Diodes AP8801 - Manual (Page 6)

AP8801
500mA LED STEP-DOWN CONVERTER
AP8801
Document number: DS31765 Rev. 7 - 2
6 of 14
www.diodes.com
June 2012
© Diodes Incorporated
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) is defined as:
SET
THD
LED
R
V
I
=
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 = 0.3A
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.
100
100
100
150
150
220
220
220
150
470
470
470
68
68
47
47
Switching Frequency @I = 500mA
LED
12V - 1 LED
24V - 3 LEDs
48V - 6 LEDs
0 50 100 150 200 250 300 400 450 500 350
INDUCTOR VALUE (µH)
Figure. 15 Switching Frequency vs. Inductor Value
F
R
E
Q
U
EN
C
Y
(k
H
z)
600
500
100
0
400
300
200