iru3047 International Rectifier Corp., iru3047 Datasheet - Page 10

• Manufacturer Part Number: iru3047
• Description: Dual Synchronous Controller With Current Sharing Circuitry Controller
• Manufacturer: International Rectifier Corp.

IRU3047
The pole sets to one half of switching frequency which
results in the capacitor C
For a general solution for unconditionally stability for any
type of output capacitors, in a wide range of ESR values
we should implement local feedback with a compensa-
tion network. The typically used compensation network
for voltage-mode controller is shown in Figure 7.
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
former function can be expressed as:
H(s)=
10
H(s) dB
C
For F
g
V
V
POLE
m
Figure 7 - Compensation network with local
sR
OUT
Z
e
Z
IN
feedback and its asymptotic gain plot.
f
Gain(dB)
6
>> 1
(C
P
=
=
R
<<
1
C
12
8
1 +
p 3 R
10
1 -
+C
F
IN
f
2
V
S
Z
11
g
g
1
OUT
and Z
)
and
m
m
3
R
R
4
Z
Z
6
5
[
f
IN
3 f
1
1+sR
F
f
Z
V
according to figure 7, the trans-
(1+sR
S
2
Fb1
REF
g
POLE:
- 1
m
7
C
Z
(
IN
9
7
C
C
C
R
>>1
12
11
12
7
F
+C
E/A1
)3[1+sC
C
P
2
11
p 3 R
11
)]
C
12
3(1+sR
1
F
C
4
P
10
---(15)
Comp1
3
3 f
11
(R
Frequency
6
+R
S
8
C
Z
8
)]
V e
10
f
www.irf.com
)
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 (15) regarding transconduc-
tance error amplifier.
1) Select the crossover frequency:
2) Select R
3) Place first zero before LC’s resonant frequency pole.
F
F
F
F
F
Fo < F
F
F
Where:
V
V
Lo = Output Inductor
Co = Total Output Capacitors
C
P1
P2
P3
Z1
Z2
Z1
O1
IN
OSC
11
= 0
=
=
=
=
=
= Maximum Input Voltage
= R
75% F
= Oscillator Ramp Voltage
2p3R
2p3C
2p3R
2p 3 F
2p3R
ESR
7
3C
7
, so that R
and Fo [ (1/10 ~ 1/6)3 f
1
1
LC
10
8
10
7
3C
7
3C
1
3
3
3(R
Z1
1
(
1
3 R
V
10
11
V
C
C
OSC
6
IN
12
+ R
12
7
3C
7
+C
3
>>
8
)
11
2p3Lo3Co
11
)
g
2
m
2p3C
1
2p3R
1
10
S
3R
1
7
3C
6
12
---(16)
09/09/02
Rev. 1.0