
AP8802
1A LED STEP-DOWN CONVERTER
Application Information
LED Current Control
The LED current is controlled by the resistor R SET in Figure 14 connected between V IN and SET. The nominal average output current in the
LED(s) with the CTRL pin open circuit is defined as:
I LED =
V THD
R SET
where V THD is the voltage between the V IN and SET pins and is nominally 200mV.
Figure. 14 Typical Application Circuit for I LED = 1A
Inductor Selection
This section highlights how to select the inductor suitable for the application requirements in terms of switching frequency, LED current
accuracy and temperature.
500
450
400
68
Switching Frequency @ I LED = 700mA
12V - 3 LEDs
24V - 5 LEDs
350
47
100
48V - 10 LEDs
300
250
200
68
100
150
220
150
150
100
47
68
220
470
50
100
150
220
470
0
470
0
50
100
150
200
250
300
350
400
450
500
INDUCTOR VALUE (μH)
Figure. 15 Switching Frequency vs. Inductor Value
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.
AP8802
Document number: DS31766 Rev. 9 - 2
7 of 19
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May 2012
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