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| 型号： | LSP3105L18AD |
| 厂商： | LITE-ON SEMICONDUCTOR CORP |
| 元件分类： | 稳压器 |
| 英文描述： | SWITCHING REGULATOR, PDSO10 |
| 封装： | 3 X 3 MM, TDFN-10 |
| 文件页数： | 5/8页 |
| 文件大小： | 652K |
| 代理商： | LSP3105L18AD |
Liteon Semiconductor Corporation
LSP3105
2A Synchronous TDFN3*3-10L Step-Down Converter
Rev1.0
5/8
APPLICATION INFORMATION
INDUCTOR SELECTION
Under normal operation, the inductor maintains continuous current to the output. This inductor current has a ripple
that is dependent on the inductance value: higher inductance reduces the peak-to-peak ripple current. In general,
select an inductance value L based on ripple current requirement:
RIPPLE
OUTMAX
SW
IN
OUT
IN
OUT
K
I
f
V
)
V
(V
V
L
=
(1)
where VIN is the input voltage, VOUT is the output voltage, fSW is the switching frequency, IOUTMAX is the maximum
output current, and KRIPPLE is the ripple factor. Typically, choose KRIPPLE = 35% to correspond to the peak-to-peak
ripple current being 35% of the maximum output current.
With this inductor value (Table 1), the peak inductor current is IOUT (1 + KRIPPLE / 2). Make sure that this peak
inductor current is less than the 1.2A current limit. Finally, select the inductor core size so that it does not saturate at
the current limit value.
Table 1. Typical Inductor Values
VOUT
0.6V to 0.9V 0.9V to 1.8V
>1.8V
L
1.5H
2.2H
2.7H
INPUT CAPACITOR SELECTION
The input capacitor reduces input voltage ripple to the converter; a 4.7F ceramic capacitor is recommended for
most applications. The input capacitor should be placed as close as possible to IN and G, with short, wide traces.
OUTPUT CAPACITOR SELECTION
A low ESR output capacitor is required in order to maintain low output voltage ripple. Output ripple voltage is given
by:
ESR
RIPPLE
OUTMAX
RIPPLE
R
K
I
V
=
OUT
2
SW
IN
LC
f
28
V
+
(2)
where IOUTMAX is the maximum output current, KRIPPLE is the ripple factor, RESR is the ESR of the output capacitor, fSW
is the switching frequency, L is the inductor value, and COUT is the output capacitance. In the case of ceramic output
capacitors, RESR is very small and does not contribute to the ripple. Therefore, a lower capacitance value is
acceptable when ceramic capacitors are used. A 10F ceramic output capacitor is suitable for most applications.
OUTPUT VOLTAGE PROGRAMMING
Figure 3. Output Voltage Programming
Figure 3 shows the feedback network necessary to set the output voltage when the adjustable version is used.
Select the proper ratio of the two feedback resistors RFB1 and RFB2 based on the desired output voltage. Typically
choose RFB2 ≈ 100k and determine RFB1 from the output voltage:
=
1
0.6V
V
R
OUT
FB2
FB1
(3)
Connect a small capacitor across RFB1 for Feed forward capacitance at the FB pin:
FB1
ff
5/R
2E
C
=
(4)
where RFB1 = 600K, use 22pF. When using very low ESR output capacitors, such as ceramic, check for stability
while examining load-transient response, and increase the compensation capacitor C1 if needed.
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