ir3831 International Rectifier Corp., ir3831 Datasheet - Page 21

• Manufacturer Part Number: ir3831
• Description: Synchronous Buck Regulator For Ddr Applications
• Manufacturer: International Rectifier Corp.

Detailed calculation of compensation TypeIII
02/20/09
Desired
F
F
Select
F
Select
Calculate
R
Select
C
C
Calculate
R
R
Select
Z
P
P
3
10
3
4
8
2
3
2
=
=
=
=
=
=
=
=
2
2
2
2
F
0.5
F
2
π
:
:
π
:
π
π
:
π
o
o
C
R
F
R
*
*
*
*
7
*
Z
8
*
F
C
F
3
1
F
Phase
1
1
1
1
C
1
F
P
=
o
1
1
=
Z
R
=
R
7
−
+
+
−
1
=
s
1
7
3
C
*
3
10
2.2
1.47
*
6.65
sin
sin
sin
sin
*
*
*
0
,
=
L
7
F
,
R
.
R
F
C
o
5
Z
200
*
R
P
nF
3
2
Θ
Θ
Θ
Θ
3
V
3
*
*
2
8
;
k
k
C
in
;
F
-
C
Margin
and
;
C
Ω
Ω
=
=
Z
and
R
o
3
2
4
kHz
R
10.58
10
340.28
*
=
=
=
10
V
;
C
541.34
osc
20.47
R
5.29
R
=
4
8
9
215
:
;
Θ
=
R
:
kHz
6.63
kHz
3
=
kHz
nF,
=
70
pF
Ω
1.48
,
,
o
k
Select
Select
and
Ω
Select
,
k
Ω
:
:
:
R
C
C
10
4
3
=
=
=
22
560
210
nF
pF
Ω
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 R
be placed close to the IC.
The
coefficient and it should be considered for the
worst case operation.
Setting the Power Good Threshold
Power Good threshold is internally set at 0.515 V.
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.
I
SET
R
I
(50%
I
R
OCSet
SET
DS
OCSet
=
R
(
I
DS(on)
on
L
≅
(
)
=
critical
over
I
=
o
=
39.22
(
LIM
3.99
8.7
)
)
=
has
nominal
m
=
k
μA
R
Ω
Ω
8
OCSet
A
*
R
(at
Select
1.5
*
DS
a
1.5
IR3831MPbF
The value of the pull-up
∗
(
F
OCSET
on
=
I
OCSet
output
s
positive
)
13.05
=
=
12
R
400
) from the SW pin
7
A
..........
m
=
kHz)
current)
Ω
4.02
temperature
..........
OCSET
k
Ω
PG
...
must
(32)
21
from