®
ACT2103
Rev 2, 23-May-12
output load. This inductor current has a ripple that is
dependent on the inductance value:
Higher inductance reduces the peak-to-peak ripple
current. The trade off for high inductance value is
the increase in inductor core size and series
resistance, and the reduction in current handling
capability. In general, select an inductance value L
based on ripple current requirement:
APPLICATIONS INFORMATION
Output Voltage Setting
Figure 1:
Output Voltage Setting
V
OUT
×
(
V
IN
_
V
OUT
)
L
=
V
IN
f
SW
I
LOADMAX
K
RIPPLE
Figure 1 shows the connections for setting
output voltage. Select the proper ratio of the
feedback resistors R
FB1
and R
FB2
based on
output voltage. Typically, use R
FB2
≈
10kΩ
determine R
FB1
from the following equation:
the
two
the
and
(2)
⎞
⎛
V
OUT
R
FB
1
=
R
FB
2
⎜
−
1
⎟
⎠
⎝
0 . 923
V
Table 1:
Recommended Resistance Values
V
OUT
R1
R2
where V
IN
is the input voltage, V
OUT
is the output
voltage, f
SW
is the switching frequency, I
LOADMAX
is
the maximum load current, and K
RIPPLE
is the ripple
factor. Typically, choose K
RIPPLE
= 20~40% to
correspond to the peak-to-peak inductor ripple
current being 20~40%
of the maximum load
current.
With a selected inductor value the peak-to-peak
inductor current is estimated as:
(1)
I
LPK
−
PK
=
V
OUT
×
(
V
IN
−
V
OUT
)
L
×
V
IN
×
f
SW
(3)
The peak inductor current is estimated as:
5.0V
3.3V
2.5V
1.8V
1.2V
1.0V
47kΩ
27.4kΩ
18kΩ
10.2kΩ
3.3kΩ
1kΩ
10.5kΩ
10.5kΩ
10.5kΩ
10.5kΩ
10.5kΩ
10.5kΩ
I
LPK
=
I
LOADMAX
+
1
I
LPK
−
PK
2
(4)
The selected inductor should not saturate at I
LPK.
The maximum output current is calculated as:
I
OUTMAX
=
I
LIM
_
1
I
_
2
LPK PK
(5)
Inductor Selection
The inductor maintains a continuous current to the
Table 2:
Inductor Values Range and Typical Compensation
V
OUT
5.0V
L
LIM
is the internal current limit, which is typically
4.5A, as shown in Electrical Characteristics Table.
V
IN
7V ~ 1 8V
L
10µH ~ 22µH
C
OUT
330µF/10V
22µF/ Ceramic × 2
330µF/10V
22µF/ Ceramic × 2
470µF/10V
22µF/ Ceramic × 2
470µF/10V
22µF/ Ceramic × 2
470µF/10V
22µF/ Ceramic × 2
-7-
R
COMP
25kΩ
10kΩ
21kΩ
8.2kΩ
12kΩ
8.2kΩ
12kΩ
8.2kΩ
10kΩ
8.2kΩ
C
COMP
2.2nF
2.2nF
2.2nF
2.2nF
4.7nF
4.7nF
10nF
10nF
10nF
10nF
C
COMP2
220PF
N/A
220PF
N/A
220PF
N/A
220PF
N/A
220PF
N/A
www.active-semi.com
3.3V
5V ~ 18V
8.2µH ~ 15µH
1.8V
4.5V ~ 18V
3.3µH ~ 10µH
1.2V
4.5V ~ 12V
2.5µH ~ 9.1µH
1.0V
4.5V ~ 10V
2.2µH ~ 8.2µH
Innovative Power
TM
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ACTIVE-SEMI [ ACTIVE-SEMI, INC ]
