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參數(shù)資料
| 型號： | LX1910-CDU |
| 廠商： | MICROSEMI CORP-ANALOG MIXED SIGNAL GROUP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | 1 A SWITCHING REGULATOR, 1200 kHz SWITCHING FREQ-MAX, PDSO8 |
| 封裝： | LEAD FREE, PLASTIC, MSOP-8 |
| 文件頁數(shù)： | 5/8頁 |
| 文件大?。?/td> | 239K |
| 代理商： | LX1910-CDU |
Microsemi
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 5
Copyright
2004
Rev. 1.1, 2005-02-25
WWW
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LX1910
Step-Down Regulator
PRODUCTION DATA SHEET
TM
APPLI CATI ON 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 100K. The value of R1 can be
determined using the following equation, note VREF is also
referred to as VFBT.
1
V
R2
R1
REF
OUT
=
DESIGN EXAMPLE:
Let R2 equal 50K and the required VOUT equal to 3.0V.
78K
1
50K
R1
1.17
3V
=
=
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 2.2H and 30H
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 30F 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 > 4.7F).
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 0.1F capacitor.
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