IR3651STRPBF International Rectifier, IR3651STRPBF Datasheet - Page 16

• Manufacturer Part Number: IR3651STRPBF
• Description: IC CTLR PWM SYNC DC-DC 14SOIC
• Manufacturer: International Rectifier

Specifications of IR3651STRPBF

• Pwm Type: Voltage Mode
• Number Of Outputs: 1
• Frequency - Max: 460kHz
• Duty Cycle: 80%
• Voltage - Supply: 4.5 V ~ 13.2 V
• Buck: Yes
• Boost: No
• Flyback: No
• Inverting: No
• Doubler: No
• Divider: No
• Cuk: No
• Isolated: No
• Operating Temperature: 0°C ~ 125°C
• Package / Case: 14-SOIC (3.9mm Width), 14-SOL
• Frequency-max: 460kHz
• Package: 14-Pin SOIC (NB)
• Circuit: Sync PWM Controller
• Vcc (min): 4.5
• Vcc (max): 13.2
• Iout (a): 25
• Switch Freq (khz): programmable to 400kHz
• Pbf: PbF Option Available
• For Use With: IRDC3651 - KIT REF DESIGN SYNCH BUCK REG
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

To cancel one of the LC filter poles, place the
zero before the LC filter resonant frequency pole:
Using equations (15) and (16) to calculate C
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 15.
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
12/07/2010
(
s
g
)
m
=
*
sR
Z
C
For
f
F
F
8
POLE
z
z
>>
(
C
=
=
1
F
4
75
0
1
P
F
=
4
+
in
.
P
75
<<
%
and R
π
C
and
and Z
V
V
=
3
F
*
*
e
o
2
)
LC
F
2
R
2
π
*
s
=
π
3
⎡
⎢
⎣
*
3
1
(
*
f
1
1
g
1
. This introduces one more
R
1
according to figure 15, the
F
L
+
1
m
3
+
+
o
s
−
sR
*
*
*
sR
−
1
g
C
C
g
C
Z
C
3
4
m
1
o
4
m
3
in
⎛
⎜ ⎜
⎝
C
+
4
Z
*
Z
C
C
>>
C
4
C
IN
≅
f
POLE
4
* )
4
POLE
POLE
-
+
*
π
1
-(16)
[
C
1
C
*
:
3
3
+
R
1
⎞
⎟ ⎟
⎠
sC
3
⎤
⎥
⎦
-
*
( *
-(17)
7
F
(
1
s
R
+
8
4
sR
+
.
R
10
10
C
)
7
]
)
H(s) dB
As known, transconductance amplifier has high
impedance (current source) output, therefore,
consideration should be taken when loading the
error amplifier 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:
F
F
F
F
F
Fig.15: Compensation network with local
Z
P
P
P
1 z
z
2
1
2
3
IN
Gain(dB)
=
=
=
=
=
F
R
feedback and its asymptotic gain plot
0
2
2
2
2
o
C
10
π
π
π
π
=
7
*
F
*
*
*
R
R
C
Z
R
R
1
3
V
1
1
3
7
*
10
3
O
C
⎛
⎜ ⎜
⎝
*
( *
R
1
R
1
*
C
C
C
7
8
9
C
R
*
4
4
4
F
7
8
V
+
V
*
Z
osc
V
+
C
in
C
2
Fb
REF
R
3
3
*
10
⎞
⎟ ⎟
⎠
2
)
π
≅
≅
IR3651SPBF
*
2
R
1
L
2
π
3
F
o
E/A
π
P
*
*
2
C
*
R
1
C
o
1
C
3
7
*
3
*
C
R
F
3
C
8
P
Comp
3
4
Frequency
Z
Ve
f
16