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PDF LSP3105 Data sheet ( Hoja de datos )
| Número de pieza | LSP3105 | |
| Descripción | 2A Synchronous Step-Down Converter | |
| Fabricantes | Lite-On | |
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Liteon Semiconductor Corporation
LSP3105
2A Synchronous TDFN3*3-10L Step-Down Converter
FEATURES
High Efficiency - Up to 95%
Low 300µA Quiescent Current
Guaranteed 2A Output Current
1.2MHz Constant Frequency Operation
Internal Synchronous Rectifier Eliminates Schottky
Diode
2.5V to 6V input voltage range
Adjustable Output Voltages From 0.6V to VIN
Fixed Output Voltage Options Available
100% Duty Cycle Low-Dropout Operation
<1µA Shutdown Current
Soft start function
Short circuit protection
Thermal shutdown protection
TDFN3*3-10L Package
GENERAL DESCRIPTION
The LSP3105 is a fixed-frequency current-mode
synchronous PWM step down converter that is capable
of delivering 2A of output current while achieving peak
efficiency of 95%.LSP3105 operates in a 100% Duty
Cycle Low-Dropout Operation, maximizing battery life in
portable applications. The LSP3105 operates with a
fixed frequency of 1.2MHz, allowing the use of small
external components. The LSP3105 is an ideal solution
for applications powered by Li-Ion batteries or other
portable applications that require small board space.
The LSP3105 is available in 1.8V fixed output voltage
and an adjustable output voltage version capable of
generating output voltages from 0.6V to VIN .The
LSP3105 is available in the small TDFN3*3-10L
package.
APPLICATIONS
Microprocessor and DSP core power supplies
Cellular and smart Phones
Wireless and DSL Modems
Portable Instruments
Figure1. Typical Application Circuit and Efficiency
1/8 Rev1.0
Free Datasheet http://www.datasheet4u.com/
1 page  
Liteon Semiconductor Corporation
LSP3105
2A Synchronous TDFN3*3-10L Step-Down Converter
APPLICATION INFORMATION
INDUCTOR SELECTION
Under normal operation, the inductor maintains continuous current to the output. This inductor current has a ripple
that is dependent on the inductance value: higher inductance reduces the peak-to-peak ripple current. In general,
select an inductance value L based on ripple current requirement:
L = VOUT • (VIN − VOUT )
V f I KIN SW OUTMAX RIPPLE
(1)
where VIN is the input voltage, VOUT is the output voltage, fSW is the switching frequency, IOUTMAX is the maximum
output current, and KRIPPLE is the ripple factor. Typically, choose KRIPPLE = 35% to correspond to the peak-to-peak
ripple current being 35% of the maximum output current.
With this inductor value (Table 1), the peak inductor current is IOUT • (1 + KRIPPLE / 2). Make sure that this peak
inductor current is less than the 1.2A current limit. Finally, select the inductor core size so that it does not saturate at
the current limit value.
Table 1. Typical Inductor Values
VOUT 0.6V to 0.9V 0.9V to 1.8V
L 1.5µH
2.2µH
>1.8V
2.7µH
INPUT CAPACITOR SELECTION
The input capacitor reduces input voltage ripple to the converter; a 4.7µF ceramic capacitor is recommended for
most applications. The input capacitor should be placed as close as possible to IN and G, with short, wide traces.
OUTPUT CAPACITOR SELECTION
A low ESR output capacitor is required in order to maintain low output voltage ripple. Output ripple voltage is given
by:
VRIPPLE
= IOUTMAX K RIPPLE RESR
+ VIN
28 • f SW 2 LCOUT
(2)
where IOUTMAX is the maximum output current, KRIPPLE is the ripple factor, RESR is the ESR of the output capacitor, fSW
is the switching frequency, L is the inductor value, and COUT is the output capacitance. In the case of ceramic output
capacitors, RESR is very small and does not contribute to the ripple. Therefore, a lower capacitance value is
acceptable when ceramic capacitors are used. A 10µF ceramic output capacitor is suitable for most applications.
OUTPUT VOLTAGE PROGRAMMING
Figure 3. Output Voltage Programming
Figure 3 shows the feedback network necessary to set the output voltage when the adjustable version is used.
Select the proper ratio of the two feedback resistors RFB1 and RFB2 based on the desired output voltage. Typically
choose RFB2 ≈ 100kΩ and determine RFB1 from the output voltage:
RFB1
=
RFB2
⎜⎛
⎝
VOUT
0.6V
− 1⎟⎞
⎠
(3)
Connect a small capacitor across RFB1 for Feed forward capacitance at the FB pin:
Cff = 2E − 5/R FB1
(4)
where RFB1 = 600KΩ, use 22pF. When using very low ESR output capacitors, such as ceramic, check for stability
while examining load-transient response, and increase the compensation capacitor C1 if needed.
5/8 Rev1.0
Free Datasheet http://www.datasheet4u.com/
5 Page | ||
| Páginas | Total 8 Páginas | |
| PDF Descargar | [ Datasheet LSP3105.PDF ] | |
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