SC192
POWER MANAGEMENT
Applications Information
Selecting Components
When selecting components for the an SC192 application the main factors are typically performance, size and cost.
For higher performance the designer will select higher values of input and output capacitors to reduce ripple
current and voltage. However, for an application that can tolerate higher ripple, less expensive and smaller compo-
nents can be utilized. The schematics below show two possibilities. The first shows the use of 10μF capacitors on
the input and output with L1 = 10μH, while the second shows the use of smaller less expensive 4.7μF capacitors
and L1 = 4.7μH. The only circuit consideration for choosing one over the other is the compensation components C4
& R8. When these components are in place the values of R2 can be chosen for a given output voltage. The values
that should be used are indicated in Table 1 below. Using a different value for R1 is not advised since this will
change the loop characteristics and may cause the supply to become unstable. Any output voltage is achievable
using R1 of 442k and then selecting R2 to achieve the desired output voltage. The equation for VOUT is:
⎛
R1
⎞
Vout
= ⎜
+
1
⎟ •
0.75
⎝
R2
⎠
Because the SC192 has external compensation the use of small inexpensive ceramic capacitors can be used for
the output capacitor allowing the designer greater flexibility.
VIN
1
2
3
4
5
C1
10uF
C3
0.1uF
C4
470pF
R8
12k
VIN
BP
GND
PGND
LX
EN
10
L1
9
10uH
8
7
6
C6
10uF
R2
C5
47pF
R1
442k
VOUT
COMP SY NC
ADJ
ILIM
SC192
VIN
1
2
3
4
5
C1
4.7uF
C3
0.1uF
C4
470pF
R8
6.19k
VIN
BP
GND
PGND
LX
EN
10
L1
9
4.7uH
8
7
6
C6
4.7uF
R2
C5
47pF
R1
442k
VOUT
COMP SY NC
ADJ
ILIM
SC192
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2007 Semtech Corp.
9
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