ir3841 International Rectifier Corp., ir3841 Datasheet - Page 22

• Manufacturer Part Number: ir3841
• Description: Integrated 8a Synchronous Buck Regulator
• Manufacturer: International Rectifier Corp.

Detailed calculation of compensation TypeIII
02/09/09
Desired
F
F
Select
F
Select
Calculate
R
Select
C
C
Calculate
R
R
Select
R
P
P
Z
3
4
3
10
8
9
2
2
3
=
=
=
=
=
=
=
=
=
V
2
2
2
2
F
0.5
F
2
π
π
π
π
:
:
:
:
o
π
o
o
V
C
R
F
R
*
*
*
*
-
ref
7
*
Z
8
*
V
F
3
F
C
F
Phase
1
1
1
1
1
C
1
F
ref
=
o
1
P
Z
1
=
R
=
R
−
+
+
−
7
1
=
s
1
3
7
C
*
10
2.2
3
*
4.02
sin
sin
3.01
sin
sin
*
*
*
0
,
=
*
L
7
F
,
.
R
R
F
C
o
R
5
Z
300
*
R
P
nF
3
2
Θ
Θ
Θ
3
V
3
8
Θ
*
*
2
8
;
k
;
k
C
in
;
F
-
C
R
Margin
and
;
Ω
C
Ω
=
=
Z
R
and
o
3
9
2
4
kHz
R
17.63
10
567.1
*
=
=
=
=
10
V
;
C
176.25
2.56
osc
6
R
8.82
R
=
4
8
nF,
9
128
:
;
kHz
kHz
Θ
=
R
:
k
3.97
3
=
Ω
kHz
Select
=
Ω
70
pF
,
3.05
Select
o
,
k
Select
and
Ω
Select
,
:
k
C
:
Ω
4
R
:
R
=
9
:
C
10
10
=
3
2.55
=
=
nF
130
150
k
Ω
Ω
pF
Setting the Power Good Threshold
Power Good threshold is internally set at 88% of
Vref. When the voltage at the FB pin exceeds the
threshold, PGood is asserted.
The PGood is an open drain output. Hence, it is
necessary to use a pull up resistor R
PGood pin to Vcc.
resistor must be chosen such as to limit the
current flowing into the PGood pin, when the
output voltage is not in regulation, to less than 5
mA. A typical value used is 4.7kΩ.
Programming the Current-Limit
The Current-Limit threshold can be set by
connecting a resistor (R
to the OCSet pin. The resistor can be calculated
by using equation (4). This resistor ROCSET
must be placed close to the IC.
The
coefficient and it should be considered for the
worst case operation.
I
SET
R
I
(50%
I
R
OCSet
SET
DS
OCSet
=
(
R
on
I
≅
L
DS(on)
)
=
(
I
critical
over
=
o
=
59.07
(
LIM
2.65
8.7
)
)
=
=
mΩ
nominal
has
μA
kΩ
R
8
OCSet
A
*
R
*
1.5
(at
Select
DS
1.5
IR3841MPbF
a
The value of the pull-up
∗
(
=
F
on
I
OCSET
OCSet
=
s
13.05
output
)
12
positive
=
R
600
A
7
) from the SW pin
..........
mΩ
=
kHz)
2.67
current
..........
temperature
kΩ
PG
)
...
(32)
22
from