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| 型号： | LSP3170SD |
| 厂商： | LITE-ON SEMICONDUCTOR CORP |
| 元件分类： | 稳压器 |
| 英文描述： | SWITCHING REGULATOR, PDSO8 |
| 封装： | SOP-8 |
| 文件页数： | 5/10页 |
| 文件大小： | 244K |
| 代理商： | LSP3170SD |
Liteon Semiconductor Corporation
LSP3170
2A Step Down DC/DC Converter
Rev1.5
4/10
APPLICATION INFORMATION
Output Voltage Setting
Figure1. Output Voltage Setting
Figure 1 shows the connections for setting the output voltage. Select the proper ratio of the two feedback resistors
RFB1 and RFB2 based on the output voltage. Typically, use RFB2 ≈ 10k and determine RFB1 from the following
equation:
(1)
Inductor Selection
The inductor maintains a continuous current to the output load. This inductor current has a ripple that is dependent
on the inductance value: higher inductance reduces the peak-to-peak ripple current. The trade off for high
inductance value is the increase in inductor core size and series resistance, and the reduction in current handling
capability. In general, select an inductance value L based on the ripple current requirement:
RIPPLE
OUTMAX
SW
IN
OUT
IN
OUT
K
I
f
V
)
V
(
V
L
=
(2)
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 = 30% to correspond to the peak-to-peak
ripple current being 30% of the maximum output current.
With this inductor value, the peak inductor current is IOUT (1 + KRIPPLE / 2). Make sure that this peak inductor current
is less that the 3A current limit. Finally, select the inductor core size so that it does not saturate at 3A. Typical
inductor values for various output voltages are shown in Table 1.
VOUT 1.5V 1.8V 2.5V 3.3V
5V
L
6.8H 6.8H 10H 15H 22H
Table 1. Typical Inductor Values
Input Capacitor
The input capacitor needs to be carefully selected to maintain sufficiently low ripple at the supply input of the
converter. A low ESR capacitor is highly recommended. Since large current flows in and out of this capacitor during
switching, its ESR also affects efficiency.
The input capacitance needs to be higher than 10F. The best choice is the ceramic type; however, low ESR
tantalum or electrolytic types may also be used provided that the RMS ripple current rating is higher than 50% of the
output current. The input capacitor should be placed close to the IN and G pins of the IC, with the shortest traces
possible. In the case of tantalum or electrolytic types, they can be further away if a small parallel 0.1F ceramic
capacitor is placed right next to the IC.
Output Capacitor
The output capacitor also needs to have low ESR to keep low output voltage ripple. The output ripple voltage is:
ESR
RIPPLE
OUTMAX
RIPPLE
R
K
I
V
=
OUT
2
SW
IN
LC
f
28
V
+
(3)
where IOUTMAX is the maximum output current, KRIPPLE is the ripple factor, RESR is the ESR of the output capacitor, fSW
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