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PDF LT3493 Data sheet ( Hoja de datos )
| Número de pieza | LT3493 | |
| Descripción | 750kHz Step-Down Switching Regulator | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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FEATURES
n Wide Input Range: 3.6V to 36V Operating,
40V Maximum
n 1.2A Output Current
n Fixed Frequency Operation: 750kHz
n Output Adjustable Down to 780mV
n Short-Circuit Robust
n Uses Tiny Capacitors and Inductors
n Soft-Start
n Internally Compensated
n Low Shutdown Current: <2μA
n Low VCESAT Switch: 330mV at 1A
n Thermally Enhanced, Low Profile DFN Package
APPLICATIONS
n Automotive Battery Regulation
n Industrial Control Supplies
n Wall Transformer Regulation
n Distributed Supply Regulation
n Battery-Powered Equipment
LT3493
1.2A, 750kHz Step-Down
Switching Regulator in
2mm × 3mm DFN
DESCRIPTION
The LT®3493 is a current mode PWM step-down DC/DC
converter with an internal 1.75A power switch. The wide
operating input range of 3.6V to 36V (40V maximum)
makes the LT3493 ideal for regulating power from a wide
variety of sources, including unregulated wall transform-
ers, 24V industrial supplies and automotive batteries.
Its high operating frequency allows the use of tiny, low
cost inductors and ceramic capacitors, resulting in low,
predictable output ripple.
Cycle-by-cycle current limit provides protection against
shorted outputs and soft-start eliminates input current
surge during start-up. The low current (<2μA) shutdown
mode provides output disconnect, enabling easy power
management in battery-powered systems.
L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
wwwT.DYataPShIeCetA4UL.comAPPLICATION
VIN
4.2V TO 36V
ON OFF
3.3V Step-Down Converter
VIN BOOST
LT3493
SHDN
SW
GND FB
1μF
0.1μF 10μH
32.4k
10k
VOUT
3.3V
1.2A, VIN > 12V
0.95A, VIN > 5V
22pF
10μF
3493 TA01a
Efficiency
90
85
80
75
70
65
60
VIN = 12V
55 VOUT = 3.3V
L = 10μH
50
0 0.2 0.4 0.6 0.8
LOAD CURRENT (A)
1.0 1.2
3493 TA01b
3493fb
1
1 page  
LT3493
TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C unless otherwise noted.
SHDN Pin Current
50
45
40
35
30
25
20
15
10
5
0
0 2 4 6 8 10 12 14 16 18 20
VSHDN (V)
3493 G14
Typical Minimum Input Voltage
(VOUT = 5V)
7.5
TO START
7.0
6.5
6.0
TO RUN
5.5
5.0
1
10 100
IOUT (mA)
1000
3493 G15
Typical Minimum Input Voltage
(VOUT = 3.3V)
5.5
5.3
5.1
4.9
TO START
4.7
4.5
4.3
4.1
TO RUN
3.9
3.7
3.5
1
10 100
IOUT (mA)
1000
3493 G16
Switch Current Limit
2.0
1.9
1.8
1.7
1.6
1.5
1.4
1.3
1.2
1.1
1.0
www.DataSheet4U.com –50 –25 0 25 50 75 100 125 150
TEMPERATURE (°C)
3493 G17
Operating Waveforms
Switch Current Limit
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
0 20 40 60
DUTY CYCLE (%)
80 100
3493 G18
Operating Waveforms,
Discontinuous Mode
VSW
5V/DIV
IL
0.5A/DIV
0
VOUT
20mV/DIV
VIN = 12V
VOUT = 3.3V
IOUT = 0.5A
L = 10μH
COUT = 10μF
1μs/DIV
3493 G19
VSW
5V/DIV
IL
0.5A/DIV
0
VOUT
20mV/DIV
VIN = 12V
VOUT = 3.3V
IOUT = 50mA
L = 10μH
COUT = 10μF
1μs/DIV
3493 G20
3493fb
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5 Page 
APPLICATIONS INFORMATION
Table 2. Capacitor Vendors
VENDOR
PHONE
Panasonic
(714) 373-7366
Kemet
Sanyo
(864) 963-6300
(408) 749-9714
Murata
AVX
Taiyo Yuden
(404) 436-1300
(864) 963-6300
URL
www.panasonic.com
www.kemet.com
www.sanyovideo.com
www.murata.com
www.avxcorp.com
www.taiyo-yuden.com
PART SERIES COMMENTS
Ceramic,
Polymer,
Tantalum
EEF Series
Ceramic,
Tantalum
T494, T495
Ceramic,
Polymer,
Tantalum
POSCAP
Ceramic
Ceramic,
Tantalum
TPS Series
Ceramic
LT3493
capacitor must be large to achieve low ESR. Table 2 lists
several capacitor vendors.
Figure 4 shows the transient response of the LT3493 with
several output capacitor choices. The output is 3.3V. The
load current is stepped from 250mA to 1A and back to
250mA, and the oscilloscope traces show the output volt-
age. The upper photo shows the recommended value. The
second photo shows the improved response (less voltage
drop) resulting from a larger output capacitor and a phase
lead capacitor. The last photo shows the response to a high
performance electrolytic capacitor. Transient performance
is improved due to the large output capacitance.
www.DataSheet4U.com
BOOST Pin Considerations
Capacitor C3 and diode D2 are used to generate a boost
voltage that is higher than the input voltage. In most cases
a 0.1μF capacitor and fast switching diode (such as the
1N4148 or 1N914) will work well. Figure 5 shows two
ways to arrange the boost circuit. The BOOST pin must
be at least 2.3V above the SW pin for best efficiency. For
outputs of 3.3V and above, the standard circuit (Figure 5a)
is best. For outputs between 3V and 3.3V, use a 0.22μF
capacitor. For outputs between 2.5V and 3V, use a 0.47μF
capacitor and a small Schottky diode (such as the BAT-
54). For lower output voltages the boost diode can be tied
to the input (Figure 5b). The circuit in Figure 5a is more
efficient because the BOOST pin current comes from a lower
voltage source. You must also be sure that the maximum
voltage rating of the BOOST pin is not exceeded.
The minimum operating voltage of an LT3493 applica-
tion is limited by the undervoltage lockout (3.6V) and by
the maximum duty cycle as outlined above. For proper
start-up, the minimum input voltage is also limited by
the boost circuit. If the input voltage is ramped slowly,
or the LT3493 is turned on with its SHDN pin when the
output is already in regulation, then the boost capacitor
may not be fully charged. Because the boost capacitor is
charged with the energy stored in the inductor, the circuit
will rely on some minimum load current to get the boost
circuit running properly. This minimum load will depend
on the input and output voltages, and on the arrangement
of the boost circuit. The minimum load generally goes to
zero once the circuit has started. Figure 6 shows a plot of
minimum load to start and to run as a function of input
voltage. In many cases the discharged output capacitor
will present a load to the switcher which will allow it to
start. The plots show the worst-case situation where VIN
is ramping verly slowly. For lower start-up voltage, the
boost diode can be tied to VIN; however this restricts the
input range to one-half of the absolute maximum rating
of the BOOST pin.
3493fb
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11 Page | ||
| Páginas | Total 20 Páginas | |
| PDF Descargar | [ Datasheet LT3493.PDF ] | |
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