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參數(shù)資料
| 型號： | RT8803A |
| 廠商： | Richtek Technology Corporation |
| 英文描述： | 2/3-Phase PWM Controller for High-Density Power Supply |
| 中文描述： | 2/3-Phase PWM控制器的高密度電源 |
| 文件頁數(shù)： | 24/27頁 |
| 文件大小： | 553K |
| 代理商： | RT8803A |
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RT8803A
24
DS8803A-05 August 2007
www.richtek.com
All brandname or trademark belong to their owner respectively
Figure 8
Figure 10
Load Line without dead zone at light loads
1.31
1.23
1.24
1.25
1.26
1.27
1.28
1.29
1.3
0
5
10
15
20
25
I
OUT
(A)
V
C
R
CSN
open
R
CSN2
= 82k
w/o Dead Zone Compensation
w/i Dead Zone Compensation
Dead Zone Elimination
RT8803A samples and holds inductor current at 50%
period by time-sharing sourcing a current I
X
to R
CSN
. At
light load condition when inductor current is not balance,
voltage VCx
across the sensing capacitor would be
negative. It needs a negative I
X
to sense the voltage.
However, RT8803A CANNOT provide a negative I
X
and
consequently cannot sense negative inductor current. This
results in dead zone of load line performance as shown in
Figure 10. Therefore a technique as shown in Figure 11 is
required to eliminate the dead zone of load line at light
load condition.
Referring to Figure 11, I
X
is expressed as :
where I
LX_50%
is the of inductor current at 50% period. To
make sure RT8803A could sense the inductor current,
right hand side of Equation (1) should always be positive:
Since R
CSN
>> DCRx in practical application, Equation (2)
could be simplified as :
Figure 11. Application circuit o
f GM
(2)
(1)
CSN
LX_66%
I
CSN2
LX_66%
I
CSN2
OUT
V
X
R
DCRx
R
DCRx
R
I
×
+
×
+
=
0
R
DCRx
I
R
DCRx
I
R
V
CSN
LX_66%
CSN2
LX_66%
CSN2
OUT
≥
×
+
×
+
CSN
LX_66%
I
CSN2
OUT
V
R
DCRx
R
×
≥
R
CSN
GMx
Ix
+
-
R
CSN2
I
LX
Lx
DCRx
Rx
Cx
VCx
+
-
V
OUT
Figure 9
Current Balance Function
0
5
10
15
20
25
30
35
0
20
40
60
80
100
120
I
OUT
(A)
I
L
(
I
L1
I
L3
I
L2
Current Ratio Function
0
5
10
15
20
25
30
35
0
15
30
45
60
75
90
I
OUT
(A)
I
L
I
L3
I
L2
I
L1
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相關(guān)代理商/技術(shù)參數(shù) |
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|---|---|
| RT8803A_11 | 制造商:RICHTEK 制造商全稱:Richtek Technology Corporation 功能描述:2/3-Phase PWM Controller for High-Density Power Supply |
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