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參數(shù)資料
| 型號： | SC2441A |
| 廠商： | Semtech Corporation |
| 英文描述： | 1.8V to 20V Input 2-Phase Synchronous Step-down Controllers with Step-up Converter |
| 中文描述： | 1.8V至20V的輸入2相同步降壓與升壓轉(zhuǎn)換器控制器 |
| 文件頁數(shù)： | 28/37頁 |
| 文件大?。?/td> | 1024K |
| 代理商： | SC2441A |
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28
2006 Semtech Corp.
www.semtech.com
POWER MANAGEMENT
Applications Information
SC2441A
2
b
1
a
1
2
b
1
2
a
1
2
2
b
1
a
1
2
a
1
a
1
2
b
1
b
1
2
b
1
2
a
1
2
b
1
a
1
b
1
a
1
eq
)
C
C
(
C
C
)
R
R
(
)
C
R
C
R
(
C
C
)
R
R
(
R
R
:
(
R
where R
1a
and C
1a
are the ESR and capacitance of
electrolytic capacitors, and R
1b
and C
1b
are the ESR and
capacitance of the ceramic capacitors respectively
(Figure 17).
C1a
R1a
C1b
R1b
Ceq
Req
Figure 17. Equivalent RC branch.
R
eq
and C
eq
are both functions of frequency. For rigorous
design, the equivalent ESR should be evaluated at the
ripple frequency for voltage ripple calculation when both
ceramic and electrolytic capacitors are used. If R
1a
= R
1b
= R
1
and C
1a
= C
1b
= C
1
, then R
eq
and C
eq
will be frequency-
independent and
R
eq
= 1/2 R
1
and C
eq
= 2C
1
.
Input Capacitor (C
in
) in Step-down Sections
The input supply to the converter usually comes from a
pre-regulator. Since the input supply is not ideal, input
capacitors are needed to filter the current pulses at the
switching frequency. A simple buck converter is shown in
Figure 18.
Figure 18. Buck converter input model
As shown in Fig. 18, the internal DC input voltage source
.
3
2
I
o
Usually it is necessary to have several capacitors of the
same type in parallel to satisfy the ESR requirement.
The voltage ripple cause by the capacitor charge/
discharge should be an order of magnitude smaller than
the voltage ripple caused by the ESR. To guarantee this,
the capacitance should satisfy
.
R
f
2
10
C
esr
s
o
In many application circuits, several low ESR ceramic
capacitors are added in parallel with the aluminum
capacitors to further reduce ESR and improve high
frequency decoupling. Since the capacitances and the
ESR’s of ceramic and aluminum capacitors are different,
the following remarks are made to clarify some practical
issues.
Remark 1:
High frequency ceramic capacitors may not
carry most of the ripple current. It also depends on the
capacitor value. Only when the capacitor value is set
properly, the effect of ceramic capacitor low ESR starts
to be significant.
For example, if a 10
μ
F, 4m
ceramic capacitor is
connected in parallel with 2x1500
μ
F, 90m
electrolytic
capacitors, the ripple current in the ceramic capacitor is
only about 42% of the current in the electrolytic
capacitors at the ripple frequency. If a 100
μ
F, 2m
ceramic capacitor is used, the ripple current in the
ceramic capacitor will be about 4.2 times of that in the
electrolytic capacitors. When two 100
μ
F, 2m
ceramic
capacitors are used, the current ratio increases to 8.3.
In this case most of the ripple current flows in the
ceramic decoupling capacitor. The ESR of the ceramic
capacitors will then determine the output ripple-voltage.
Remark 2:
The total equivalent capacitance of the filter
bank is not simply the sum of all the paralleled capacitors.
The total equivalent ESR is not simply the parallel
combination of all the individual ESR’s either. Instead
they should be calculated using the following formulae.
)
C
C
(
C
C
)
C
R
C
R
(
)
C
C
(
C
C
)
R
R
(
:
(
C
b
1
a
1
b
1
a
1
2
b
1
2
b
1
a
1
2
a
1
2
b
1
a
1
2
b
1
2
a
1
2
2
b
1
a
1
eq
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| SC2441AEVB | 1.8V to 20V Input 2-Phase Synchronous Step-down Controllers with Step-up Converter |
| SC2441ATETRT | 1.8V to 20V Input 2-Phase Synchronous Step-down Controllers with Step-up Converter |
| SC2441 | Very Low Input Voltage 2-Phase Synchronous Step-down Controllers with Step-up Converter |
| SC2441EVB | Very Low Input Voltage 2-Phase Synchronous Step-down Controllers with Step-up Converter |
| SC2441ITSTRT | Very Low Input Voltage 2-Phase Synchronous Step-down Controllers with Step-up Converter |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| SC2441A_09 | 制造商:SEMTECH 制造商全稱:Semtech Corporation 功能描述:1.8V to 20V Input 2-Phase Synchronous Step-down Controllers with Step-up Converter |
| SC2441AEVB | 制造商:SEMTECH 制造商全稱:Semtech Corporation 功能描述:1.8V to 20V Input 2-Phase Synchronous Step-down Controllers with Step-up Converter |
| SC2441ATETRT | 制造商:Semtech Corporation 功能描述: |
| SC2441EVB | 制造商:SEMTECH 制造商全稱:Semtech Corporation 功能描述:Very Low Input Voltage 2-Phase Synchronous Step-down Controllers with Step-up Converter |
| SC2441ITSTRT | 制造商:Semtech Corporation 功能描述:Controller IC |
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