User manual

V
OUT
V
IN
x K
t
OFF
= t
ON
- 1
D =
V
OUT
V
IN
x K
=
t
ON
t
ON
+ t
OFF
t
ON
= k x
R
ON
V
IN
www.ti.com Application Circuit Calculations
Figure 6. V
OUT-MAX
vs f
SW
Figure 7. V
OUT-MIN
vs f
SW
(13)
R
ON
= 135 kΩ (use standard value of 137 kΩ)
t
ON
= 306 ns
Check to see if t
OFF
minimum is satisfied. This occurs when V
IN
is at its minimum value.
At V
IN
= 36V, and R
ON
= 137 kΩ calculate t
ON
from previous equation.
t
ON
= 510 ns
We know that:
(14)
Rearranging the above equation and solving for t
OFF
with t
ON
set to 510 ns
(15)
t
OFF
= 938 ns (satisfied)
7
SNVA342E–July 2008–Revised April 2013 AN-1839 LM3402/LM3404 Fast Dimming and True Constant LED Current
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