®
ACT2102
Rev 2, 23-May-12
APPLICATIONS INFORMATION
dependent on the inductance value:
Output Voltage Setting
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:
Figure 1:
Output Voltage Setting
_
VOUT × V VOUT
IN
(2)
L =
VINfSWILOADMAXKRIPPLE
where VIN is the input voltage, VOUT is the output
voltage, fSW is the switching frequency, ILOADMAX is
the maximum load current, and KRIPPLE is the ripple
factor. Typically, choose KRIPPLE = 20~40% to
correspond to the peak-to-peak inductor ripple
Figure 1 shows the connections for setting the
output voltage. Select the proper ratio of the two
feedback resistors RFB1 and RFB2 based on the
output voltage. Typically, use RFB2 ≈ 10kꢀ and
determine RFB1 from the following equation:
current being 20~40%
current.
of the maximum load
V OUT
⎛
⎜
⎞
⎟
With a selected inductor value the peak-to-peak
inductor current is estimated as:
(1)
R
= R
FB 2
− 1
FB
1
0 .923 V
⎝
⎠
_
Table 1:
Recommended Resistance Values
VOUT × VIN VOUT
ILPK _
=
(3)
(4)
PK
L×VIN ×fSW
The peak inductor current is estimated as:
VOUT
5.0V
3.3V
2.5V
1.8V
1.2V
1.0V
R1
R2
1
47kꢀ
27.4kꢀ
18kꢀ
10.2kꢀ
3.3kꢀ
1kꢀ
10.5kꢀ
10.5kꢀ
10.5kꢀ
10.5kꢀ
10.5kꢀ
10.5kꢀ
ILPK =ILOADMAX
+
ILPK_
PK
2
The selected inductor should not saturate at ILPK.
The maximum output current is calculated as:
1
_
IOUTMAX = ILIM
ILPK _
PK
(5)
2
LLIM is the internal current limit, which is typically
3.5A, as shown in Electrical Characteristics Table.
Inductor Selection
The inductor maintains a continuous current to the
output load. This inductor current has a ripple that is
Table 2:
Inductor Values Range and Typical Compensation
VOUT
VIN
L
COUT
RCOMP
25kꢀ
10kꢀ
21kꢀ
8.2kꢀ
12kꢀ
8.2kꢀ
12kꢀ
8.2kꢀ
10kꢀ
8.2kꢀ
CCOMP
2.2nF
2.2nF
2.2nF
2.2nF
4.7nF
4.7nF
10nF
10nF
10nF
10nF
CCOMP2
220PF
N/A
330µF/10V
5.0V
7V ~ 18V
10µH ~ 33µH
22µF/ Ceramic × 2
330µF/10V
220PF
N/A
3.3V
1.8V
1.2V
1.0V
5V ~ 18V
4.5V ~ 18V
4.5V ~ 16V
4.5V ~ 13V
8.2µH ~ 22µH
5.6µH ~ 15µH
4µH ~ 12µH
22µF/ Ceramic × 2
470µF/10V
220PF
N/A
22µF/ Ceramic × 2
470µF/10V
220PF
N/A
22µF/ Ceramic × 2
470µF/10V
220PF
N/A
3.3µH ~ 10µH
22µF/ Ceramic × 2
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