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參數(shù)資料
| 型號(hào)： | RT8805 |
| 廠商： | Richtek Technology Corporation |
| 英文描述： | Two Phase General Purpose PWM Controller |
| 中文描述： | 兩相通用PWM控制器 |
| 文件頁(yè)數(shù)： | 11/15頁(yè) |
| 文件大?。?/td> | 387K |
| 代理商： | RT8805 |
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RT8805
Preliminary
11
DS8805-01 November 2005
www.richtek.com
Figure 8. Type 2 Bode Plot
10 100 1k 10k 100k 1M
Frequency (Hz)
-40
0
40
80
-60
80
40
0
20
60
-20
-40
-60
Loop Gain
Compensation
Gain
Modulator
Gain
G
There is another type of compensation called Type 3
compensation that adds a pole-zero pair to the Type 2
network. It's used to compensate output capacitor whose
ESR value is much lower (pure MLCC or OSCON
Capacitors).
As shown in Figure 9, to insert a network between V
OUT
and FB in the original Type 2 compensation network can
result in Type 3 compensation. Figure 10 shows the
difference of their AC response. Type 3 compensation has
an additional pole-zero pair that causes a gain boost at
the flat gain region. But the gain boosted is limited by the
ratio (R1+R4)/R4; if R3 << R4.
+
-
GM
V
COMP
C2
R2
C1
R4
V
OUT
R1
R3
C3
FB
Figure 9. Additional Network of Type 3 Compensation
(Add between V
OUT
and FB)
Figure 10. AC Response Curves of Type 2 and 3
Type 3 will induce three poles and two zeros.
Zeros :
C3
R3)
R1
(
2
1
+
F
C2
R2
2
1
F
Z2
Z1
×
×
=
×
×
=
π
π
;
R3
R1
C1
R3
+
R1
2
1
×
F
C3
R3
2
1
F
C2
C1
C2
C1
R2
2
1
F
P3
P2
P1
×
×
=
×
×
=
+
×
×
×
=
π
π
π
Poles :
which is in the origin.
We recommend F
Z1
placed in 0.5 x F
P(LC)
; F
Z2
placed in
F
P(LC)
; F
P1
placed in F
ESR
and F
P2
placed in 0.5 x F
SW
.
Figure 11 shows Type 3 Bode Plot.
Figure 11. Type 3 Bode Plot
Protection
OCP
The RT8805 uses
“
Cycle by Cycle
”
current comparison.
The over current level is set by IMAX pin. When OC
function occurs and SS > 3.7
V
, a constant current of 10
μ
A
starts to discharge the capacitor connected to SS pin
right away. When OC occurs, UGATE and LGATE will be
off.
Loop Gain
-80
-60
-40
-20
0
20
40
60
2
3
4
5
6
7
Log Frequency
d
Compensation Gain
Gain
Modulator Gain
Pole
F
P2
F
Z2
Add Type 3 compensation
Original Type 3 compensation
F
P1
F
Z1
F
P3
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相關(guān)代理商/技術(shù)參數(shù) |
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|---|---|
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