pin to
change the output current to a value above or below the nominal average value set by resistor RSET. To
achieve this resolution the PWM frequency has to be lower than 500Hz.
AP8801 Rev. 4
DS31765
7 of 11
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DECEMBER 2009
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