LT1374IR Linear Technology, LT1374IR Datasheet - Page 11

• Manufacturer Part Number: LT1374IR
• Description: IC SW REG 4.5A ADJ STEP-DWN 7-DD
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LT1374IR

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 2.42 ~ 21.5 V
• Current - Output: 4.5A
• Frequency - Switching: 500kHz
• Voltage - Input: 5 ~ 25 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: D²Pak, TO-263 (7 leads + tab)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power - Output: -

APPLICATIONS
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
2. Calculate peak inductor current at full load current to
3. Decide if the design can tolerate an “open” core geom-
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.
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.
V
f = Switching frequency, 500kHz
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
IN
= Maximum input voltage
U
INFORMATION
U
W
U
4. Start shopping for an inductor (see representative
Table 2
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
KMµ = Kool Mµ
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.
surface mount units in Table 2) which meets the
requirements of core shape, peak current (to avoid
VALUE
(
2.2
3.3
4.7
2.7
4.7
µ
10
12
15
18
16
10
15
22
2
5
8
2
2
5
4
5
9
H)
(Amps)
4.1
4.4
3.5
3.4
4.6
3.3
4.0
3.5
3.3
3.0
4.8
5.4
5.5
5.1
5.1
4.0
4.3
3.5
3.8
DC
5
5
3
CORE
TYPE
Open
Open
Open
Open
Open
Tor
Tor
Tor
Tor
Tor
Tor
Tor
Tor
Tor
Tor
SC
SC
SC
SC
SC
SC
SC
TANCE(
SERIES
RESIS-
0.011
0.019
0.020
0.014
0.012
0.027
0.025
0.027
0.030
0.034
0.035
0.040
0.045
0.017
0.018
0.022
0.032
0.034
0.047
0.053
0.078
0.054
Ω
)
MATER- HEIGHT
CORE
KMµ
KMµ
KMµ
IAL
Fer
Fer
Fer
Fer
Fer
Fer
Fer
Fer
Fer
Fer
Fer
Fer
Fer
Fer
Fer
Fer
52
52
52
LT1374
11
(mm)
4.2
6.4
6.4
4.2
4.8
6.4
5.1
5.1
5.1
9.1
9.1
5.6
5.6
7.1
7.1
7.1
10
10
1374fd
6
6
6
6