參數(shù)資料
型號(hào): IRU3138
廠商: International Rectifier
英文描述: SYNCHRONOUS PWM CONTROLLER FOR TERMINATION POWER SUPPLY APPLICATIONS
中文描述: 同步PWM控制器終止電源應(yīng)用
文件頁數(shù): 11/18頁
文件大?。?/td> 281K
代理商: IRU3138
IRU3138
11
Rev. 1.0
01/29/04
www.irf.com
For a general solution for unconditionally stability for
ceramic capacitor with very low ESR and any type of
output capacitors, in a wide range of ESR values we
should implement local feedback with a compensation
network. The typically used compensation network for
voltage-mode controller is shown in Figure 10.
Figure 10 - Compensation network with local
feedback and its asymptotic gain plot.
In such configuration, the transfer function is given by:
The error amplifier gain is independent of the transcon-
ductance under the following condition:
By replacing Z
IN
and Z
f
according to Figure 7, the trans-
former function can be expressed as:
As known, transconductance amplifier has high imped-
ance (current source) output, therefore, consider should
be taken when loading the E/A output. It may exceed its
source/sink output current capability, so that the ampli-
fier will not be able to swing its output voltage over the
necessary range.
The compensation network has three poles and two ze-
ros and they are expressed as follows:
Cross Over Frequency:
The stability requirement will be satisfied by placing the
poles and zeros of the compensation network according
to following design rules. The consideration has been
taken to satisfy condition (20) regarding transconduc-
tance error amplifier.
These design rules will give a crossover frequency ap-
proximately one-tenth of the switching frequency. The
higher the band width, the potentially faster the load tran-
sient speed. The gain margin will be large enough to
provide high DC-regulation accuracy (typically -5dB to -
12dB). The phase margin should be greater than 45
8
for
overall stability.
Based on the frequency of the zero generated by ESR
versus crossover frequency, the compensation type can
be different. The table below shows the compensation
type and location of crossover frequency.
V
OUT
Vp=V
REF
R
5
R
6
R
8
C
10
C
12
C
11
R
7
Ve
F
Z
1
F
Z
2
F
P
2
F
P
3
E/A
Z
f
Z
IN
Frequency
Gain(dB)
H(s) dB
Fb
Comp
H(s) =
1+sR
7
C
12
+C
11
×
(1+sR
8
C
10
)
(1+sR
7
C
11
)
×
[1+sC
10
(R
6
+R
8
)]
×
[ ( )]
1
sR
6
(C
12
+C
11
)
C
12
C
11
g
m
Z
f
>> 1 and g
m
Z
IN
>>1 ---(20)
1 - g
m
Z
f
1 + g
m
Z
IN
V
e
V
OUT
=
Where:
V
IN
= Maximum Input Voltage
V
OSC
= Oscillator Ramp Voltage
Lo = Output Inductor
Co = Total Output Capacitors
F
O
= R
7
×
C
10
×
×
V
IN
V
OSC
1
2
π×
Lo
×
Co
---(21)
F
P1
= 0
1
π×
C
10
×
(R
6
+ R
8
)
F
Z2
= 2
1
2
π×
C
10
×
R
6
F
Z1
=
1
2
π×
R
7
×
C
11
F
P3
=
2
π×
R
7
×
1
1
2
π×
R
7
×
C
12
F
P2
=
1
2
π×
R
8
×
C
10
C
12
+C
11
C
12
×
C
11
Detail information is dicussed in application Note AN-
1043 which can be downloaded from the IR Web-Site.
Compensator
Type
Type II (PI)
Type III (PID)
Method A
Type III (PID)
Method B
Table - The compensation type and location of zero
crossover frequency.
Location of Zero
Crossover Frequency
(F
O
)
F
PO
< F
ZO
< F
O
< f
S
/2
F
PO
< F
O
< F
ZO
< f
S
/2
F
PO
< F
O
< f
S
/2 < F
ZO
Typical
Output
Capacitor
Electrolytic,
Tantalum
Tantalum,
Ceramic
Ceramic
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