參數(shù)資料
型號(hào)： 3745SN
廠商： Linear Technology Corporation
元件分類(lèi)： 基準(zhǔn)電壓源/電流源
英文描述： RADIATION HARDENED HIGH EFFICIENCY, 5 AMP SWITCHING REGULATORS
中文描述： 抗輻射高效，5安培開(kāi)關(guān)穩(wěn)壓器
文件頁(yè)數(shù)： 11/32頁(yè)
文件大?。?/td> 309K
代理商： 3745SN
11
LT1374
1374fb
When choosing an inductor you might have to consider
maximum load current, core and copper losses, allowable
component height, output voltage ripple, EMI, fault cur-
rent in the inductor, saturation, and of course, cost. The
following procedure is suggested as a way of handling
these somewhat complicated and conflicting requirements.
1. Choose a value in microhenries from the graphs of
maximum load current and core loss. Choosing a small
inductor may result in discontinuous mode operation
at lighter loads, but the LT1374 is designed to work
well in either mode. Keep in mind that lower core loss
means higher cost, at least for closed core geometries
like toroids. The core loss graphs show both absolute
loss and percent loss for a 5W output, so actual percent
losses must be calculated for each situation.
Assume that the average inductor current is equal to
load current and decide whether or not the inductor
must withstand continuous fault conditions. If maxi-
mum load current is 0.5A, for instance, a 0.5A inductor
may not survive a continuous 4.5A overload condition.
Dead shorts will actually be more gentle on the induc-
tor because the LT1374 has foldback current limiting.
2. Calculate peak inductor current at full load current to
ensure that the inductor will not saturate. Peak current
can be significantly higher than output current, espe-
cially with smaller inductors and lighter loads, so don’t
omit this step. Powdered iron cores are forgiving
because they saturate softly, whereas ferrite cores
saturate abruptly. Other core materials fall somewhere
in between. The following formula assumes continu-
ous mode of operation, but it errs only slightly on the
high side for discontinuous mode, so it can be used for
all conditions.
(
( )( )( )
I
I
V
V
V
f L V
PEAK
OUT
OUT
2
IN
OUT
IN
=
+
)
V
IN
= Maximum input voltage
f = Switching frequency, 500kHz
3. Decide if the design can tolerate an “open” core geom-
etry like a rod or barrel, with high magnetic field
radiation, or whether it needs a closed core like a toroid
to prevent EMI problems. One would not want an open
APPLICATIO
S I
N
FOR
ATIO
U
W
U
core next to a magnetic storage media, for instance!
This is a tough decision because the rods or barrels are
temptingly cheap and small and there are no helpful
guidelines to calculate when the magnetic field radia-
tion will be a problem.
4. Start shopping for an inductor (see representative
surface mount units in Table 2) which meets the
requirements of core shape, peak current (to avoid
Table 2
SERIES
RESIS-
TANCE(
)
CORE
MATER-
IAL
VENDOR/
PART NO.
Coiltronics
CTX2-1
CTX5-4
CTX8-4
CTX2-1P
CTX2-3P
CTX5-4P
Sumida
CDRH125
CDRH125
CDRH125
CDRH125
Coilcraft
DT3316-222
DT3316-332
DT3316-472
Pulse
PE-53650
PE-53651
PE-53652
PE-53653
Dale
IHSM-4825
IHSM-4825
IHSM-5832
IHSM-5832
IHSM-7832
Tor = Toroid
SC = Semi-closed geometry
Fer = Ferrite core material
52 = Type 52 powdered iron core material
KM
μ
= Kool M
μ
VALUE
(
μ
H)
DC
CORE
TYPE
HEIGHT
(mm)
(Amps)
2
5
8
2
2
5
4.1
4.4
3.5
3.4
4.6
3.3
Tor
Tor
Tor
Tor
Tor
Tor
0.011
0.019
0.020
0.014
0.012
0.027
KM
μ
KM
μ
KM
μ
52
52
52
4.2
6.4
6.4
4.2
4.8
6.4
10
12
15
18
4.0
3.5
3.3
3.0
SC
SC
SC
SC
0.025
0.027
0.030
0.034
Fer
Fer
Fer
Fer
6
6
6
6
2.2
3.3
4.7
5
5
3
SC
SC
SC
0.035
0.040
0.045
Fer
Fer
Fer
5.1
5.1
5.1
4
5
9
4.8
5.4
5.5
5.1
Tor
Tor
Tor
Tor
0.017
0.018
0.022
0.032
Fer
Fer
Fer
Fer
9.1
9.1
10
10
16
2.7
4.7
10
15
22
5.1
4.0
4.3
3.5
3.8
Open
Open
Open
Open
Open
0.034
0.047
0.053
0.078
0.054
Fer
Fer
Fer
Fer
Fer
5.6
5.6
7.1
7.1
7.1
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