Datasheet

LM2524D, LM3524D
www.ti.com SNVS766E –JUNE 2009–REVISED MAY 2013
Figure 28. Basic Step-Up Switching Regulator
Figure 29. Relation of Switch Timing to Inductor Current in Step-Up Regulator
(16)
Since ΔI
L
+ = ΔI
L
−, V
IN
t
ON
= V
o
t
OFF
− V
IN
t
OFF
,
and neglecting V
SAT
and V
D1
(17)
The above equation shows the relationship between V
IN
, V
o
and duty cycle.
In calculating input current I
IN(DC)
, which equals the inductor's DC current, assume first 100% efficiency:
(18)
for η = 100%, P
OUT
= P
IN
(19)
This equation shows that the input, or inductor, current is larger than the output current by the factor (1 +
t
ON
/t
OFF
). Since this factor is the same as the relation between V
o
and V
IN
, I
IN(DC)
can also be expressed as:
(20)
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