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參數(shù)資料
| 型號： | LSP3170SD |
| 廠商： | LITE-ON SEMICONDUCTOR CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | SWITCHING REGULATOR, PDSO8 |
| 封裝： | SOP-8 |
| 文件頁數(shù)： | 6/10頁 |
| 文件大小： | 244K |
| 代理商： | LSP3170SD |
Liteon Semiconductor Corporation
LSP3170
2A Step Down DC/DC Converter
Rev1.5
5/10
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 can be
used for ceramic capacitors. In the case of tantalum or electrolytic capacitors, the ripple is dominated by RESR
multiplied by the ripple current. In that case, the output capacitor is chosen to have sufficiently low ESR.
For ceramic output capacitors, typically choose a capacitance of about 22F. For tantalum or electrolytic capacitors,
choose a capacitor with less than 50m ESR.
Rectifier Diode
Use a Schottky diode as the rectifier to conduct current when the High-Side Power Switch is off. The Schottky diode
must have a current rating higher than the maximum output current and a reverse voltage rating higher than the
maximum input voltage.
Stability Compensation
CCOMP2 is needed only for high ESR output capacitor
Figure 2. Stability Compensation
The feedback loop of the IC is stabilized by the components at the COMP pin, as shown in Figure 2. The DC loop
gain of the system is determined by the following equation:
(4)
The dominant pole P1 is due to CCOMP:
COMP
VEA
EA
1
P
C
A
π
2
G
f
=
(5)
The second pole P2 is the output pole:
OUT
2
P
C
V
π
2
I
f
=
(6)
The first zero Z1 is due to RCOMP and CCOMP:
COMP
1
Z
C
R
π
2
1
f
=
(7)
And finally, the third pole is due to RCOMP and CCOMP2 (if CCOMP2 is used):
2
COMP
3
P
C
R
π
2
1
f
=
(8)
The following steps should be used to compensate the IC:
STEP1. Set the crossover frequency at 1/10 of the switching frequency via RCOMP:
(9)
but limit RCOMP to 10k maximum.
STEP2. Set the zero fZ1 at 1/4 of the crossover frequency. If RCOMP is less than 10k, the equation for CCOMP is:
)
F
(
R
10
8
.
1
C
COMP
5
COMP
×
=
(10)
If RCOMP is limited to 10k, then the actual crossover frequency is 10/ (VOUTCOUT). Therefore:
)
F
(
C
V
10
2
.
1
C
OUT
5
COMP
×
=
(11)
STEP3. If the output capacitor’s ESR is high enough to cause a zero at lower than 4 times the crossover frequency,
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