IR3623MPBF_1 IRF [International Rectifier], IR3623MPBF_1 Datasheet - Page 22

• 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]

Fig. 21: The Compensation network for current loop
Compensation
(slave channel)
The
transconductance
configuration the main goal for the slave channel
feedback loop is to control the inductor current to
match the master channel inductor current as
well provides highest bandwidth and adequate
phase margin for overall stability. The following
analysis is valid for both using external current
sense resistors and using DCR of inductor.
The transfer function of power stage is
expressed by:
Where:
V
L
V
As shown the G(s) is a function of inductor
current. The transfer function for compensation
network is given by equation (23), when using a
series RC circuit as shown in figure21.
The loop gain function is:
www.irf.com
2
in
osc
=Output inductor
=Input voltage
D
=Oscillator Peak Voltage
(
s
H
slave
G
)
(
=
(
s
s
V
)
)
R
=
e
=
(
s
s
R
2
H
I
)
L
s
R
V
R
2
2
error
=
( =
(
s
S1
e
*
S2
s
⎛
⎜ ⎜
⎝
)
⎛
⎜ ⎜
⎝
)
g
Fb2
g
=
I
I
m
L2
L1
m
[
G
Vp2
*
sL
*
R
amplifier,
R
(
for
R
R
amplifier
s
2
V
s
1 s
L
* )
s
*
L
2
1 s
in
2
2
V
1
⎞
⎟ ⎟
⎠
⎞
⎟ ⎟
⎠
D
osc
*
*
E/A2
⎛ +
⎜ ⎜
⎝
(
⎛ +
⎜ ⎜
⎝
s
1
1
Current
* )
sC
sC
R
sC
-
sR
- -
s
2
2
Comp2
2
is
2
]
2
R
C
in
( -
2
2
22
⎞
⎟ ⎟
⎠
⎞
⎟ ⎟
⎠
R
differential
C
*
)
2
⎛
⎜ ⎜
⎝
2
2-phase
sL
-
Ve
Loop
- -
2
V
*
( -
in
V
23
osc
⎞
⎟ ⎟
⎠
)
H
Select a zero frequency for current loop (F
1.25 times larger than zero cross frequency for
voltage loop (F
From (24), R2 can be expressed as:
V
V
g
L
R
F
This results to : R
The power stage of current loop has a dominant
pole (Fp) at frequency expressed by:
Where R
stage which includes the R
switches, the DCR of inductor and shunt
resistance (if it used).
R
Set the zero of compensator at 10 times the
dominant pole frequency F
capacitor, C2 can be expressed as:
C
All design should be tested for stability to verify
the calculated values.
(
m
2
o2
in
osc
s1
eq
2
F
=0.34uH
=2800umoh
=0.47nF
=13.2V
O
=125kHz
=DCR=1.1mOhm
=9.4mOhm
2
=1.25V
)
R
=
2
g
=
m
eq
g
*
m
R
is the total resistance of the power
1
*
1 s
R
*
o1
1 s
R
F
R
eq
).
C
O
*
F
2
2
2
F
z
2
2
*
=8.2K
=
P
≅
π
=
=
2
R
=
1
10
π
*
2
.
ds
2
25
F
π
*
(
O
π
on
*
R
F
2
*
V
%
)
F
O
*
eq
IR3623MPbF
*
+
R
in
1
P
2
V
L
*
L
2
*
R
in
2
2
F
*
L
L
P
O
*
2
F
, the compensator
1
+
V
ds(on)
*
z
osc
R
V
s
osc
=
of MOSFET
-
1
- -
( -
-
25
- -
)
( -
o2
24
)
22
)