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PDF LX1910 Data sheet ( Hoja de datos )
| Número de pieza | LX1910 | |
| Descripción | Step-Down Regulator | |
| Fabricantes | Microsemi Corporation | |
| Logotipo |  |
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LX1910
TM ® Step-Down Regulator
PRODUCTION DATA SHEET
DESCRIPTION
The LX1910 PWM buck regulator
achieves very high efficiencies over a
broad range of operating load
conditions. The LX1910 implements
a load-detection architecture and
enters a power-saving PFM mode
when driving small load currents
ensuring optimal regulator efficiency
over the entire output current range
thus maximizing battery life.
The LX1910 does not require a
minimum load current for stable
operation. There is no Under Voltage
Lockout for the input voltage,
operational range includes 4V to 6V.
The regulator is capable of providing
an output dc load current of 850mA.
The SHDN pin places the device in a
sleep-mode drawing less than 1µA of
quiescent current.
The PWM operating mode
implements a fixed frequency of
1MHz (typ), the transconductance
error amplifier has 12µA of drive
with an output voltage swing rail to
rail. Compensation is external for
maximum user flexibility.
The LX1910 comes in space-saving
MSOP package allowing a complete
application circuit to occupy a very
small PCB area. These features make
the LX1910 ideal for use in
SmartPhones, PDAs, or other battery-
operated devices
IMPORTANT: For the most current data, consult MICROSEMI’s website: http://www.microsemi.com
KEY FEATURES
Internal Reference 1.17V
±2% Accuracy (Line and
Temperature)
4V to 6.0V Input Range
Adj. Output From 1.17V to VIN
Output Current (IDC >850mA)
Quiescent Current < 300µA
1MHz Operation Frequency
MSOP 8-Pin
APPLICATIONS/BENEFITS
Portable Microprocessor Core
Voltage Supplies
5V to 3V
VIN
CIN
RC
CC
PRODUCT HIGHLIGHT
LX1910
PVIN
AVIN
SHDN
COMP
AGND
SW
FB
PGND
D
L
CX R1
R2
VOUT
COUT
90%
80%
70%
60%
50%
40%
30%
LX1910 Efficiency @ Vout=1.5V
20%
10%
0
100 200 300 400 500 600
OUTPUT CURRENT, mA
Figure 1 – LX1910 Circuit Topology and Typical Efficiency Performance
700
PACKAGE ORDER INFO
TJ(°C)
Input
Voltage
Output
Voltage Range
Plastic MSOP
DU 8-PIN
RoHS Compliant / Pb-free
0 to 85
4.5V – 6.0V 1.17V to VIN
LX1910CDU
Note: Available in Tape & Reel. Append the letters “TR” to the part number.
(i.e. LX1910-13016CDU-TR)
Copyright © 2004
Rev. 1.1, 2005-02-25
DataSheet4 U .com
Microsemi
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 1
1 page  
www.DataSheet4U.com
LX1910
TM ® Step-Down Regulator
PRODUCTION DATA SHEET
APPLICATION NOTE
FUNCTIONAL DESCRIPTION
The LX1910 implements a PFM / PWM architecture
that improves power management efficiency across the
output load range.
OUTPUT VOLTAGE PROGRAMMING
Resistors R1 and R2 program the output voltage. An
optional capacitor CX may be inserted across R1 to improve
the transient response (see Figure 1). The value of R2
should be less than 100KΩ. The value of R1 can be
determined using the following equation, note VREF is also
referred to as VFBT.
R1 =
R2⎢⎢⎣⎡⎜⎜⎝⎛
VOUT
VREF
⎟⎟⎠⎞
⎤
− 1⎥
⎥⎦
DESIGN EXAMPLE:
Let R2 equal 50K and the required VOUT equal to 3.0V.
R1
=
50K ⎢⎢⎣⎡⎜⎜⎝⎛
3V
1.17
⎟⎟⎠⎞
−1⎥⎤
⎥⎦
= 78KΩ
DIODE SELECTION
A Schottky diode is recommended for use with the
LX1910 because it provides fast switching and superior
reverse recovery performance. The Microsemi UPS5817
(20V @ 1A) makes an effective choice for most
applications.
INDUCTOR SELECTION
Selecting the appropriate inductor type and value ensures
optimal performance of the converter circuit for the
intended application. This selection process requires the
designer to make trade-offs between circuit performance
and cost. A primary consideration requires the selection of
an inductor that will not saturate at the peak current level.
Other considerations that affect inductor choice include
EMI, output voltage ripple, and overall circuit efficiency.
The inductor that works best depends upon the application’s
requirements. Further, some experimentation with actual
devices in-circuit is typically necessary to make the most
effective choice.
The LX1910 allows for a broad selection of inductor
values and choosing a value between 2.2µH and 30µH
supports a majority of applications. Selecting a larger
inductor value can increase efficiency and reduce output
voltage ripple. Smaller inductors typically provide smaller
package size (critical in many portable applications) at the
expense of increasing output ripple current. Regardless of
inductor value, selecting a device manufactured with a
ferrite-core produces lower losses at higher switching
frequencies and thus better overall performance.
CAPACITOR SELECTION
To minimize ripple voltage, output capacitors with a low
series resistance (ESR) are recommended. Multi-layer
ceramic capacitors with X5R or X7R dielectric make an
effective choice because they feature small size, very low
ESR, a temperature stable dielectric, and can be connected in
parallel to increase capacitance. Typical capacitance values
of 4.7 to 30µF have proven effective. Other low ESR
capacitors such as solid tantalum, specialty polymer, or
organic semiconductor, make effective choices provided that
the capacitor is properly rated for the output voltage and
ripple current. Finally, choose an input capacitor of
sufficient size to effectively decouple the input voltage
source impedance (e.g., CIN > 4.7µF).
LAYOUT CONSIDERATIONS
The high peak currents and switching frequencies present
in DC/DC converter applications require careful attention to
device layout for optimal performance. Basic design rules
include: (1) maintaining wide traces for power components
(e.g., width > 50mils); (2) place CIN, COUT, the Schottky
diode, and the inductor close to the LX1910; (3) minimizing
trace capacitance by reducing the etch area connecting the
SW pin to the inductor; and (4) minimizing the etch length to
the FB pin to reduce noise coupling into this high impedance
sense input. Other considerations include placing a 0.1uF
capacitor between the LX1910 VOUT pin and GND pin to
reduce high frequency noise and decoupling the VIN pin
using a 0.1µF capacitor.
Copyright © 2004
Rev. 1.1, 2005-02-25
DataSheet4 U .com
Microsemi
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 5
5 Page | ||
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| PDF Descargar | [ Datasheet LX1910.PDF ] | |
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