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PDF LTC3631 Data sheet ( Hoja de datos )
| Número de pieza | LTC3631 | |
| Descripción | High Voltage 100mA Synchronous Step-Down Converter | |
| Fabricantes | Linear Technology Corporation | |
| Logotipo |  |
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LTC3631
High Efficiency, High Voltage
100mA Synchronous
Step-Down Converter
FEATURES
DESCRIPTION
n Wide Input Voltage Range: Operation from 4.5V to 45V
n Overvoltage Lockout Provides Protection Up to 60V
n Internal High Side and Low Side Power Switches
n No Compensation Required
n 100mA Output Current
n Low Dropout Operation: 100% Duty Cycle
n Low Quiescent Current: 12μA
n 0.8V ±1% Feedback Voltage Reference
n Adjustable Peak Current Limit
n Internal and External Soft-Start
n Precise RUN Pin Threshold with Adjustable
Hysteresis
n 3.3V, 5V and Adjustable Output Versions
n Only Three External Components Required for Fixed
Output Versions
n Low Profile (0.75mm) 3mm × 3mm DFN and
Thermally-Enhanced MS8E Packages
APPLICATIONS
n 4mA to 20mA Current Loops
n Industrial Control Supplies
n Distributed Power Systems
n Portable Instruments
n Battery-Operated Devices
n Automotive Power Systems
The LTC®3631 is a high efficiency step-down DC/DC
converter with internal high side and synchronous power
switches that draws only 12μA typical DC supply current
at no load while maintaining output voltage regulation.
The LTC3631 can supply up to 100mA load current and
features a programmable peak current limit that provides
a simple method for optimizing efficiency in lower current
applications. The LTC3631’s combination of Burst Mode®
operation, integrated power switches, low quiescent cur-
rent, and programmable peak current limit provides high
efficiency over a broad range of load currents.
With its wide 4.5V to 45V input range and internal
overvoltage monitor capable of protecting the part through
60V surges, the LTC3631 is a robust converter suited for
regulating a wide variety of power sources. Additionally,
the LTC3631 includes a precise run threshold and soft-start
feature to guarantee that the power system start-up is
well-controlled in any environment.
The LTC3631 is available in the thermally enhanced
3mm × 3mm DFN and MS8E packages.
L, LT, LTC, LTM, Burst Mode, Linear Technology and the Linear logo are registered trademarks
of Linear Technology Corporation. All other trademarks are the property of their respective
owners.
TYPICAL APPLICATION
5V, 100mA Step-Down Converter
VIN
5V TO 45V
2.2μF
VIN SW
LTC3631-5
RUN
HYST
VOUT
SS
ISET
GND
100μH
3631 TA01a
VOUT
5V
10μF 100mA
Efficiency and Power Loss vs Load Current
100
90
EFFICIENCY
1000
80
70 100
60
POWER LOSS
50 10
40
30
20
0.1
VIN = 12V 1
VIN = 36V
1 10
LOAD CURRENT (mA)
100
3631 TA01b
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TYPICAL PERFORMANCE CHARACTERISTICS
LTC3631
Peak Current Trip Threshold
vs RISET
240
220 VIN = 10V
200
180
160
140
120
100
80
60
40
20
0
200 400 600 800 1000 1200
RISET (kΩ)
3631 G10
Quiescent Supply Current
vs Temperature
14
VIN = 10V
12
SLEEP
10
8
6
4 SHUTDOWN
2
0
–40 –10 20 50 80
TEMPERATURE (°C)
110
3631 G13
Switch Leakage Current
vs Temperature
0.6
VIN = 45V
0.5
0.4
0.3
0.2
0.1
0
–40
SW = 0V
SW = 45V
–10 20 50 80
TEMPERATURE (°C)
110
3631 G16
Peak Current Trip Threshold
vs Input Voltage
250
225 ISET OPEN
200
175
150
125 RSET = 500k
100
75
ISET = GND
50
25
0
0 5 10 15 20 25 30 35 40 45 50
INPUT VOLTAGE (V)
3631 G11
Quiescent Supply Current
vs Input Voltage
14
12
SLEEP
10
8
6
SHUTDOWN
4
2
0
5 15 25 35
VIN VOLTAGE (V)
Switch On-Resistance
vs Input Voltage
4.5
4.0
3.5
3.0 TOP
2.5
2.0
BOTTOM
1.5
1.0
0.5
0
0 10 20 30
VIN VOLTAGE (V)
40 50
3631 G14
Switch On-Resistance
vs Temperature
5 VIN = 10V
4
TOP
3
BOTTOM
2
1
0
–40 –10 20 50 80
TEMPERATURE (°C)
RUN Comparator Thresholds
vs Temperature
1.300
1.250
RISING
Operating Waveforms
SWITCH
VOLTAGE
20V/DIV
1.200
1.150
1.100
1.050
FALLING
OUTPUT
VOLTAGE
50mV/DIV
INDUCTOR
CURRENT
100mA/DIV
45
3631 G12
110
3631 G15
1.000
–40
–10 20 50 80
TEMPERATURE (°C)
110
3631 G17
VIN = 36V
VOUT = 5V
20μs/DIV
3631 G18
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LTC3631
APPLICATIONS INFORMATION
700 VOUT = 5V
600 ISET OPEN
L = 47μH
500
L = 100μH
400
300
L = 220μH
200
L = 470μH
100
0
5 10 15 20 25 30 35 40 45
VIN INPUT VOLTAGE (V)
3631 F02
Figure 2. Switching Frequency for VOUT = 5V
500
450
L = 47μH
400
350
VOUT = 3.3V
ISET OPEN
300 L = 100μH
250
200
150 L = 220μH
100 L = 470μH
50
0
5 10 15 20 25 30 35 40 45
VIN INPUT VOLTAGE (V)
3631 F03
Figure 3. Switching Frequency for VOUT = 3.3V
10000
1000
100
10
10
100 1000
PEAK INDUCTOR CURRENT (mA)
3631 F04
Figure 4. Recommended Inductor Values for Maximum Efficiency
where board area is not a limiting factor, inductors with
larger cores can be used, which extends the recommended
range of Figure 4 to larger values.
Inductor Core Selection
Once the value for L is known, the type of inductor must
be selected. High efficiency converters generally cannot
afford the core loss found in low cost powdered iron cores,
forcing the use of the more expensive ferrite cores. Actual
core loss is independent of core size for a fixed inductor
value but is very dependent of the inductance selected.
As the inductance increases, core losses decrease. Un-
fortunately, increased inductance requires more turns of
wire and therefore copper losses will increase.
Ferrite designs have very low core losses and are pre-
ferred at high switching frequencies, so design goals can
concentrate on copper loss and preventing saturation.
Ferrite core material saturates “hard,” which means that
inductance collapses abruptly when the peak design current
is exceeded. This results in an abrupt increase in inductor
ripple current and consequently output voltage ripple. Do
not allow the core to saturate!
Different core materials and shapes will change the
size/current and price/current relationship of an inductor.
Toroid or shielded pot cores in ferrite or permalloy ma-
terials are small and do not radiate energy but generally
cost more than powdered iron core inductors with similar
characteristics. The choice of which style inductor to use
mainly depends on the price vs size requirements and any
radiated field/EMI requirements. New designs for surface
mount inductors are available from Coiltronics, Coilcraft,
TDK, Toko, Sumida and Vishay.
CIN and COUT Selection
The input capacitor, CIN, is needed to filter the trapezoidal
current at the source of the top high side MOSFET. To
prevent large ripple voltage, a low ESR input capacitor
sized for the maximum RMS current should be used.
Approximate RMS current is given by:
IRMS
= IOUT(MAX)
•
VOUT
VIN
•
VIN − 1
VOUT
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11 Page | ||
| Páginas | Total 20 Páginas | |
| PDF Descargar | [ Datasheet LTC3631.PDF ] | |
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