SS6642-27G 查看數據表（PDF） - Silicon Standard Corp.
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SS6642-27G Datasheet PDF : 22 Pages
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EL = 1 L × Ipk 2
2
The power supplied by the inductor per
cycle must be equal to or greater than
PL/fSW = (VOUT + VD − VIN) * (IOUT) * ( 1 )
fsw
in order for the converter to regulate the output.
SS6642G
When loading is over IOB, the PFM controller
operates in continuous mode. Inductor peak
current can be derived from
IPK = VOUT+VD−VSW− x*IOUT+ VIN−VSW*TON *1− x
VIN−VSW 2
2L
2
Valley current (Iv) is
IV = VOUT+ VD−VSW− x*IOUT− VIN−VSW* TON*1− x
VIN−VSW 2
2L
2
Table 1 Indicates resistance and height for each coil.
Power Inductor Type
Inductance
( µH )
22
Coilcraft SMT Type DS1608
47
(www.coilcraft.com)
100
22
DO3316
47
47
Sumida SMT Type CD54
100
47
Hold SMT Type PM54
100
Hold SMT Type PM75
33
Rated Current
Resistance ( Ω )
(A)
0.10
0.7
0.18
0.5
0.38
0.3
0.08
2.7
0.14
1.8
0.25
0.7
0.50
0.5
0.25
0.7
0.50
0.5
0.11
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 types. Tantalum capacitors provide
still better performance but are more expensive.
OSCON capacitors have extremely low ESR and
small size. If capacitance is reduced, output rip-
ple will increase.
Most of the input supply is applied to the input
bypass capacitor, so 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 Schottky
rectifier diodes such as the 1N5819. SSC also has
Schottkies for surface-mount. For lower output
power a 1N4148 can be used, although efficiency
and start-up voltage will suffer substantially.
1/15/2005 Rev.2.10
www.SiliconStandard.com
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