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參數(shù)資料
| 型號(hào)： | SP6640 |
| 元件分類(lèi)： | DC/DC變換器 |
| 英文描述： | Adjustable, High Efficiency, Low I Q , Step-Down DC-DC Converter(3.3V或可調(diào)電壓，高效，低I Q，步降DC-DC變換器) |
| 中文描述： | 可調(diào)，高效率，低智商，降壓型DC - DC轉(zhuǎn)換器電壓（3.3V或可調(diào)電壓，高效，低智商，步降型DC - DC變換器） |
| 文件頁(yè)數(shù)： | 9/13頁(yè) |
| 文件大?。?/td> | 82K |
| 代理商： | SP6640 |
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Rev. 2/23/01 SP6639/40/53 5/ 3.3/ 3V, Adj High Efficiency, Low I
Q
Step-Down DC-DC Converter Copyright 2001 Sipex Corporation
P
Figure 4. Adjustable-Output Operation
Inductor Selection
When selecting an inductor, consider these four
factors: peak-current rating, inductance value,
series resistance, and size. It is important not to
exceed the inductor's peak-current rating. A
saturated inductor will pull excessive currents
through SP6639/40/53's switch, and may cause
damage. Avoid using RF chokes or air-core
inductors since they have very low peak-current
ratings. Electromagnetic interference must not
upset nearby circuitry or the regulator IC.
Recall that the inductance value determines
IPEAK for all input voltages (Equation 3). If
there are no resistive losses and the diode is
ideal, the maximum average current that can be
drawn from the SP6639/40/53 will be one-half
IPEAK. With the real losses in the switch,
inductor, and diode taken into account, the real
maximum output current typically varies from
90% to 50% of the ideal. The following steps
describe a conservative way to pick an appropri-
ate inductor.
Step 1: Decide on the maximum required output
current, in amperes:
IOUTMAX
Step 2: I
PEAK
= 4 X I
OUTMAX
Step 3: L = 50/I
PEAK
. L will be in
m
H. Do not
use an inductor of less than 100
m
H.
Step 4: Make sure that I
does not exceed
0.6A or the inductor’s maximum cur-
rent rating whichever is lower.
C
IN
100
μ
F
VFB
6
8
3
4
5
1
7
SP6639
+4.0INPUT
GND
SHDN
V+
LBI
R4
R3
1N5817
L = 100
μ
F
C
OUT
100
μ
F
OUTPUT
+
+
V
OUT
L
X
Inductor series resistance affects both efficiency
and dropout voltage. A high series resistance
severely limits the maximum current available
at lower input voltages. Output currents up to
225mA are possible if the inductor has low
series resistance. Inductor and series switch
resistance form an LR circuit during t
. If the
L/R time constant is less than the oscillator t
,
the inductor's peak-current will fall short of the
desired I
PEAK
.
To maximize efficiency, choose the highest-
value inductor that will provide the required
output current over the whole range of your
input voltage (see Typical Operating Character-
istics). Inductors with peak currents in the 600mA
range do not need to be very large. They are
about the size of a 1W resistor, with surface
mount versions less than 5mm in diameter.
Table 1 lists the suppliers of inductors suitable
for use with the SP6639/40/53.
Output Filter Capacitor
The SP6639/40/53 output ripple has two com-
ponents. One component results from the varia-
tion in stored charge on the filter capacitor with
each LX pulse. The other is the product of the
current into the capacitor and the capacitor’s
equivalent series resistance (ESR).
The amount of charge delivered in each oscilla-
tor pulse is determined by the inductor value and
input voltage. It decreases with larger induc-
tance, but increases as the input voltage lessens.
As a general rule, a smaller amount of charge
delivered in each pulse results in less output
ripple.
With low-cost aluminum electrolytic capaci-
tors, the ES-induced ripple can be larger than
that caused by the charge variation. Conse-
quently, high-quality aluminum-electrolytic or
tantalum filter capacitors should be considered
to minimize output ripple. Best results at
reasonable cost are typically achieved with an
aluminum-electrolytic capacitor in the 100
μ
F
range, in parallel with a 0.1
μ
F ceramic
capacitor (see Table 1).
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PDF描述 |
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| SP6653 | Adjustable, High Efficiency, Low I Q , Step-Down DC-DC Converter(3V或可調(diào)電壓，高效，低I Q，步降DC-DC變換器) |
| SP6641BEK-3.3 | Low Noise Evaluation Board |
| SP6641AEK-3.3 | Circular Connector; No. of Contacts:3; Series:MS27466; Body Material:Aluminum; Connecting Termination:Crimp; Connector Shell Size:9; Circular Contact Gender:Pin; Circular Shell Style:Wall Mount Receptacle; Insert Arrangement:9-98 RoHS Compliant: No |
| SP6641AEK-5.0 | Low Noise Evaluation Board |
| SP6641AKEB-3.3 | Circular Connector; No. of Contacts:4; Series:MS27484; Body Material:Aluminum; Connecting Termination:Crimp; Connector Shell Size:12; Circular Contact Gender:Socket; Circular Shell Style:Straight Plug; Insert Arrangement:12-4 RoHS Compliant: No |
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