IR3822 International Rectifier Corp., IR3822 Datasheet - Page 15

• Manufacturer Part Number: IR3822
• Description: Tm Supirbuck Highly Integrated 4a Wide-input Voltage, Synchronous Buck Regulator
• Manufacturer: International Rectifier Corp.

01/08/08
Based on the frequency of the zero generated by
the output capacitor and its ESR versus
crossover frequency, the compensation type can
be different. The table below shows the
compensation types and location of crossover
frequency.
Table1- The compensation type and location
The details of these compensation types are
discussed in application note AN-1043 which can
be downloaded from IR’s website at www.irf.com.
For this design we have:
V
V
V
V
g
L
C
F
These result to:
F
F
F
Select crossover frequency:
Fo=80kHz
Since: F
selected to place the poles and zeros.
The following design rules will give a crossover
frequency
switching frequency. The higher the band width,
the potentially faster the load transient response.
F
Compensator
type
m
o
in
o
osc
ref
s
LC
ESR
s/2
o
o
Type III(PID)
Type III(PID)
=1.5uH
=600kHz
=1.8V
=1000umoh
=4x22uF, ESR=0.8mOhm
=12V
Method A
Method B
=0.6V
<
Typ II(PI)
=18.76kHz
=300kHz
=1.25V
=4.4MHz
F
ESR
and
LC
<F
of F
approximately
F
o
o
<F
≤
ESR
F
F
F
(
1/5
s/2
LC
LC
LC
<F
F
versus F
<F
<F
<F
~
ESR
ESR
1/10
ESR
o
o
<F
<F
vs. F
, typeIII method B is
<F
ESR
s/2
)
*
o
<F
o
F
one-tenth
<F
<F
s
o
ESR
s/2
s/2
Output
capacitor
Electrolytic
, Tantalum
Tantalum,
Ceramic
ceramic
of
the
The DC gain will be large enough to provide high
DC-regulation accuracy (typically -5dB to -12dB).
The phase margin should be greater than 45
overall stability.
Desired Phase Boost:
Calculate
C
C
Calculate
F
F
F
F
Select
Select
R
Select
R
Select
R
R
Z
Z
P
P
10
3
4
3
8
9
2
2
2
2
=
=
=
=
=
=
=
=
=
=
V
2
2
14
2
2
F
F
453
2
π
π
o
π
π
o
o
π
V
:
:
:
:
*
1 .
*
C
R
*
*
R
*
*
ref
F
*
V
7 .
kHz
7
3
1
F
F
10
C
F
Z1
C
1
1
C
R
ref
1
1
1
1
1
Z1
P
=
o
kHz
=
7
7
=
3
=
C
4
10
+
*
+
-
*
-
180pF
*
*
21K
*
*
. 1
7
and
Sin
,
Sin
0
L
Sin
Sin
F
R
R
R
R
F
*
o
5 .
96
Z
P
8
*
V
8
2
3
3
2
;
Θ
Θ
Ω
Θ
Θ
*
;
C
in
;
and
C
K
;
R
C
C
F
o
R
3
Ω
R
9
4
Z
3
*
10
:
10
2
=
V
=
=
R
;
IR3822MPBF
=
30
OSC
1.07nF,
25
and
9
R
. 1
:
8
.
.
20
Θ
,
95
26
=
R
max
60
K
K
F
3
pF
=
, Ω
, Ω
P3
.
=
20
72
Select
,
=
70
check
.
Select
94
K
0.5
Select
, Ω
o
KΩ
PD-60333
*
:
F
Select
,
R
s
C
:
:
check
10
R
4
C
9
≥
=
3
=
=
1
g
1
:
0 .
30
22
m
R
o
R
nF
8
1 .
3
for
pF
15
=
K
≥
60
Ω
g
2
m
4 .
K
Ω