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PDF LT3461A Data sheet ( Hoja de datos )
| Número de pieza | LT3461A | |
| Descripción | 1.3MHz/3MHz Step-Up DC/DC Converters with Integrated Schottky in ThinSOT | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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LT3461/LT3461A
1.3MHz/3MHz Step-Up
DC/DC Converters with
Integrated Schottky in ThinSOT
FEATURES
■ Integrated Schottky Rectifier
■ Fixed Frequency 1.3MHz/3MHz Operation
■ High Output Voltage: Up to 38V
■ Low VCESAT Switch: 260mV at 250mA
■ 12V at 70mA from 5V Input
■ 5V at 115mA from 3.3V Input
■ Wide Input Range: 2.5V to 16V
■ Uses Small Surface Mount Components
■ Low Shutdown Current: <1µA
■ Soft-Start
U■ Low Profile (1mm) SOT-23 (ThinSOTTM) Package
APPLICATIO S
■ Digital Cameras
■ CCD Bias Supply
■ XDSL Power Supply
■ TFT-LCD Bias Supply
■ Local 5V or 12V Supply
■ Medical Diagnostic Equipment
■ Battery Backup
DESCRIPTIO
The LT®3461/LT3461A are general purpose fixed fre-
quency current mode step-up DC/DC converters. Both
devices feature an integrated Schottky and a low VCESAT
switch allowing a small converter footprint and lower parts
cost. The LT3461 switches at 1.3MHz while the LT3461A
switches at 3MHz. These high switching frequencies en-
able the use of tiny, low cost and low height capacitors and
inductors. The constant switching frequency results in
predictable output noise that is easy to filter, and the
inductor based topology ensures an input free from switch-
ing noise typically present with charge pump solutions.
The high voltage switch in the LT3461/LT3461A is rated at
40V making the device ideal for boost converters up to
38V.
The LT3461/LT3461A are available in a low profile (1mm)
SOT-23 package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
ThinSOT is a trademark of Linear Technology Corporation.
TYPICAL APPLICATIO
5V to 12V, 70mA Step-Up DC/DC Converter
L1
VIN 10µH
5V 1
C1
1µF
OFF ON
6 SW
5
VIN VOUT
LT3461A
43
SHDN FB
GND
2
261k
30.1k
VOUT
12V
70mA
15pF
C2
1µF
3461 TA01a
Efficiency
85
80
VIN = 5V
75 VIN = 3.3V
70
65
60
0
20 40 60
LOAD CURRENT (mA)
80
3461 TAO1b
3461af
1
1 page  
LT3461/LT3461A
APPLICATIO S I FOR ATIO
Inrush Current
The LT3461 has a built-in Schottky diode. When supply
voltage is applied to the VIN pin, the voltage difference
between VIN and VOUT generates inrush current flowing
from input through the inductor and the Schottky diode to
charge the output capacitor. The maximum nonrepetitive
surge current the Schottky diode in the LT3461 can
sustain is 1.5A. The selection of inductor and capacitor
value should ensure the peak of the inrush current to be
below 1.5A. In addition, turn-on of the LT3461 should be
delayed until the inrush current is less than the maximum
current limit. The peak inrush current can be calculated as
follows:
⎛⎞
IP
=
VIN –
L
C
0.6
–1
• exp
⎜
⎜−
⎜
⎝⎜
2
π
⎟
⎟
L
C
⎟
− 1⎠⎟
where L is the inductance, r is the resistance of the
inductor and C is the output capacitance.
Table 3 gives inrush peak currents for some component
selections.
Table 3. Inrush Peak Current
VIN (V)
5
L (µH)
4.7
5 10
C (µF)
1
1
IP (A)
1.1
0.9
Thermal Considerations
Significant power dissipation can occur on the LT3461
and LT3461A, particularly at high input voltage. Device
load, voltage drops in the power path components, and
switching losses are the major contributors. It is impor-
tant to measure device power dissipation in an application
to ensure that the LT3461 does not exceed the absolute
maximum operating junction temperature of 125°C over
the operating ambient temperature range. Generally, for
supply voltages below 5V the integrated current limit
function provides adequate protection for nonfault condi-
tions. For supply voltages above 5V, Figures 3a and 3b
show the recommended operating region of the LT3461
and LT3461A, respectively. These graphs are based
on 250mW on-chip dissipation. Improvement of these
numbers can be expected if the LT3461 is supplied from a
separate low voltage rail.
160
VIN = 5V
VIN = 8V
120 VIN = 12V
VIN >15V
80
40
0
6 14 22 30 38
VOUT (V)
3461 F01a
Figure 3a. LT3461 Operating Region
160
VIN = 5V
120 VIN = 8V
VIN = 12V
VIN >15V
80
40
0
6 14 22 30 38
VOUT (V)
3461 F01b
Figure 3b. LT3461A Operating Region
Switching Frequency
The key difference between the LT3461 and LT3461A is the
faster switching frequency of the LT3461A. At 3MHz, the
LT3461A switches at twice the rate of the LT3461. The
higher switching frequency of the LT3461A allows physi-
cally smaller inductors and capacitors to be used in a given
application, but with a slight decrease in efficiency and
maximum output current when compared to the LT3461.
Generally if efficiency and maximum output current are
crucial, or a high output voltage is being generated, the
LT3461 should be used. If application size and cost are
more important, the LT3461A will be the better choice.
3461af
5
5 Page | ||
| Páginas | Total 8 Páginas | |
| PDF Descargar | [ Datasheet LT3461A.PDF ] | |
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