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參數(shù)資料
| 型號： | RT9209 |
| 英文描述： | Step-down DC/DC Converter |
| 中文描述： | 降壓直流/直流轉(zhuǎn)換器 |
| 文件頁數(shù)： | 11/16頁 |
| 文件大?。?/td> | 315K |
| 代理商： | RT9209 |
Preliminary
RT9203/A
DS9203/A-04 May 2003
www.richtek.com
11
Fig. 5
Applications Information
Inductor Selection
The RT9203/A was designed for V
IN
= 5V, step-down
application mainly. Fig.6 shows the typical topology
and waveforms of step-down converter.
The ripple current of inductor can be calculated as
follows:
IL
RIPPLE
= (5V - V
OUT
)/L
×
T
ON
Because operation frequency is fixed at 300kHz,
T
ON
= 3.33
×
V
OUT
/5V
The V
OUT
ripple is
V
OUT RIPPLE
= IL
RIPPLE
×
ESR
ESR is the equivalent series resistor of output
capacitor
Table 1 shows the ripple voltage of V
OUT
at
V
IN
= 5V
Table 1
Fig. 6
V
OUT
3.3V
2.5V
1.5V
Inductor
1000
μ
F (ESR=53m
)
1500
μ
F (ESR=33m
)
3000
μ
F (ESR=21m
)
*Refer to Sanyo low ESR series (CE, DX, PX…)
The suggested L and C are as follows:
2
μ
H with
≥
1500
μ
F C
OUT
5
μ
H with
≥
1000
μ
F C
OUT
2
μ
H
100mV
62mV
40mV
5
μ
H
40mV
25mV
16mV
2
μ
H
110mV
68mV
43mV
5
μ
H
44mV
28mV
18mV
2
μ
H
93mV
58mV
37mV
5
μ
H
37mV
23mV
15mV
T
ON
T
OFF
T
S
V
L
V
I
-
V
O
-
V
O
I
L
= I
O
i
L
μ
Q
μ
I
L
i
Q
I
Q
i
D
I
D
C.C.M.
V
L
R
V
O
L
D
C
Q
V
I
0A
0V
2V
4V
I
S
I
T0T1
T2
T3
TIME
COUNT = 1
COUNT = 2
COUNT = 3
OVERLOAD
APPLIED
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