SLVS859 – JUNE 2008
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Typically, it is recommended that the inductor current ripple is below 20% of the average inductor current. The
following equation can therefore be used to calculate the inductor value:
æ
V
S
-V
IN
ö æ h ö
æ
V
IN
ö
L=
ç
×
ç
÷
×
ç
÷
÷
è
V
S
ø
è
Iout_max×f
ø è
0.35
ø
2
(1)
Table 1. Inductor Selection
L
(µH)
3.3
4.7
3.3
3.3
4.7
5
6.8
10
6.8
10
10
6.8
SUPPLIER
COMPONENT
CODE
1.2 MHz
Sumida
Sumida
Sumida
Sumida
Würth Elektronik
Coilcraft
Sumida
Coilcraft
Sumida
Sumida
Würth Elektronik
Sumida
CDH38D09
CDPH36D13
CDPH4D19F
CDRH6D12
7447785004
MSS7341
650 kHz
CDP14D19
LPS4414
CDRH6D12/LD
CDR6D23
744778910
CDRH6D26HP
5.2 x 5.2 x 2
4.3 × 4.3 × 1.4
6.7 x 6.7 x 1.5
5 × 5 × 2.4
7.3 × 7.3 × 3.2
7 x 7 x 2.8
50
380
95
133
51
52
1
1.2
1.25
1.75
2.2
2.9
4x4x1
5 × 5 × 1.5
5.2 x 5.2 x 2
6.7 x 6.7 x 1.5
5.9 × 6.2 × 3.3
7.3 × 7.3 × 4.1
240
155
33
62
60
24
1.25
1.36
1.5
2.2
2.5
2.9
SIZE
(L×W×H mm)
DCR TYP
(mΩ)
Isat (A)
Rectifier Diode Selection
To achieve high efficiency, a Schottky type should be used for the rectifier diode. The reverse voltage rating
should be higher than the maximum output voltage of the converter. The averaged rectified forward current I
avg
,
the Schottky diode needs to be rated for, is equal to the output current I
out
:
I
avg
=
I
out
Usually a Schottky diode with 2 A maximum average rectified forward current rating is sufficient for most
applications. The Schottky rectifier can be selected with lower forward current capability depending on the output
current I
out
but has to be able to dissipate the power. The dissipated power is the average rectified forward
current times the diode forward voltage.
P
D
= I
avg
× V
forward
Typically the diode should be able to dissipate around 500mW depending on the load current and forward
voltage.
Table 2. Rectifier Diode Selection
CURRENT
RATING Iavg
750 mA
1A
1A
1A
1A
Vr
20 V
20 V
20 V
20 V
20 V
V
forward / Iavg
0.425 V /
750 mA
0.39 V / 1 A
0.52 V / 1 A
0.5 V / 1 A
0.44 V / 1 A
SUPPLIER
Fairchild Semiconductor
NXP
Vishay Semiconductor
Vishay Semiconductor
Vishay Semiconductor
COMPONENT
CODE
FYV0704S
PMEG2010AEH
B120
SS12
MSS1P2L
PACKAGE
TYPE
SOT 23
SOD 123
SMA
SMA
µ-SMP
(Low
Profile)
10
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