AP8800 Datasheet, PDF (6/11 Pages) Diodes Incorporated – 350mA LED Step-Down Converter

Application Information (Continued)
AP8800
350mA LED Step-Down Converter
Switching Frequency
700
600
500
400
300
200
100
0
0
100
47
150
68
220
100
150
220
470
470
50
100
150
200
250
300
350
400
450
500
Inductor Value [uH]
12V - 1LED
24V - 3 LEDs
28V - 4LEDs
Figure 3: Switching Frequency Vs Supply voltage, Inductor, and number of LEDs
Capacitor Selection
The small size of ceramic capacitors makes them ideal for AP8800 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 1μF input capacitor is sufficient for most intended applications of AP8800.
Diode Selection
Schottky diode, e.g. B140, with their low forward voltage drop and fast reverse recovery, is the ideal choice for
AP8800 applications.
PWM Dimming
A Pulse Width Modulated (PWM) signal with a max resolution of 8bit can be applied to the CTRL pin to
regulate the output current to a value above or below the nominal average value set by resistor RSET.
Miscellaneous
To ensure optimal performance, RSVD pin should be connected to the GND pin with the shortest trace length.
AP8800 Rev. 1
6 of 11
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MARCH 2009
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