IR3623MPBF_1 IRF [International Rectifier], IR3623MPBF_1 Datasheet - Page 20

• Manufacturer Part Number: IR3623MPBF_1
• Description: HIGH FREQUENCY 2-PHASE, SINGLE OR DUAL OUTPUT SYNCHRONOUS STEP DOWN CONTROLLER WITH OUTPUT TRACKING AND SEQUENCING
• Manufacturer: IRF [International Rectifier]

To cancel one of the LC filter poles, place the
zero before the LC filter resonant frequency pole:
Using equations (18) and (20) to calculate C9.
One more capacitor is sometimes added in
parallel with C
pole which is mainly used to suppress the
switching noise.
The additional pole is given by:
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 compensation network (typeIII).
The typically used compensation network for
voltage-mode controller is shown in figure 20.
In such configuration, the transfer function is
given by:
The error amplifier gain is independent of the
transconductance under the following condition:
By replacing Z
transformer function can be expressed as:
H
www.irf.com
g
(
s
m
)
*
=
Z
sR
f
F
F
C
For
>>
z
z
6
POLE
=
=
(
C
75
0
1
F
11
1
F
.
P
75
9
P
=
in
%
+
and
V
V
and R
=
<<
π
C
and Z
C
F
*
e
o
LC
2
12
9
*
2
π
F
2
=
=
R
)
π
s
*
*
2
4
g
1
1
4
R
π
f
⎡
⎢
⎣
*
L
1
m
1
. This introduces one more
1
according to figure 15, the
(
4
+
o
F
−
1
*
*
+
*
*
s
R
1
g
+
1
C
g
C
Z
C
sR
−
4
m
sR
9
o
m
in
9
C
*
Z
+
1
Z
*
7
F
>>
9
⎛
⎜ ⎜
⎝
7
C
C
IN
z
C
f
C
C
≅
POLE
POLE
POLE
11
-
11
1
11
- -
π
* )
+
*
*
-(20)
C
[
:
C
1
R
12
12
1
-
+
4
- -
⎞
⎟ ⎟
⎠
sC
*
⎤
⎥
⎦
F
( *
-(21)
10
s
1
(
R
+
6
sR
+
R
8
C
8
)
10
]
)
As known, transconductance amplifier has high
impedance (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 amplifier will not be
able to swing its output voltage over the
necessary range.
The compensation network has three poles and
two zeros and they are expressed as follows:
Cross over frequency is expressed as:
H(s) dB
Fig. 20: Compensation network with local
F
F
F
F
F
P
P
P
Z
1 z
z
2
1
2
3
F
IN
=
o
Gain(dB)
=
=
feedback and its asymptotic gain plot
=
=
=
R
0
2
2
2
2
C
R
π
8
π
π
π
10
7
*
*
*
*
*
F
R
C
C
V
Z
R
R
1
1
1
7
10
OUT
10
8
7
⎛
⎜ ⎜
⎝
*
*
R
*
R
( *
1
1
C
C
C
C
V
6
V
5
11
11
11
R
osc
10
in
F
6
+
*
Z
V
*
+
C
2
C
Fb
REF
2
12
R
12
π
8
⎞
⎟ ⎟
⎠
*
)
IR3623MPbF
≅
1
L
≅
o
R
2
*
2
7
F
π
C
π
E/A
P
o
*
2
*
R
C
1
C
1
7
10
12
*
*
C
R
F
12
C
P
6
Comp
3
11
Frequency
Z
Ve
f
20