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參數(shù)資料
| 型號： | ML4880 |
| 廠商： | Fairchild Semiconductor Corporation |
| 英文描述： | Portable PC/PCMCIA Power Controller(便攜式PC/PCMCIA電源控制器) |
| 中文描述： | 便攜式電腦/ PCMCIA的電源控制器（便攜式電腦/電源控制器的PCMCIA） |
| 文件頁數(shù)： | 7/15頁 |
| 文件大?。?/td> | 164K |
| 代理商： | ML4880 |
ML4880
7
DESIGN CONSIDERATIONS
A typical design can be implemented by using the
following design procedure. Note that this procedure is
not intended to give final values, but to give a good
starting point, and provide the relationships necessary to
make trade-off decisions. Some experimentation will be
necessary to optimize values and to verify that the design
operates over worst case conditions.
DESIGN SPECIFICATIONS
It is important to start with a clear definition of the design
specifications. Make sure the specifications reflect worst
case conditions. Key specifications include the minimum
and maximum input voltage and the output voltage and
load current for each output.
BUCK REGULATORS - INDUCTOR AND SENSE
RESISTOR SELECTION
Figure 6 shows the inductor current of the step down
regulators. The inductor current is made up of two
components: the DC current level set by the
transconductance amplifier, I
SENSE
, and the inductor ripple
current,
I
L
. The figure also shows that I
OUT
is the
summation of I
SENSE
and
1
/
2
I
L
:
I
I
I
V
R
T
V
2
V
L
OUT
SENSE
L
SENSE
SENSE
ON
IN
×
OUT
=
+
=
+
×
1
2
(
)
(3)
Therefore, the selection of the inductance value
determines how much of the output current is made up of
the ripple current. Higher inductor ripple current allows
smaller inductor values, but results in higher peak
currents, lower efficiency, and higher output voltage
ripple.
Inductor ripple currents in the range of 30% to 70% of the
maximum output current are typical. As a good starting
point set the inductor ripple current to 50% of the
maximum output current:
I
T
V
(
V
L
F
I
L
ON
IN
OUT
IRC
OUT MAX
(
=
×
=
×
)
)
(4)
where F
IRC
= ratio of inductor ripple current to the
maximum output current, or:
L
T
V
I
OUT MAX
V
ON
0 5
IN
OUT
=
×
×
(
)
.
(
)
(5)
Calculate the inductance using the volt-seconds value
given in Figure 5 at the maximum input voltage. Choose
the nearest standard value, realizing the trade-offs
mentioned before. Then, using the inductance value
chosen, determine the actual inductor ripple current at the
maximum and minimum input voltage using Equation 4
and Figure 5.
The sense resistor value can be determined using the
inductor ripple current value calculated above and
Equation 3 rearranged as follows:
R
V
I
I
I
I
SENSE
SENSE MIN
)
OUT MAX
(
L MIN
(
OUT MAX
(
L MIN
(
=
=
(
)
)
)
)
.
1
2
0 14
1
2
(6)
18
16
14
12
10
8
6
4
2
T
O
μ
s
V
IN
(V)
0
5
10
15
20
5V BUCK
3.3V BUCK
12V FLYBACK
Figure 4. T
ON
vs. V
IN
45
40
35
30
25
20
15
10
50
5
10
V
IN
(V)
V
μ
s
15
20
12V FLYBACK
3.3V BUCK
5V BUCK
Figure 5. Volt-seconds vs V
IN
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| ML4880CS | 制造商:MICRO-LINEAR 制造商全稱:MICRO-LINEAR 功能描述:Portable PC/PCMCIA Power Controller |
| ML4880ES | 制造商:MICRO-LINEAR 制造商全稱:MICRO-LINEAR 功能描述:Portable PC/PCMCIA Power Controller |
| ML4890 | 制造商:MICRO-LINEAR 制造商全稱:MICRO-LINEAR 功能描述:High Efficiency, Low Ripple Boost Regulator |
| ML4890CS-3 | 制造商:MICRO-LINEAR 制造商全稱:MICRO-LINEAR 功能描述:High Efficiency, Low Ripple Boost Regulator |
| ML4890CS-5 | 制造商:MICRO-LINEAR 制造商全稱:MICRO-LINEAR 功能描述:High Efficiency, Low Ripple Boost Regulator |
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