SS6638-27G 데이터 시트보기 (PDF) - Silicon Standard Corp.
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SS6638-27G Datasheet PDF : 19 Pages
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SS6638G
EL
=
1
2
L
×
IPK
2
Power required from the inductor per cycle must
be equal or greater than
PL/FSW = (VOUT + VD − VIN)(IOUT)( 1 )
FSW
in order for the converter to regulate the output.
When loading is over IOB, PFM converter
operates in continuous mode. Inductor peak
current can be derived from
IPK = VOUT + VD − VSW − x IOUT +
VIN − VSW
2
VIN − VSW TON 1 − x
2L 2
Valley current (Iv) is
Iv = VOUT + VD − VSW − x IOUT − VIN − VSW ×
VIN − VSW
2
2L
TON 1 − x
2
Table 1 Indicates resistance and height for each coil.
Power Inductor Type
Inductance
( µH )
22
DS1608
47
Coilcraft SMT Type
100
(www.coilcraft.com)
22
DO3316
47
47
Sumida SMT Type CD54
100
47
Hold SMT Type PM54
100
Hold SMT Type PM75
33
Resistance
(Ω)
0.10
0.18
0.38
0.08
0.14
0.25
0.50
0.25
0.50
0.11
Rated Current
(A)
0.7
0.5
0.3
2.7
1.8
0.7
0.5
0.7
0.5
1.2
Height
(mm)
2.9
5.2
4.5
4.5
5.0
CAPACITOR SELECTION
A poor choice for an output capacitor can result in
poor efficiency and high output ripple. Ordinary
aluminum electrolytics, while inexpensive, may
have unacceptably poor ESR and ESL. There are
low ESR aluminum capacitors for switch mode
DC-DC converters which work much better than
general proposetypes. Tantalum capacitors
provide still better performance but are more
expensive. OS-CON capacitors have extremely
low ESR in a small size. If capacitance is
reduced, output ripple will increase.
Most of the input supply is provided by the input
bypass capacitor; the capacitor voltage rating
should be at least 1.25 times greater than the
maximum input voltage.
DIODE SELECTION
Speed, forward drop, and leakage current are the
three main considerations in selecting a rectifier
diode. Best performance is obtained with
a Schottky rectifier diode, such as the 1N5818,
or the SS13 and B0530W in surface mount packages.
For lower output power a 1N4148 can be used
although efficiency and start-up voltage will suffer
substantially.
8/21/2005 Rev.2.3
www.SiliconStandard.com
17 of 19
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