iru3046 International Rectifier Corp., iru3046 Datasheet - Page 11

• Manufacturer Part Number: iru3046
• Description: Dual Synchronous Pwm Controller With Current Sharing Circuitry And Ldo 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. 1.9
09/27/02
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 (16) and calculate C
REF
8
- V
>
1
1
REF
1
g
7
1
7
m
3 F
R
selection.
3 R
7
P3
P2
Z2
O
6
3 Co
- R
8
7
and start from step 2.
3
5
:
10
V
:
V
OSC
IN
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:
H(s)=[G(s) 3 D(s) 3 R
H(s)=R
Select a zero crossover frequency (F
switching frequency:
G(s) =
Where:
V
V
L
V
F
F
2
O2
O2
IN
OUT
OSC
= Output Inductor
R
S2
Figure 8 - The PI compensation network
= Input Voltage
=
= 20KHz
S2
3
= Output Voltage
= Oscillator Peak Voltage
Ve(s)
10
3 I
(
f
S
g
Ve(s)
I
L2
m
R
(s)
L2
R
3
S1
(s)
S2
R
R
Fb2
I
I
=
=
for slave channel.
L2
L1
S1
S2
Vp2
(
)
sL
g
V
3
S2
m
L
L
IN
2
]
3
2
1
(
3 V
- V
1+sR
E/A2
R
R
OUT
S1
S2
sC
OSC
)
2
2
3
C
Comp2
(
2
)
1 + sC
O2
3
R
) one-tenth of the
IRU3046
---(17)
C
(
sC
2
2
sL
V
2
V e
2
IN
2
R
3V
-V
2
)
OUT
OSC
---(18)
)
11