|
|
PDF LT1576IS8-5SYNC Data sheet ( Hoja de datos )
| Número de pieza | LT1576IS8-5SYNC | |
| Descripción | 1.5A/ 200kHz Step-Down Switching Regulator | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
|
Hay una vista previa y un enlace de descarga de LT1576IS8-5SYNC (archivo pdf) en la parte inferior de esta página. Total 28 Páginas | ||
|
No Preview Available !
FEATURES
s Constant 200kHz Switching Frequency
s 1.21V Reference Voltage
s Fixed 5V Output Option
s Easily Synchronizable
s Uses All Surface Mount Components
s Inductor Size Reduced to 15µH
s Saturating Switch Design: 0.2Ω
s Effective Supply Current: 1.16mA
s Shutdown Current: 20µA
s Cycle-by-Cycle Current Limiting
s Fused Lead SO-8 Package
U
APPLICATIO S
s Portable Computers
s Battery-Powered Systems
s Battery Charger
s Distributed Power
LT1576/LT1576-5
1.5A, 200kHz Step-Down
Switching Regulator
DESCRIPTIO
The LT®1576 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 LT1576 is a modified version of the
industry standard LT1376 optimized for noise sensitive
applications.
In addition, the reference voltage has been lowered to
allow 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
allowing the high current high frequency switching cir-
cuitry to be easily isolated from low current noise sensitive
control circuitry. The new SO-8 package includes a fused
ground lead which significantly reduces the thermal resis-
tance of the device to extend the ambient operating tem-
perature range. There is an optional function of shutdown
or synchronization. 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
5V Buck Converter
INPUT
6V TO 25V C3* +
10µF TO
50µF
C2
0.33µF
VIN BOOST
VSW
LT1576 BIAS
L1**
15µH
D2
1N914
OUTPUT**
5V, 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
15.8k
R2 +
4.99k
C1
100µF, 10V
SOLID
TANTALUM
1576 TA01
Efficiency vs Load Current
100
VOUT = 5V
95
VIN = 10V
L = 33µH
90
85
80
75
70
0
0.25 0.50 0.75 1.00
LOAD CURRENT (A)
1.25 1.50
1576 TA02
1
1 page  
TYPICAL PERFORMANCE CHARACTERISTICS
LT1576/LT1576-5
Shutdown Supply Current
100
75
VIN = 25V
VIN = 10V
50
25
0
0 0.1 0.2 0.3 0.4
SHUTDOWN VOLTAGE (V)
1576 G10
Switching Frequency
240
220
Error Amplifier Transconductance
1600
1400
1200
1000
800
600
400
200
0
–50 –25 0 25 50 75 100 125
JUNCTION TEMPERATURE (°C)
1576 G11
Minimum Input Voltage
at VOUT = 5V
7
VOUT = 5V
MINIMUM
STARTING VOLTAGE
200 6
MINIMUM
RUNNING VOLTAGE
180
Frequency Foldback
250
SWITCHING FREQUENCY
200
150
100
50
FEEDBACK PIN CURRENT
0
0 0.5 1.0 1.5 2.0
FEEDBACK VOLTAGE (V)
1576 G12
Maximum Load Current
at VOUT = 10V
1.50
VOUT = 10V
L = 60µH
1.25
L = 30µH
1.00
L = 15µH
0.75
0.50
0.25
160
–50 –25 0 25 50 75 100
JUNCTION TEMPERATURE (°C)
125
1576 G13
Maximum Load Current
at VOUT = 5V
1.50
L = 60µH
1.25
L = 30µH
1.00 L = 15µH
0.75
0.50
0.25
VOUT = 5V
0
05
10 15
INPUT VOLTAGE (V)
20
25
1576 G16
50
1
10 100 1000
05
10 15 20 25
LOAD CURRENT (mA)
INPUT VOLTAGE (V)
1576 G14
1576 G15
Maximum Load Current
at VOUT = 3.3V
1.50
1.25
L = 60µH
L = 30µH
1.00 L = 15µH
0.75
0.50
0.25
VOUT = 3.3V
0
0 5 10 15
INPUT VOLTAGE (V)
20
25
1576 G17
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
PERMALLOY
0.01
CORE LOSS IS
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
1576 G18
Kool Mµ is a registered trademark of Magnetics, Inc.
5
5 Page 
LT1576/LT1576-5
APPLICATIONS INFORMATION
IOUT(MAX) =
( ) ( )( )( )Discontinuous mode
2
IP f L VIN
( )( )2 VOUT VIN − VOUT
Example: with L = 5µH, VOUT = 5V, and VIN(MAX) = 15V,
( ) ( )( ) ( )( )IOUT MAX
=
1.5
2
200
•
103
5
•10−6
15
2 5 15 − 5
= 0.34A
The main reason for using such a tiny inductor is that it is
physically very small, but keep in mind that peak-to-peak
inductor current will be very high. This will increase output
ripple voltage. If the output capacitor has to be made larger
to reduce ripple voltage, the overall circuit could actually
wind up larger.
CHOOSING THE INDUCTOR AND OUTPUT CAPACITOR
For most applications the output inductor will fall in the
range of 15µH to 60µH. Lower values are chosen to reduce
physical size of the inductor. Higher values allow more
output current because they reduce peak current seen by
the LT1576 switch, which has a 1.5A limit. Higher values
also reduce output ripple voltage, and reduce core loss.
Graphs in the Typical Performance Characteristics section
show maximum output load current versus inductor size
and input voltage. A second graph shows core loss versus
inductor size for various core materials.
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 LT1576 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 1.5A overload condition.
Dead shorts will actually be more gentle on the induc-
tor because the LT1576 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.
(()( )( ) )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 2) which meets the require-
ments 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 tempera-
ture operation will increase cost, sometimes dramati-
cally. Get a quote on the cheapest unit first to calibrate
yourself on price, then ask for what you really want.
11
11 Page | ||
| Páginas | Total 28 Páginas | |
| PDF Descargar | [ Datasheet LT1576IS8-5SYNC.PDF ] | |
Hoja de datos destacado
| Número de pieza | Descripción | Fabricantes |
| LT1576IS8-5SYNC | 1.5A/ 200kHz Step-Down Switching Regulator | Linear Technology |
| Número de pieza | Descripción | Fabricantes |
| SLA6805M | High Voltage 3 phase Motor Driver IC. |
 Sanken |
| SDC1742 | 12- and 14-Bit Hybrid Synchro / Resolver-to-Digital Converters. |
 Analog Devices |
|
DataSheet.es es una pagina web que funciona como un repositorio de manuales o hoja de datos de muchos de los productos más populares, |
| DataSheet.es | 2020 | Privacy Policy | Contacto | Buscar |