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PDF LT1578 Data sheet ( Hoja de datos )
| Número de pieza | LT1578 | |
| Descripción | 1.5A/ 200kHz Step-Down Switching Regulator | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de LT1578 (archivo pdf) en la parte inferior de esta página. Total 28 Páginas | ||
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FEATURES
s 1.5A Switch Current
s High Efficiency—Low Loss 0.2Ω Switch
s Constant 200kHz Switching Frequency
s 4V to 15V Input VoltageRange
s Minimum Output: 1.21V
s Low Supply Current: 1.9mA
s Low Shutdown Current: 20µA
s Easily Synchronizable Up to 400kHz
s Cycle-by-Cycle Current Limit
s Reduced EMI Generation
s Low Thermal Resistance SO-8 Package
s Uses Small Low Value Inductors
U
APPLICATIO S
s Portable Computers
s Battery-Powered Systems
s Battery Chargers
s Distributed Power Systems
LT1578/LT1578-2.5
1.5A, 200kHz Step-Down
Switching Regulator
DESCRIPTIO
The LT®1578 is a 200kHz monolithic buck mode switching
regulator. A 1.5A switch is included on the die along with
all the necessary oscillator, control and logic circuitry. The
topology is current mode for fast transient response and
good loop stability. The LT1578 is a modified version of the
LT1507 that has been optimized for noise sensitive appli-
cations. It will operate over a 4V to 15V input range.
In addition, the reference voltage has been lowered to al-
low the device to produce output voltages down to 1.2V.
Quiescent current has been reduced by a factor of two.
Switch on resistance has been reduced by 30%. Switch tran-
sition times have been slowed to reduce EMI generation.
The oscillator frequency has been reduced to 200kHz to
maintain high efficiency over a wide output current range.
The pinout has been changed to improve PC layout by al-
lowing the high current, high frequency switching circuitry
to be easily isolated from low current, noise sensitive con-
trol circuitry. The new SO-8 package includes a fused
ground lead that significantly reduces the thermal resistance
of the device to extend the ambient operating temperature
range. Standard surface mount external parts can be used
including the inductor and capacitors.
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATION
INPUT
5V TO 15V C3* +
10µF TO
50µF
3.3V Buck Converter
C2
0.33µF
VIN BOOST
VSW
LT1578
L1**
15µH
D2
1N914
OUTPUT**
3.3V, 1.25A
OPEN = ON
SHDN
GND
* RIPPLE CURRENT RATING ≥ IOUT/2
** INCREASE L1 TO 30µH FOR LOAD
CURRENTS ABOVE 0.6A AND TO
60µH ABOVE 1A
SEE APPLICATIONS INFORMATION
FB
VC
CC
100pF
D1
1N5818
R1
8.66k
R2 +
4.99k
C1
100µF, 10V
SOLID
TANTALUM
1578 TA01
Efficiency vs Load Current
90
85
80
75
70
65
60
55
50
0
VOUT = 3.3V
VIN = 5V
L = 25µH
0.25 0.50 0.75 1.00
LOAD CURRENT (A)
1.25 1.50
1578 TA02
1
1 page  
TYPICAL PERFORMANCE CHARACTERISTICS
LT1578/LT1578-2.5
Switching Frequency
240
220
Switch Current Limit Foldback
3.0
2.5
2.0
Minimum Input Voltage to Start
with 3.3V Output
4.50
4.25
200 1.5 4.00
1.0
180 3.75
0.5
160
–50 –25 0 25 50 75 100 125
JUNCTION TEMPERATURE (°C)
1576 G13
Maximum Output Current
at VOUT = 5V
1.6
L = 60µH
1.4
1.2 L = 30µH
1.0 L = 15µH
0.8
0.6
0.4
0.2
0
6 9 12 15
INPUT VOLTAGE (V)
1578 G15
BOOST Pin Current
30
0
0 0.2 0.4 0.6 0.8 1.0 1.2
FEEDBACK PIN VOLTAGE (V)
1578 G19
3.50
1
10 100
LOAD CURRENT (mA)
1000
1576 G14
Maximum Output Current
at VOUT = 3.3V
1.6
L = 60µH
1.4
L = 30µH
1.2
1.0 L = 15µH
Maximum Output Current
at VOUT = 2.5V
1.6
L = 60µH
1.4
L = 30µH
1.2
L = 15µH
1.0
0.8 0.8
0.6 0.6
0.4 0.4
0.2 0.2
0
4 6 8 10 12 14
INPUT VOLTAGE (V)
1578 G16
0
46
8 10 12 14
INPUT VOLTAGE (V)
1578 G17
VC Pin Shutdown Threshold
1.0
25
0.8
20
0.6
15
0.4
10
0.2
5
0
0 0.25 0.50 0.75 1.00 1.25 1.50
SWITCH CURRENT (A)
1576 G20
Kool Mµ is a registered trademark of Magnetics, Inc.
Metglas is a registered trademark of AlliedSignal, Inc.
0
–50 –25 0 25 50 75 100
JUNCTION TEMPERATURE (°C)
125
1576 G21
5
5 Page 
LT1578/LT1578-2.5
APPLICATIONS INFORMATION
(()( )( ) )IPEAK
=
IOUT
+
VOUT
2
VIN
fL
− VOUT
VIN
VIN = Maximum input voltage
f = Switching frequency, 200kHz
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 1) 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 1
VENDOR/
PART NO.
SERIES CORE
VALUE DC CORE RESIS- MATER- HEIGHT
(µH) (Amps) TYPE TANCE(Ω) IAL (mm)
Coiltronics
CTX15-2
15 1.7 Tor 0.059 KMµ 6.0
CTX33-2
33 1.4 Tor 0.106 KMµ 6.0
CTX68-4
68 1.2 Tor 0.158 KMµ 6.4
CTX15-1P
15 1.4 Tor 0.087 52 4.2
CTX33-2P
33 1.3 Tor 0.126 52 6.0
CTX68-4P
68 1.1 Tor 0.238 52 6.4
Sumida
CDRH74-150 15 1.47 SC 0.081 Fer 4.5
CDH115-330 33 1.68 SC 0.082 Fer 5.2
CDRH125-680 68 1.5 SC 0.12 Fer 6
CDH74-330
33 1.45 SC 0.17 Fer 5.2
Coilcraft
DO3308P-153 15 2 SC 0.12 Fer 3
DO3316P-333 33 2 SC 0.1
Fer 5.21
DO3316P-683 68 1.4 SC 0.18
Fer 5.21
Pulse
PE-53602
35 1.4 Tor 0.166 Fer 9.1
PE-53604
73 1.3 Tor 0.290 Fer 9.1
PE-53632
22 2.7 Tor 0.063 Fer 9.1
PE-53633
40 2.7 Tor 0.085 Fer
10
Gowanda
SMP3316-152K 15 3.5 SC 0.041 Fer
6
SMP3316-332K 33 2.3 SC 0.092 Fer
6
SMP3316-682K 68 1.7 SC 0.178 Fer
6
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 LT1578.PDF ] | |
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