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參數(shù)資料
| 型號： | LX1910 |
| 廠商： | Microsemi Corporation |
| 英文描述： | Step-Down Regulator |
| 中文描述： | 降壓穩(wěn)壓器 |
| 文件頁數(shù)： | 5/8頁 |
| 文件大?。?/td> | 239K |
| 代理商： | LX1910 |
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
W
M
.
C
LX1910
Step-Down Regulator
P
RODUCTION
D
ATA
S
HEET
TM
A P P L I C A T I O N N O T E
F
UNCTIONAL
D
ESCRIPTION
The LX1910 implements a PFM / PWM architecture
that improves power management efficiency across the
output load range.
O
UTPUT
V
OLTAGE
P
ROGRAMMING
Resistors R1 and R2 program the output voltage. An
optional capacitor C
X
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 V
REF
is also
referred to as V
FBT
.
V
R2
R1
REF
1
V
OUT
=
D
ESIGN
E
XAMPLE
:
Let R2 equal 50K and the required V
OUT
equal to 3.0V.
78K
=
1
50K
R1
1.17
3V
=
D
IODE
S
ELECTION
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.
I
NDUCTOR
S
ELECTION
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.
C
APACITOR
S
ELECTION
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., C
IN
> 4.7μF).
L
AYOUT
C
ONSIDERATIONS
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 C
IN
, C
OUT
, 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 V
OUT
pin and GND pin to
reduce high frequency noise and decoupling the V
IN
pin
using a 0.1μF capacitor.
A
P
P
L
I
C
A
T
I
O
N
S
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