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PDF LT1374CS8-5SYNC Data sheet ( Hoja de datos )
| Número de pieza | LT1374CS8-5SYNC | |
| Descripción | 4.5A/ 500kHz Step-Down Switching Regulator | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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FEATURES
s Constant 500kHz Switching Frequency
s Easily Synchronizable
s Uses All Surface Mount Components
s Inductor Size Reduced to 1.8µH
s Saturating Switch Design: 0.07Ω
s Effective Supply Current: 2.5mA
s Shutdown Current: 20µA
s Cycle-by-Cycle Current Limiting
U
APPLICATIO S
s Portable Computers
s Battery-Powered Systems
s Battery Chargers
s Distributed Power
LT1374
4.5A, 500kHz Step-Down
Switching Regulator
DESCRIPTIO
The LT®1374 is a 500kHz monolithic buck mode switching
regulator. A 4.5A switch is included on the die along with
all the necessary oscillator, control and logic circuitry. High
switching frequency allows a considerable reduction in the
size of external components. The topology is current mode
for fast transient response and good loop stability. Both
fixed output voltage and adjustable parts are available.
A special high speed bipolar process and new design tech-
niques achieve high efficiency at high switching frequency.
Efficiency is maintained over a wide output current range
by using the output to bias the circuitry and by utilizing a
supply boost capacitor to saturate the power switch.
The LT1374 fits into standard 7-pin DD, TO-220 and fused
lead SO-8 packages. Full cycle-by-cycle short-circuit
protection and thermal shutdown are provided. Standard
surface mount external parts are used, including the
inductor and capacitors. There is the optional function of
shutdown or synchronization. A shutdown signal reduces
supply current to 20µA. Synchronization allows an exter-
nal logic level signal to increase the internal oscillator from
580kHz to 1MHz.
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATIO
5V Buck Converter
D2
1N914
INPUT
6V TO 25V C3* +
10µF TO
50µF
DEFAULT
= ON
C2
0.27µF
BOOST
VIN VSW
LT1374-5 BIAS
SHDN
GND
SENSE
VC
CC
1.5nF
L1**
5µH
D1 +
MBRS330T3
* RIPPLE CURRENT RATING ≥ IOUT/2
** INCREASE L1 TO 10µH FOR LOAD CURRENTS ABOVE 3.5A AND TO 20µH ABOVE 4A
SEE APPLICATIONS INFORMATION
OUTPUT**
5V, 4.25A
C1
100µF, 10V
SOLID
TANTALUM
1374 TA01
Efficiency vs Load Current
100
VOUT = 5V
VIN = 10V
95 L = 10µH
90
85
80
75
70
0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
LOAD CURRENT (A)
1374 TA02
1
1 page  
TYPICAL PERFORMANCE CHARACTERISTICS
Frequency Foldback
500
400
SWITCHING
FREQUENCY
300
200
100
0
0
FEEDBACK PIN
CURRENT
0.5 1.0 1.5 2.0
FEEDBACK PIN VOLTAGE (V)
2.5
1374 G10
Maximum Load Current
at VOUT = 10V
4.5
VOUT = 10V
L = 20µH
L = 10µH
4.0
L = 5µH
3.5
Switching Frequency
550
540
530
520
510
500
490
480
470
460
450
– 50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
1374 G11
Maximum Load Current
at VOUT = 3.3V
4.5
L = 20µH
L = 10µH
4.0 L = 5µH
3.5
LT1374
Minimum Input Voltage
with 5V Output
6.4
6.2
MINIMUM
6.0 STARTING
VOLTAGE
5.8
5.6 MINIMUM
RUNNING
5.4 VOLTAGE
5.2
5.0
1
10 100
LOAD CURRENT (mA)
1000
1374 G12
Maximum Load Current
at VOUT = 5V
4.5
L = 20µH
L = 10µH
4.0
L = 5µH
3.5
3.0
0
5 10 15 20
INPUT VOLTAGE (V)
25
1374 G13
BOOST Pin Current
100
DUTY CYCLE = 100%
90
80
70
60
50
40
30
20
10
0
0 12 34 5
SWITCH CURRENT (A)
1374 G16
Kool Mµ is a registered trademark of Magnetics, Inc.
VOUT = 3.3V
3.0
0
5
10 15
INPUT VOLTAGE (V)
20
25
1374 G14
VOUT = 5V
3.0
0
5
10 15
INPUT VOLTAGE (V)
20
25
1374 G15
VC Pin Shutdown Threshold
1.4
SHUTDOWN
1.2
1.0
0.8
0.6
0.4
–50
–25 0 25 50 75 100
JUNCTION TEMPERATURE (°C)
125
1374 G11
Inductor Core Loss
1.0
VOUT = 5V, VIN = 10V, IOUT = 1A
20
12
8
TYPE 52
4
0.1 POWDERED IRON 2
Kool Mµ®
1.2
0.8
0.01
CORE LOSS IS
PERMALLOY
µ = 125
INDEPENDENT OF LOAD
CURRENT UNTIL LOAD CURRENT FALLS
LOW ENOUGH FOR CIRCUIT TO GO INTO
DISCONTINUOUS MODE
0.001
0 5 10 15 20
INDUCTANCE (µH)
0.4
0.2
0.12
0.08
0.04
0.02
25
1374 G01
5
5 Page 
LT1374
APPLICATIONS INFORMATION
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.
(()( )( ) )IPEAK
=
IOUT
+
VOUT
2
VIN
fL
− VOUT
VIN
VIN = 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
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
saturation), average current (to limit heating), and fault
current (if the inductor gets too hot, wire insulation will
melt and cause turn-to-turn shorts). Keep in mind that
all good things like high efficiency, low profile, and high
temperature operation will increase cost, sometimes
dramatically. Get a quote on the cheapest unit first to
calibrate yourself on price, then ask for what you really
want.
5. After making an initial choice, consider the secondary
things like output voltage ripple, second sourcing, etc.
Use the experts in the Linear Technology’s applica-
tions department if you feel uncertain about the final
choice. They have experience with a wide range of
inductor types and can tell you about the latest devel-
opments in low profile, surface mounting, etc.
Table 2
VENDOR/
PART NO.
SERIES CORE
VALUE DC CORE RESIS- MATER- HEIGHT
(µH) (Amps) TYPE TANCE(Ω) IAL (mm)
Coiltronics
CTX2-1
2 4.1 Tor 0.011 KMµ 4.2
CTX5-4
5 4.4 Tor 0.019 KMµ 6.4
CTX8-4
8 3.5 Tor 0.020 KMµ 6.4
CTX2-1P
2 3.4 Tor 0.014 52 4.2
CTX2-3P
2 4.6 Tor 0.012 52 4.8
CTX5-4P
5 3.3 Tor 0.027 52 6.4
Sumida
CDRH125
10 4.0 SC 0.025
Fer
6
CDRH125
12 3.5 SC 0.027
Fer
6
CDRH125
15 3.3 SC 0.030
Fer
6
CDRH125
18 3.0 SC 0.034
Fer
6
Coilcraft
DT3316-222 2.2
5
SC 0.035
Fer
5.1
DT3316-332 3.3
5
SC 0.040
Fer
5.1
DT3316-472 4.7
3
SC 0.045
Fer
5.1
Pulse
PE-53650
4 4.8 Tor 0.017 Fer
9.1
PE-53651
5 5.4 Tor 0.018 Fer
9.1
PE-53652
9 5.5 Tor 0.022 Fer
10
PE-53653
16 5.1 Tor 0.032
Fer
10
Dale
IHSM-4825 2.7 5.1 Open 0.034 Fer 5.6
IHSM-4825 4.7 4.0 Open 0.047 Fer 5.6
IHSM-5832 10 4.3 Open 0.053 Fer 7.1
IHSM-5832 15 3.5 Open 0.078 Fer 7.1
IHSM-7832 22 3.8 Open 0.054 Fer 7.1
Tor = Toroid
SC = Semi-closed geometry
Fer = Ferrite core material
52 = Type 52 powdered iron core material
KMµ = Kool Mµ
11
11 Page | ||
| Páginas | Total 28 Páginas | |
| PDF Descargar | [ Datasheet LT1374CS8-5SYNC.PDF ] | |
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