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2
1
3
4
7
8
6
5
C1
V
IN
V
OUT
SW
BOOT
GND
DIM
VIN
VCC
RON
CS
C3
Q1
L1
R3
LEDs on separate PCB
Optional
C4
U1
D1
C2
C5
LM3404
R2
R1
Improved Average
Current Circuit
www.ti.com Modified Application Circuit Design Example 3
Figure 9. Improved Average LED Current Application Circuit
Table 7. Example 3 On and Off Times
Three Series LEDs
V
IN
(V) V
OUT
(V) R
ON
t
ON
t
OFF
36 10.4 113 kΩ 5.92E-07 1.09E-07
48 10.4 113 kΩ 4.03E-07 1.12E-06
60 10.4 113 kΩ 3.06E-07 1.14E-06
Four Series LEDs
36 13.8 113 kΩ 6.83E-07 7.78E-07
48 13.8 113 kΩ 4.43E-07 8.21E-07
60 13.8 113 kΩ 3.28E-07 8.41E-07
Five Series LEDs
36 17.2 113 kΩ 8.06E-07 5.77E-07
48 17.2 113 kΩ 4.92E-07 6.34E-07
60 17.2 113 kΩ 3.54E-07 6.59E-07
13
SNVA342E–July 2008–Revised April 2013 AN-1839 LM3402/LM3404 Fast Dimming and True Constant LED Current
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