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參數(shù)資料
| 型號： | LX1910-CDUT |
| 廠商： | MICROSEMI CORP-ANALOG MIXED SIGNAL GROUP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | 0.8 A SWITCHING REGULATOR, 1325 kHz SWITCHING FREQ-MAX, PDSO8 |
| 封裝： | PLASTIC, MSOP-8 |
| 文件頁數(shù)： | 11/12頁 |
| 文件大小： | 602K |
| 代理商： | LX1910-CDUT |
LX1910
PRELIMINARY DATA SHEET
Microsemi
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 8
WWW
.Microse
m
i
.CO
M
High Frequency Step Down Regulator
I N T E GR A T ED
PRODUCT S
Copyright
2000
Rev. 0.9a, 2004-04-16
APPLICATION NOTE
O
F
TH
C
L
2
1
4
C
R
2
1
π
=
π
Solving for the Feed-Forward capacitor (CF) yields.
TH
O
F
R
4
C
L
C
=
eq. 12
It is generally good practice to roll off the upper frequency
response to prevent any high gain of high frequency noise.
This pole is setup by the RF/CF combination.
The
frequency of this pole should be set high enough so as to
not counteract the influence of the zeros.
Setting the
frequency of the pole to ten times the frequency of ZF2
yields the following equation:
2
Z
2
P
F
10
F
=
yielding
F
TH
F
C
R
2
10
C
R
2
1
π
=
π
Solving for the Feed-forward resistor (RF) yields.
10
R
TH
F =
eq. 13
The calculated zeros will yield approximately 50
° to 90°
of phase margin regardless of the type of output capacitors
resulting in an unconditionally stable circuit design. Using
the previous equations, both phase margin and close-loop
bandwidth are optimized.
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. Minimize trace capacitance by reducing the etch
area connecting the SW pin to the inductor
4. Minimizing the etch length to the FB pin to reduce
noise coupling into this high impedance sense input.
Other considerations optionally include placing a 0.1F
capacitor between the LX1910 VOUT pin and GND pin to
reduce high frequency noise and decoupling the VIN pin
using a 0.1F capacitor.
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.
DESIGN EXAMPLE
Given the following application requirements:
=
m
5
.
1
ESR
MHz
1
f
mV
5
V
mA
600
I
V
5
.
2
V
3
.
3
to
V
5
.
5
V
OSC
)
MAX
(
RIPPLE
)
MAX
(
OUT
IN
Inductor Calculation:
Calculate the required circuit components. First calculate
the output inductor based on the maximum desired
inductor ripple current using eq. 2. Since the inductor
ripple is largest at higher input voltages, use the maximum
VIN specified.
()
H
.7
4
H
38
.
3
L
V
5
.
5
V
5
.
2
1
mA
120
MHz
1
L
V
1
%
20
I
f
1
L
IN
OUT
DC
OSC
=
=
=
Output Capacitor Calculation:
Next the output capacitance can be calculated based on the
maximum desired ripple voltage using eq. 3.
+
=
+
=
OUT
OSC
RIPPLE
C
MHz
1
8
1
m
5
.
1
mA
120
mV
5
C
f
8
1
ESR
I
V
Solving for COUT yields:
AA
PP
LL
IICC
AA
TT
IIOO
NN
SS
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