Diodes AP3039 - Manual (Page 16)

BOOST CONTROLLER AP3039
Data Sheet
16
BCD Semiconductor Manufacturing Limited Jun. 2010 Rev. 1. 6
Typical Application (Continued)
Note 2: The output voltage is decided by R5, R6 and the internal 0.5V reference. The output voltage accuracy is
determined by the accuracy of R5 and R6, for which the precise resistors are preferred.
V
OUT
=
Note 3: In this application, the LED current is controlled by the feedback resistor R5. LEDs current accuracy is
determined by regulator
‘ s feedback threshold accuracy and is independent of the LEDs ‘ forward voltage variation.
So the precise resistors are the better choices. The resistance of R5 is in inverse proportion to the LED current
since the feedback reference is fixed at 0.5V. The relation of R5 and the LED current can be expressed as below:
R5=
Note 4: The summation of LED current is determined by R5 and internal 0.5V reference same as the illustration in
Figure 22.
More detailed application information please refer to application note.
( )
R6 R5 *
R6
0.5V
+
LED
I
0.5V