LX1910CDU MICROSEMI [Microsemi Corporation], LX1910CDU Datasheet - Page 5

• Manufacturer Part Number: LX1910CDU
• Description: Step-Down Regulator
• Manufacturer: MICROSEMI [Microsemi Corporation]

Copyright © 2004
Rev. 1.1, 2005-02-25
O
F
that improves power management efficiency across the
output load range.
optional capacitor C
the transient response (see Figure 1). The value of R2
should be less than 100KΩ.
determined using the following equation, note V
referred to as V
D
LX1910 because it provides fast switching and superior
reverse recovery performance. The
(20V @ 1A) makes an effective choice for most
applications.
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.
values and choosing a value between 2.2µH and 30µH
supports a majority of applications.
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.
D
I
NDUCTOR
UNCTIONAL
UTPUT
ESIGN
IODE
Resistors R1 and R2 program the output voltage. An
A Schottky diode is recommended for use with the
Selecting the appropriate inductor type and value ensures
The LX1910 allows for a broad selection of inductor
The LX1910 implements a PFM / PWM architecture
Let R2 equal 50K and the required V
R1
R1
TM
S
E
=
=
V
ELECTION
XAMPLE
50K
R2
OLTAGE
S
ELECTION
⎡
⎢
⎢
⎣
D
⎛
⎜
⎜
⎝
⎡
⎢
⎢
⎣
⎛
⎜ ⎜
⎝
FBT
V
V
1.17
ESCRIPTION
3V
OUT
REF
:
.
⎞
⎟ ⎟
⎠
P
−
X
⎞
⎟
⎟
⎠
ROGRAMMING
1
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: [phone]
may be inserted across R1 to improve
−
⎤
⎥
⎥
⎦
1
=
⎤
⎥
⎥
⎦
78KΩ
The value of R1 can be
Microsemi
Selecting a larger
OUT
equal to 3.0V.
A P P L I C A T I O N N O T E
Integrated Products Division
REF
UPS5817
®
Microsemi
is also
series resistance (ESR) are recommended.
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.
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.
sufficient size to effectively decouple the input voltage
source impedance (e.g., C
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
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
reduce high frequency noise and decoupling the V
using a 0.1µF capacitor.
C
L
AYOUT
APACITOR
To minimize ripple voltage, output capacitors with a low
The high peak currents and switching frequencies present
C
ONSIDERATIONS
S
Step-Down Regulator
P
ELECTION
RODUCTION
Finally, choose an input capacitor of
IN
> 4.7µF).
D
ATA
OUT
S
HEET
IN
, C
pin and GND pin to
OUT
Other low ESR
, the Schottky
Multi-layer
LX1910
IN
pin
Page 5