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PDF LTC7138 Data sheet ( Hoja de datos )
| Número de pieza | LTC7138 | |
| Descripción | 140V 400mA Step-Down Regulator | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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Features
n Wide Operating Input Voltage Range: 4V to 140V
n Internal Low Resistance Power MOSFET
n No Compensation Required
n Adjustable 100mA to 400mA Maximum Output
Current
n Low Dropout Operation: 100% Duty Cycle
n Low Quiescent Current: 12µA
n Wide Output Range: 0.8V to VIN
n 0.8V ±1% Feedback Voltage Reference
n Precise RUN Pin Threshold
n Internal or External Soft-Start
n Programmable 1.8V, 3.3V, 5V or Adjustable Output
n Few External Components Required
n Programmable Input Overvoltage Lockout
n Thermally Enhanced High Voltage MSOP Package
Applications
n Industrial Control Supplies
n Medical Devices
n Distributed Power Systems
n Portable Instruments
n Battery-Operated Devices
n Avionics
n Automotive
LTC7138
High Efficiency, 140V
400mA Step-Down
Regulator
Description
The LTC®7138 is a high efficiency step-down DC/DC
regulator with internal power switch that draws only 12μA
typical DC supply current while maintaining a regulated
output voltage at no load.
The LTC7138 can supply up to 400mA load current and
features a programmable peak current limit that provides
a simple method for optimizing efficiency and for reduc-
ing output ripple and component size. The LTC7138’s
combination of Burst Mode® operation, integrated power
switch, low quiescent current, and programmable peak
current limit provides high efficiency over a broad range
of load currents.
With its wide input range of 4V to 140V and programmable
overvoltage lockout, the LTC7138 is a robust regulator
suited for regulating from a wide variety of power sources.
Additionally, the LTC7138 includes a precise run threshold
and soft-start feature to guarantee that the power system
start-up is well-controlled in any environment. A feedback
comparator output enables multiple LTC7138s to be con-
nected in parallel for higher current applications.
The LTC7138 is available in a thermally enhanced high
voltage-capable 16-lead MSE package with four missing pins.
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 to 140V Input to 5V Output, 400mA Step-Down Regulator
VIN
5V TO 140V CIN
1µF
250V
VIN SW
LTC7138
RUN ANODE
SS
VPRG1
VFB
VPRG2
OVLO
GND
L1
220µH
VOUT
5V
COUT 400mA
22µF
7138 TA01a
Efficiency and Power Loss vs Load Current
100
90 EFFICIENCY
80
70
60 1000
50
40 POWER LOSS
100
30
20
10
0
0.1
VIN = 12V 10
VIN = 48V
VIN = 140V 1
1 10 100 1000
LOAD CURRENT (mA)
7138 TA01b
For more information www.linear.com/LTC7138
7138f
1
1 page  
Typical Performance Characteristics
LTC7138
Quiescent Supply Current
vs Input Voltage
15
SLEEP
10
5
SHUTDOWN
0
0 30 60 90 120 150
VIN VOLTAGE (V)
7138 G10
Switch On-Resistance
vs Input Voltage
3.0
2.5
2.0
1.5
1.0
0
30 60 90 120 150
VIN VOLTAGE (V)
7138 G13
Quiescent Supply Current
vs Temperature
35
VIN = 140V
30
25
20
15 SLEEP
10
5
0
–55 –25
SHUTDOWN
5 35 65 95
TEMPERATURE (°C)
125 155
7138 G11
Switch Pin Current
vs Temperature
15 VIN = 140V
SLEEP MODE
10
SW = 0.8V
5 CURRENT INTO SW
0
SW = 0V
–5 CURRENT OUT OF SW
–10
–15
–55 –25
5 35 65 95
TEMPERATURE (°C)
125 155
7138 G12
Switch On-Resistance
vs Temperature
4 ISW = 250mA
3
2
1
Load Step Transient Response
OUTPUT
VOLTAGE
100mV/DIV
LOAD
CURRENT
200mA/DIV
VIN = 48V
200µs/DIV
VOUT = 3.3V
10mA TO 400mA LOAD STEP
FIGURE 14 CIRCUIT
7138 G15
0
–55 –25
5 35 65 95
TEMPERATURE (°C)
125 155
7138 G14
Operating Waveforms, VIN = 48V
OUTPUT
VOLTAGE
100mV/DIV
SWITCH
VOLTAGE
20V/DIV
INDUCTOR
CURRENT
500mA/DIV
VIN = 48V
10µs/DIV
VOUT = 3.3V
IOUT = 300mA
FIGURE 14 CIRCUIT
7138 G16
Operating Waveforms, VIN = 140V
OUTPUT
VOLTAGE
100mV/DIV
SWITCH
VOLTAGE
50V/DIV
INDUCTOR
CURRENT
500mA/DIV
VIN = 140V
10µs/DIV
VOUT = 3.3V
IOUT = 300mA
FIGURE 14 CIRCUIT
7138 G17
Short-Circuit and Recovery
OUTPUT
VOLTAGE
1V/DIV
INDUCTOR
CURRENT
500mA/DIV
500µs/DIV
FIGURE 14 CIRCUIT
7138 G18
For more information www.linear.com/LTC7138
7138f
5
5 Page 
LTC7138
Applications Information
board area and saturation current requirements yields the
highest efficiency in most LTC7138 applications.
A good first choice for the inductor can be calculated
based on the maximum operating input voltage and the
ISET pin resistor. If the ISET pin is shorted to ground or
left open, use 50k or 200k respectively for RISET in the
following equation.
L
=
220µH •
VIN(MAX )
150V
•
200kΩ
RISET
An additional constraint on the inductor value is the
LTC7138’s 150ns minimum switch on-time. Therefore, in
order to avoid excessive overshoot in the inductor current,
the inductor value must be chosen so that it is larger than
a minimum value which can be computed as follows:
L
>
VIN(MAX )
IPEAK
• 150ns
• 0.3
• 1.2
where VIN(MAX) is the maximum input supply voltage
when switching is enabled, IPEAK is the peak current, and
the factor of 1.2 accounts for typical inductor tolerance
and variation over temperature. With the ISET pin open,
this minimum inductor value is approximately equal to
VIN(MAX) • 1µH/V.
Although the previous equation provides a minimum in-
ductor value, higher efficiency is typically achieved with a
larger inductor value, which produces a lower switching
frequency. The recommended range of inductor values
for small surface mount inductors as a function of peak
current is shown in Figure 3. For applications where board
area is not a limiting factor, inductors with larger cores
can be used, which extends the recommended range of
Figure 3 to larger values.
For applications that have large input supply transients,
the OVLO pin can be used to disable switching above the
maximum operating voltage VIN(MAX) so that the minimum
inductor value is not artificially limited by a transient
condition. Inductor values that violate the above equation
10000
1000
100
10
100
1000
PEAK INDUCTOR CURRENT (mA)
7138 F03
Figure 3. Recommended Inductor Values for Maximum Efficiency
will cause the peak current to overshoot and permanent
damage to the part may occur.
Inductor Core Selection
Once the value for L is known, the type of inductor must
be selected. High efficiency regulators 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 satura-
tion. 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 materials are
small and do not radiate energy but generally cost more
than powdered iron core inductors with similar charac-
For more information www.linear.com/LTC7138
7138f
11
11 Page | ||
| Páginas | Total 24 Páginas | |
| PDF Descargar | [ Datasheet LTC7138.PDF ] | |
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