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參數資料
| 型號： | UC3573D |
| 英文描述： | 2 step-down DC/DC converters / 5 LDO power management |
| 中文描述： | 電壓模式開關電源控制器 |
| 文件頁數： | 5/8頁 |
| 文件大小： | 208K |
| 代理商： | UC3573D |
2. Inductor Selection (L)
A. Preliminary Calculations
To select the inductor, the calculation of the following
three parameters is necessary:
Dmax, the maximum switch duty cycle (0
≤
D
≤
0.9):
D
max
=
V
OUT
+
V
F
V
INmin
V
OUT
+
V
F
0.6V
where typically V
F
= 0.5V for Schottky diodes and V
F
=
0.8V for fast recovery diodes.
E
T, the product of volts
time that charges the induc-
tor:
E
T
=
D
max
(
V
INmin
0.6V
)
10
6
52,000Hz
(
V
μ
s
)
I
IND, DC
, the average inductor current under full load:
I
IND,
DC
=
1.05
I
LOADmax
1
D
max
B. Identify Inductor Value:
1. From Figure 4, identify the inductor code for the region
indicated by the intersection of E
T and I
IND, DC
. This
code gives the inductor value in microhenries. The L or H
prefix signifies whether the inductor is rated for a maxi-
mum E
T of 90V
μ
s (L) or 250V
μ
s (H).
2. If D < 0.85, go to step C. If D
≥
0.85, calculate the
minimum inductance needed to ensure the switching
regulator’s stability:
0.3
0.4
0.45
0.35
0.5 0.6 0.7 0.8 0.9 1.0
1.5
2.0
2.5
3.0
20
30
35
25
40
45
50
60
70
80
90
100
200
150
L47
L68
L100
L150
L220
L330
H2200
L680
H1500
H1000
H680
H470
H330
H220
H150
L470
E
μ
s
I
IND, DC
(A)
Figure 4. Inductor Selection Graph
If L
min
is smaller than the inductor values found in step
B1, go on to step C. Otherwise, the inductor value found
in step B1 is too low; an appropriate inductor code
should be obtained from the graph as follows:
1.
Find the lowest value inductor that is greater than
L
min
.
Find where E
T intersects this inductor value to
determine if it has an L or H prefix. If E
T intersects
both the L and H regions, select the inductor with an
H prefix.
2.
C. Inductor Selection
Select an inductor from the table of Figure 5 which cross
references the inductor codes to the part numbers of the
three different manufacturers. The inductors listed in this
table have the following characteristics:
AIE(ferrite, pot-core inductors): Benefits of this type
are low etectromagnetic interference (EMI), small
physical size, and very low power dissipation (core
loss).
Pulse(powdered iron, toroid core inductors): Bene-
fits are low EMI and ability to withstand E
T and
peak current above rated value better than ferrite
cores.
Renco(ferrite, bobbin-core inductors): Benefits are
low cost and best ability to withstand E
T and peak
current above rated value. Be aware that these in-
ductors generate more EMI than the other types, and
this may interfere with signals sensitive to noise.
UC2577-ADJ
Note: This chart assumes that the inductor ripple current inductor is approximately 20% to 30% of the average inductor current
(when the regulator is under full load). Greater ripple current causes higher peak switch currents and greater output ripple volt-
age. Lower ripple current is achieved with larger value inductors. The factor of 20% to 30% is chosen as a convenient balance
between the two extremes.
APPLICATIONS INFORMATION (cont.)
5
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