MP1583 查看數據表（PDF） - Unspecified
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MP1583 Datasheet PDF : 11 Pages
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Monolithic Power Systems
Inductor
The inductor is required to supply constant
current to the output load while being driven by
the switched input voltage. A larger value
inductor results in less ripple current that in
turn results in lower output ripple voltage.
However, the larger value inductor has a larger
physical size, higher series resistance, and/or
lower saturation current. Choose an inductor
that does not saturate under the worst-case
load conditions. A good rule for determining
the inductance is to allow the peak-to-peak
ripple current in the inductor to be
approximately 30% of the maximum load
current. Also, make sure that the peak
inductor current (the load current plus half the
peak-to-peak inductor ripple current) is below
the TBDA minimum current limit. The
inductance value can be calculated by the
equation:
L = (VOUT) * (VIN-VOUT) / VIN * f * ∆I
Where VOUT is the output voltage, VIN is the
input voltage, f is the switching frequency, and
∆I is the peak-to-peak inductor ripple current.
Table 2 lists a number of suitable inductors
from various manufacturers.
Table 2: Inductor Selection Guide
Vendor/
Model
Core
Type
Core
Material
Sumida
CR75
CDH74
CDRH5D28
CDRH5D28
CDRH6D28
CDRH104R
Toko
D53LC
Type A
D75C
D104C
D10FL
Coilcraft
DO3308
DO3316
Open
Open
Shielded
Shielded
Shielded
Shielded
Shielded
Shielded
Shielded
Open
Open
Open
Ferrite
Ferrite
Ferrite
Ferrite
Ferrite
Ferrite
Ferrite
Ferrite
Ferrite
Ferrite
Ferrite
Ferrite
Package
Dimensions (mm)
WL
H
7.0 7.8 5.5
7.3 8.0 5.2
5.5 5.7 5.5
5.5 5.7 5.5
6.7 6.7 3.0
10.1 10.0 3.0
5.0 5.0 3.0
7.6 7.6 5.1
10.0 10.0 4.3
9.7 11.5 4.0
9.4 13.0 3.0
9.4 13.0 5.1
MP1583
3A, 23V
Step Down Converter
Input Capacitor
The input current to the step-down converter is
discontinuous, and so a capacitor is required
to supply the AC current to the step-down
converter while maintaining the DC input
voltage. A low ESR capacitor is required to
keep the noise at the IC to a minimum.
Ceramic capacitors are preferred, but tantalum
or low-ESR electrolytic capacitors may also
suffice.
The input capacitor value should be greater
than 10µF. The capacitor can be electrolytic,
tantalum or ceramic. However since it absorbs
the input switching current it requires an
adequate ripple current rating. Its RMS current
rating should be greater than approximately
1/2 of the DC load current.
For insuring stable operation C2 should be
placed as close to the IC as possible.
Alternately a smaller high quality ceramic
0.1µF capacitor may be placed closer to the IC
and a larger capacitor placed further away. If
using this technique, it is recommended that
the larger capacitor be a tantalum or
electrolytic type. All ceramic capacitors should
be places close to the MP1583.
Output Capacitor
The output capacitor is required to maintain
the DC output voltage. Low ESR capacitors
are preferred to keep the output voltage ripple
low. The characteristics of the output
capacitor also affect the stability of the
regulation control system. Ceramic, tantalum,
or low ESR electrolytic capacitors are
recommended. In the case of ceramic
capacitors, the impedance at the switching
frequency is dominated by the capacitance,
and so the output voltage ripple is mostly
independent of the ESR. The output voltage
ripple is estimated to be:
VRIPPLE ~= 1.4 * VIN * (fLC/fSW)^2
MP1583 Rev 2.0_06/30/04
www.monolithicpower.com
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