AP8801_0912 Datasheet, PDF (5/11 Pages) Diodes Incorporated – 500mA LED Step-down Converter

AP8801
500mA LED Step-down Converter
Application Information
LED Current Control
The LED current is controlled by the resistor RSET in Figure 1 connected between V_IN and SET. The nominal
average output current in the LED(s) is defined as:
I_LED
= ^VTHD
R_SET
If the CTRL pin is driven by an external voltage (lower than 2.5V), the average LED current is:
I_LED
= ^VCTRL
V_REF
V_THD
R_SET
LED current Versus RSET and VCTRL
600
500
0.4
0.82
400
300
200
100
0
0
0.47
1
0.56
1.2
0.68
1.5
0.82
0.47
1
2
1.2
0.68
1.5
0.82
1
1.2
1.5
2
2
3
3
3
0.15 0.3 0.45 0.6 0.75 0.9 1.05 1.2 1.35 1.5 1.65 1.8 1.95 2.1 2.25 2.4 2.55 2.7 2.85 3
RSET value [Ohms]
Figure 3: LED Current setting Vs R_SET and V_CTRL
LED current @
VCTRL = 1.25V
LED current @
VCTRL = 2.5V
LED current @
VCTRL = 0.625V
AP8801 Rev. 4
DS31765
5 of 11
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DECEMBER 2009
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