iru3047 International Rectifier Corp., iru3047 Datasheet - Page 11

• Manufacturer Part Number: iru3047
• Description: Dual Synchronous Controller With Current Sharing Circuitry Controller
• Manufacturer: International Rectifier Corp.

4) Place third pole at the half of the switching frequency.
5) Place R
6) Place second pole at ESR zero.
7) Place second zero around the resonant frequency.
8) Use equation (1) to calculate R
These design rules will give a crossover frequency ap-
proximately one-tenth of the switching frequency. The
higher the band width, the potentially faster the load tran-
sient speed. The gain margin will be large enough to
provide high DC-regulation accuracy (typically -5dB to -
12dB). The phase margin should be greater than 458 for
overall stability.
The slave error amplifier is a differential-input transcon-
ductance amplifier as well, the main goal for the slave
feed back loop is to control the inductor current to match
the masters inductor current as well provides highest
bandwidth and adequate phase margin for overall stabil-
ity.
Rev. 1.0
09/09/02
F
C
C
If not, change R
C
F
R
Check if R
If R
F
R
R
P3
P2
Z2
12
12
10
8
6
5
=
=
=
= F
8
= F
=
=
> 50pF
[
is too small, increase R
2p 3 C10 3 F
2p 3 C10 3 F
V
f
2
2p 3 R
ESR
LC
S
OUT
2p 3 Lo 3 F
7
V
in equation (16) and calculate C
REF
8
- V
>
1
1
REF
1
7
g
1
7
3 F
m
R
selection.
3 R
7
P3
P2
Z2
O
6
3 Co
- R
8
7
and start from step 2.
3
5
:
V
V
OSC
IN
10
:
www.irf.com
The transfer function of power stage is expressed by:
As shown the transfer function is a function of inductor
current.
The transfer function for the compensation network is
given by equation (18), when using a series RC circuit
as shown in Figure 8.
D(s)=
The loop gain function is:
Select a zero crossover frequency (F
switching frequency:
G(s) =
Where:
V
V
L
V
H(s)=[G(s)3D(s)3R
H(s)=R
F
F
2
O2
O2
IN
OUT
OSC
R
= Output Inductor
Figure 8 - The PI compensation network
= Input Voltage
S2
=
= 20KHz
Ve(s)
= Output Voltage
= Oscillator Peak Voltage
3 I
10
f
S2
S
Ve(s)
I
3
L2
L2
R
R
(s)
(
(s)
S2
S1
g
m
Fb2
= g
I
I
3
L2
L1
=
for slave channel.
(
Vp2
R
R
sL
m
V
S1
S2
3
L
L
IN
2
2
1
)
S2
3 V
- V
R
R
3
E/A2
]
S1
S2
(
OUT
) (
1+sR
OSC
3
sC
Comp2
1 + sC
2
2
C
O2
2
sC
R
)
) one-tenth of the
C
IRU3047
---(17)
2
3
2
2
2
(
V e
R
sL
2
V
)
IN
2
3V
-V
---(18)
OUT
OSC
11
)