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PDF LTC3638 Data sheet ( Hoja de datos )
| Número de pieza | LTC3638 | |
| Descripción | 140V 250mA 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 20mA to 250mA 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
LTC3638
High Efficiency, 140V
250mA Step-Down
Regulator
DESCRIPTION
The LTC®3638 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 LTC3638 can supply up to 250mA 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 LTC3638’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 LTC3638 is a robust regulator
suited for regulating from a wide variety of power sources.
Additionally, the LTC3638 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 LTC3638s to be con-
nected in parallel for higher current applications.
The LTC3638 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, 250mA Step-Down Regulator
VIN
5V TO 140V
CIN
1µF
250V
VIN SW
LTC3638
RUN VFB
OVLO
SS
VPRG2 VPRG1
GND
L1
220µH
VOUT
5V
250mA
COUT
22µF
3638 TA01a
Efficiency and Power Loss vs Load Current
100
90 EFFICIENCY
80
70 VIN = 12V
60
VIN = 48V
VIN = 140V
1000
50
40 100
30
20 POWER LOSS 10
10
01
0.1 1 10 100 1000
LOAD CURRENT (mA)
3638 TA01b
For more information www.linear.com/LTC3638
3638fa
1
1 page  
TYPICAL PERFORMANCE CHARACTERISTICS
LTC3638
Quiescent Supply Current
vs Input Voltage
15
SLEEP
10
5
SHUTDOWN
0
0 30 60 90 120 150
VIN VOLTAGE (V)
3638 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)
3638 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
3638 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
3638 G12
Switch On-Resistance
vs Temperature
4 ISW = 250mA
3
2
1
Load Step Transient Response
OUTPUT
VOLTAGE
50mV/DIV
LOAD
CURRENT
100mA/DIV
VIN = 48V
200µs/DIV
VOUT = 3.3V
1mA TO 250mA LOAD STEP
FIGURE 15 CIRCUIT
3638 G15
0
–55 –25
5 35 65 95
TEMPERATURE (°C)
125 155
3638 G14
Operating Waveforms, VIN = 48V
OUTPUT
VOLTAGE
50mV/DIV
SWITCH
VOLTAGE
20V/DIV
INDUCTOR
CURRENT
500mA/DIV
VIN = 48V
10µs/DIV
VOUT = 3.3V
IOUT = 250mA
FIGURE 15 CIRCUIT
3638 G16
Operating Waveforms, VIN = 140V
OUTPUT
VOLTAGE
50mV/DIV
SWITCH
VOLTAGE
50V/DIV
INDUCTOR
CURRENT
500mA/DIV
VIN = 140V
10µs/DIV
VOUT = 3.3V
IOUT = 250mA
FIGURE 15 CIRCUIT
3638 G17
Short-Circuit and Recovery
OUTPUT
VOLTAGE
1V/DIV
INDUCTOR
CURRENT
500mA/DIV
500µs/DIV
FIGURE 15 CIRCUIT
3638 G18
For more information www.linear.com/LTC3638
3638fa
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5 Page 
LTC3638
APPLICATIONS INFORMATION
160 ISET OPEN
140
120 L = 47µH
100
80
L = 100µH
60
40 L = 220µH
20
0
0 30 60 90 120 150
VIN INPUT VOLTAGE (V)
3638 F03
Figure 3. Switching Frequency for VOUT = 3.3V
it is larger than a minimum value which can be computed
as follows:
L
>
VIN(MAX) • tON(MIN)
IPEAK
• 1.2
where VIN(MAX) is the maximum input supply voltage when
switching is enabled, tON(MIN) is 150ns, IPEAK is the peak
current, and the factor of 1.2 accounts for typical inductor
tolerance and variation over temperature.
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
will cause the peak current to overshoot and permanent
damage to the part may occur.
Although the previous equation provides the minimum
inductor value, higher efficiency is generally achieved with
a larger inductor value, which produces a lower switching
frequency. For a given inductor type, however, as induc-
tance is increased DC resistance (DCR) also increases.
Higher DCR translates into higher copper losses and lower
current rating, both of which place an upper limit on the
inductance. The recommended range of inductor values
for small surface mount inductors as a function of peak
current is shown in Figure 4. The values in this range are a
good compromise between the trade-offs discussed above.
10000
1000
100
10
10
100 1000
PEAK INDUCTOR CURRENT (mA)
3638 F04
Figure 4. Recommended Inductor Values for Maximum Efficiency
For applications 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 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-
teristics. The choice of which style inductor to use mainly
For more information www.linear.com/LTC3638
3638fa
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11 Page | ||
| Páginas | Total 26 Páginas | |
| PDF Descargar | [ Datasheet LTC3638.PDF ] | |
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