Datasheet

V
OUT
- KV
IN
D =
V
OUT
V
OUT
x I
LED
K =
V
IN
x I
IN
'¶
K
V
OUT
V
IN
=
V
OUT
- V
IN
D =
V
OUT
1 - D
1
1
=
c
D
=
V
OUT
V
IN
¨
©
§
¸
¹
·
=
2'i
L
DT
S
'i
L
=
¨
¨
©
§
L
V
IN
¸
¸
¹
·
¨
¨
©
§
2L
V
IN
¸
¸
¹
·
x DT
S
t
L
i
L
i'
S
T
S
DT
( )
tL
I
L
V
IN
L
VV
OUT
IN
-
LM3410, LM3410Q
www.ti.com SNVS541G –OCTOBER 2007–REVISED MAY 2013
Figure 17. Inductor Current
(3)
The Duty Cycle (D) for a Boost converter can be approximated by using the ratio of output voltage (V
OUT
) to input
voltage (V
IN
).
(4)
Therefore:
(5)
Power losses due to the diode (D1) forward voltage drop, the voltage drop across the internal NMOS switch, the
voltage drop across the inductor resistance (R
DCR
) and switching losses must be included to calculate a more
accurate duty cycle (See Calculating Efficiency and Junction Temperature for a detailed explanation). A more
accurate formula for calculating the conversion ratio is:
Where
• η equals the efficiency of the LM3410 application. (6)
Or:
(7)
Therefore:
(8)
Inductor ripple in a LED driver circuit can be greater than what would normally be allowed in a voltage regulator
Boost and Sepic design. A good design practice is to allow the inductor to produce 20% to 50% ripple of
maximum load. The increased ripple shouldn’t be a problem when illuminating LEDs.
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