參數(shù)資料
型號(hào)： SC2441
廠商： Semtech Corporation
英文描述： Very Low Input Voltage 2-Phase Synchronous Step-down Controllers with Step-up Converter
中文描述： 非常低的輸入電壓2相同步降壓與升壓轉(zhuǎn)換器控制器
文件頁(yè)數(shù)： 14/35頁(yè)
文件大小： 733K
代理商： SC2441
14
2005 Semtech Corp.
www.semtech.com
POWER MANAGEMENT
Applications Information (Cont.)
SC2441
conversion ratio at a given switching frequency. If the
desired output voltage requires high operating duty-cycle,
then operating frequency will have to be lowered to allow
modulating headroom.
Setting the Step-down Channel Frequency
The switching frequency of both step-down controllers is
set with an external resistor from Pin 10 to the ground.
The set frequency is inversely proportional to the resistor
value (Figure 5).
0
100
200
300
400
500
600
700
800
0
50
100
150
200
250
Rosc (k Ohm)
f
Figure 5. Step-down Channel Free-running frequency vs.
R
OSC
.
Inductor (L) and Ripple Current
Both step-down controllers in the SC2441 operate in
synchronous continuous-conduction mode (CCM) regardless
of the output load. The output inductor selection/design
is based on the output DC and transient requirements.
Both output current and voltage ripples are reduced with
larger inductors but it takes longer to change the inductor
current during load transients. Conversely smaller inductors
results in lower DC copper losses but the AC core losses
(flux swing) and the winding AC resistance losses are
higher. A compromise is to choose the inductance such
that
peak-to-peak inductor ripple-current
is 20% to 30% of
the rated output load current.
Assuming that the inductor current ripple (peak-to-peak)
is
δ
*
I
o
, the inductance will then be
.
f
I
)
D
1
o
δ
V
L
s
o
=
The peak current in the inductor becomes (1+
δ
/2)*Io
and the RMS current is
.
12
1
I
I
,
2
o
rms
δ
+
=
The followings are to be considered when choosing
inductors.
a) Inductor core material: For high efficiency applications
above 350KHz, ferrite, Kool-Mu and polypermalloy
materials should be used. Low-cost powdered iron cores
can be used for cost sensitive-applications below 350KHz
but with attendant higher core losses.
b) Select inductance value: Sometimes the calculated
inductance value is not available off-the-shelf. The designer
can choose the adjacent (larger) standard inductance
value. The inductance varies with temperature and DC
current. It is a good engineering practice to re-evaluate
the resultant current ripple at the rated DC output current.
c) Current rating: The saturation current of the inductor
should be at least 1.5 times of the peak inductor current
under all conditions.
Output Capacitor (C
o
) and V
out
Ripple
The output capacitor provides output current filtering in
steady state and serves as a reservoir during load transient.
The output capacitor can be modeled as an ideal capacitor
in series with its parasitic ESR (
R
esr
) and ESL (
L
esl
) (Figure
6).
Co
Lesl
Resr
Figure 6.
C
o
equivalent circuit
If the current through the branch is i
b
(t), the voltage across
the terminals will then be
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相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
SC2441A 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
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
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