Datasheet
Vin
Vo
Iin
Io
K
2.7V
3.1V
770 mA
500 mA
75%
Vin
Vo
Iin
Io
K
3.3V
3.1V
600 mA
500 mA
80%
Vin
Vo
Iin
Io
K
5V
3.1V
375 mA
500 mA
83%
V
O
=
D
¸
¹
·
¨
©
§
(V
IN
x K)+
V
O
V
O
V
IN
=
1 - D
D
x K
¸
¹
·
¨
©
§
1
+ +
¸
¹
·
¨
©
§
R
R
L1
¸
¸
¹
·
¨
¨
©
§
D
2
D
2
'
¨
©
§
R
R
ON
¸
¹
·
¸
¸
¹
·
¨
¨
©
§
D
D
2
'
1+
+
¸
¸
¹
·
R
R
L2
V
D
V
O
¨
¨
©
§
¨
¨
¨
¨
¨
¨
©
§
¸
¸
¸
¸
¸
¸
¹
·
K=
1
+ +
¸
¹
·
¨
©
§
R
R
L1
¸
¸
¹
·
¨
¨
©
§
D
2
D
2
'
¨
©
§
R
R
ON
¸
¹
·
¸
¸
¹
·
¨
¨
©
§
D
D
2
'
1+
+
¸
¸
¹
·
R
R
L2
V
D
V
O
¨
¨
©
§
¸
¸
¹
·
¨
¨
©
§
D
=
V
o
V
IN
D
'
¨
¨
¨
¨
¨
¨
©
§
¸
¸
¸
¸
¸
¸
¹
·
x
=
I
L1
and
D
¸
¹
·
¨
©
§
'
D
R
¸
¹
·
V
O
¨
©
§
=
L2
I
R
¸
¹
·
V
O
¨
©
§
LM2735
www.ti.com
SNVS485F –JUNE 2007–REVISED APRIL 2013
Using inductor volt-second balance & capacitor charge balance, the following equations are derived:
(56)
(57)
Therefore:
(58)
One can see that all variables are known except for the duty cycle (D). A quadratic equation is needed to solve
for D. A less accurate method of determining the duty cycle is to assume efficiency, and calculate the duty cycle.
(59)
(60)
Figure 34. Efficiencies for Typical SEPIC Application
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