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PDF LTC3426 Data sheet ( Hoja de datos )
| Número de pieza | LTC3426 | |
| Descripción | 1.2MHz Step-Up DC/DC Converter | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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www.DataSheet4U.com
LTC3426
1.2MHz Step-Up DC/DC
Converter in SOT-23
FEATURES
■ Internal 2A MOSFET Switch
■ 1.2MHz Switching Frequency
■ Integrated Soft-Start
■ VIN Range: 1.6V to 4.3V
■ Low RDS(ON) Switch: 100mΩ at 5V Output
■ Delivers 5V at 800mA from a 3.3V Input
■ Delivers 3.3V at 800mA from a 2.5V Input
■ Uses Small, Low Profile External Components
■ Low Profile (1mm) SOT-23 (ThinSOTTM) Package
U
APPLICATIO S
■ White LED Driver Supply
■ Local 3.3V or 5V Supply
■ Battery Back-Up
TYPICAL APPLICATIO
3.3V to 5V Boost Converter
2.2µH
VIN
3.3V
10µF
SW
VIN VOUT
LTC3426
OFF ON
SHDN FB
GND
VOUT
5V
800mA
22µF
3426 TA01
DESCRIPTIO
The LTC®3426 step-up switching regulator generates an
output voltage of up to 5.5V from an input voltage as low
as 1.6V. Ideal for applications where space is limited, it
switches at 1.2MHz, allowing the use of tiny, low cost and
low profile external components. Its internal 2A, 100mΩ
NMOS switch provides high efficiency even at heavy load,
while the constant frequency, current mode architecture
results in low, predictable output noise that is easy to filter.
Antiringing circuitry reduces EMI concerns by damping
the inductor while in discontinuous mode, and internal
soft-start eases inrush current worries. Internal frequency
compensation is designed to accommodate ceramic out-
put capacitors, further reducing noise. The device features
very low shutdown current of 0.5µA.
The LTC3426 is available in the 6-lead SOT-23 package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
ThinSOT is a trademark of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
Protected by U.S. Patents, including 6498466, 6611131
Efficiency
100
VIN = 3.3V
95 VOUT = 5V
90
85
80
75
70
65
60
55
50
1 10 100
LOAD CURRENT (mA)
1000
3426 TA01b
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OPERATIO
The LTC3426 is a monolithic 1.2MHz boost converter
housed in a 6-lead SOT-23 package. The device features
fixed frequency, current mode PWM control for excellent
line and load regulation. The low RDS(ON) NMOS switch
enables the device to maintain high efficiency over a wide
range of load current. Operation of the feedback loop
which sets the peak inductor current to keep the output in
regulation can be best understood by referring to the Block
Diagram in Figure 1. At the start of each clock cycle a latch
in the PWM logic is set and the NMOS switch is turned on.
The sum of a voltage proportional to the switch current
and a slope compensating voltage ramp is fed to the
positive input to the PWM comparator. When this voltage
exceeds either a voltage proportional to the 2A current
limit or the PWM control voltage, the latch in the PWM
logic is reset and NMOS switch is turned off. The PWM
LTC3426
control voltage at the output of the error amplifier is the
amplified and compensated difference between the feed-
back voltage on the FB pin and the internal reference
voltage of 1.22V. If the control voltage increases, more
current is delivered to the output. When the control voltage
exceeds the ILIMIT reference voltage, the peak current is
limited to a minimum of 2A. The current limit helps protect
the LTC3426 internal switch and external components
connected to it. If the control voltage decreases, less
current is delivered to the output. During load transients
control voltage may decrease to the point where no
switching occurs until the feedback voltage drops below
the reference. The LTC3426 has an integrated soft-start
feature which slowly ramps up the feedback control node
from 0V. The soft-start is initiated when SHDN is pulled
high.
APPLICATIO S I FOR ATIO
Setting the Output Voltage
The output voltage, VOUT, is set by a resistive divider from
VOUT to ground. The divider tap is tied to the FB pin. VOUT
is set by the formula:
VOUT = 1.22 • ⎛⎝⎜1+ RR21⎞⎠⎟
Inductor Selection
The LTC3426 can utilize small surface mount inductors
due to its 1.2MHz switching frequency. A 1.5µH or 2.2µH
inductor will be the best choice for most LTC3426 appli-
cations. Larger values of inductance will allow greater
output current capability by reducing the inductor ripple
current. Increasing the inductance above 3.3µH will in-
crease component size while providing little improve-
ment in output current capability. The inductor current
ripple is typically set for 20% to 40% of the maximum
inductor current (IP). High frequency ferrite core inductor
materials reduce frequency dependent power losses com-
pared to cheaper powdered iron types, improving effi-
ciency. The inductor should have low DCR (DC resistance)
to reduce the I2R power losses, and must be able to
handle the peak inductor current without saturating.
Several inductor manufacturers are listed in Table 1.
Table 1. Inductor Manufacturers
TDK
Sumida
Murata
www.tdk.com
www.sumida.com
www.murata.com
Output and Input Capacitor Selection
Low ESR (equivalent series resistance) capacitors should
be used to minimize the output voltage ripple. Multilayer
ceramic capacitors are an excellent choice as they have
extremely low ESR and are available in small footprints. A
15µF to 30µF output capacitor is sufficient for most
applications. X5R and X7R dielectric materials are pre-
ferred for their ability to maintain capacitance over wide
voltage and temperature ranges.
Low ESR input capacitors reduce input switching noise
and reduce the peak current drawn from the input supply.
It follows that ceramic capacitors are also a good choice
for input decoupling and should be located as close as
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PACKAGE DESCRIPTIO
S6 Package
6-Lead Plastic TSOT-23
(Reference LTC DWG # 05-08-1636)
0.62 0.95
MAX REF
1.22 REF
2.90 BSC
(NOTE 4)
3.85 MAX 2.62 REF
1.4 MIN
2.80 BSC 1.50 – 1.75
(NOTE 4)
PIN ONE ID
LTC3426
RECOMMENDED SOLDER PAD LAYOUT
PER IPC CALCULATOR
0.20 BSC
DATUM ‘A’
0.95 BSC
0.80 – 0.90
1.00 MAX
0.30 – 0.50 REF
NOTE:
1. DIMENSIONS ARE IN MILLIMETERS
2. DRAWING NOT TO SCALE
3. DIMENSIONS ARE INCLUSIVE OF PLATING
0.09 – 0.20
(NOTE 3)
1.90 BSC
4. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR
5. MOLD FLASH SHALL NOT EXCEED 0.254mm
6. JEDEC PACKAGE REFERENCE IS MO-193
0.30 – 0.45
6 PLCS (NOTE 3)
0.01 – 0.10
S6 TSOT-23 0302
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
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| Páginas | Total 12 Páginas | |
| PDF Descargar | [ Datasheet LTC3426.PDF ] | |
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