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PDF LTC3632 Data sheet ( Hoja de datos )
| Número de pieza | LTC3632 | |
| Descripción | High Voltage 20mA Synchronous Step-Down Converte | |
| Fabricantes | Linear Technology Corporation | |
| Logotipo |  |
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LTC3632
High Efficiency, High Voltage
20mA Synchronous
Step-Down Converter
FEATURES
n Wide Input Voltage Range: Operation from
4.5V to 50V
n Overvoltage Lockout Provides Protection Up to 60V
n Internal High Side and Low Side Power Switches
n No Compensation Required
n 20mA Output Current
n Low Dropout Operation: 100% Duty Cycle
n Low Quiescent Current: 12μA
n Wide Output Voltage Range: 0.8V to VIN
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 Few External Components Required
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
DESCRIPTION
The LTC®3632 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 LTC3632 can supply up to 20mA load current and
features a programmable peak current limit that provides
a simple method for optimizing efficiency in lower current
applications. The LTC3632’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 50V input range and internal
overvoltage monitor capable of protecting the part through
60V surges, the LTC3632 is a robust converter suited for
regulating a wide variety of power sources. Additionally,
the LTC3632 includes a precise run threshold and soft-start
feature to guarantee that the power system start-up is
well-controlled in any environment.
The LTC3632 is available in the thermally enhanced
3mm × 3mm DFN and MS8E packages.
L, LT, LTC, LTM and Burst Mode are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
TYPICAL APPLICATION
VIN
5V TO 50V
1μF
5V, 20mA Step-Down Converter
VIN SW
LTC3632
RUN
HYST
VFB
ISET SS
GND
1mH
1.47M
280k
3632 TA01a
VOUT
5V
10μF 20mA
Efficiency and Power Loss vs Load Current
100
90
EFFICIENCY
80
1000
70 100
60
50
POWER LOSS
40
10
30
20
0.1
VIN = 10V 1
VIN = 48V
1
LOAD CURRENT (mA)
10
3632 TA01b
3632f
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TYPICAL PERFORMANCE CHARACTERISTICS
LTC3632
Peak Current Trip Threshold
vs RISET
60
VIN = 10V
50
40
30
20
10
0
0 200 400 600 800 1000 1200
RISET (kΩ)
3632 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)
Switch Leakage Current
vs Temperature
0.30
VIN = 50V
0.25
110
3632 G13
0.20
0.15
0.10
SW = 50V
0.05 SW = 0V
0
–40
–10 20 50 80
TEMPERATURE (°C)
110
3632 G16
Peak Current Trip Threshold
vs Input Voltage
60
VIN = 10V
50
ISET OPEN
40
30
RSET = 500k
20
ISET = GND
10
Quiescent Supply Current
vs Input Voltage
14
12
SLEEP
10
8
6
4 SHUTDOWN
2
0
0 5 10 15 20 25 30 35 40 45 50
INPUT VOLTAGE (V)
3632 G11
0
5 15 25 35
INPUT VOLTAGE (V)
Switch On-Resistance
vs Input Voltage
8
7
6
TOP
5
4
3
BOTTOM
2
1
0 10 20 30 40 50
INPUT VOLTAGE (V)
3632 G14
Switch On-Resistance
vs Temperature
8
VIN = 10V
7
6
TOP
5
4
BOTTOM
3
2
1
0
–40 –10 20 50 80
TEMPERATURE (°C)
RUN Comparator Thresholds
vs Temperature
1.30
1.25 RISING
1.20
1.15
FALLING
1.10
1.05
Operating Waveforms
SWITCH
VOLTAGE
20V/DIV
OUTPUT
VOLTAGE
100mV/DIV
INDUCTOR
CURRENT
50mA/DIV
VIN = 48V
VOUT = 5V
20μs/DIV
45
3632 G12
110
3632 G15
3632 G18
1.00
–40
–10 20 50 80
TEMPERATURE (°C)
110
3632 G17
3632f
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LTC3632
APPLICATIONS INFORMATION
350 VOUT = 5V
300 ISET OPEN
L = 220μH
250
200 L = 470μH
150
100 L = 1000μH
50 L = 2200μH
0
5 10 15 20 25 30 35 40 45 50
VIN INPUT VOLTAGE (V)
3632 F02
Figure 2. Switching Frequency for VOUT = 5V
250 L = 220μH VOUT = 3.3V
ISET OPEN
200
150
L = 470μH
100
L = 1000μH
50
L = 2200μH
0
5 10 15 20 25 30 35 40 45 50
VIN INPUT VOLTAGE (V)
3632 F03
Figure 3. Switching Frequency for VOUT = 3.3V
10000
1000
100
10
PEAK INDUCTOR CURRENT (mA)
50
3632 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
3632f
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11 Page | ||
| Páginas | Total 20 Páginas | |
| PDF Descargar | [ Datasheet LTC3632.PDF ] | |
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