iru3047 International Rectifier Corp., iru3047 Datasheet - Page 9

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

The master error amplifier is a differential-input transcon-
ductance amplifier. The output is available for DC gain
control or AC phase compensation.
The E/A can be compensated with or without the use of
local feedback. When operated without local feedback
the transconductance properties of the E/A become evi-
dent and can be used to cancel one of the output filter
poles. This will be accomplished with a series RC circuit
from Comp1 pin to ground as shown in Figure 6.
The ESR zero of the LC filter expressed as follows:
The transfer function (Ve / V
The (s) indicates that the transfer function varies as a
function of frequency. This configuration introduces a gain
and zero, expressed by:
The gain is determined by the voltage divider and E/A's
transconductance gain.
Rev. 1.0
09/09/02
F
H(s) = g
|H(s)| =
F
Figure 6 - Compensation network without local
ESR
Z
=
feedback and its asymptotic gain plot.
=
2p3R
(
2p3ESR3Co
V
g
OUT
H(s) dB
m
m
3
R
1
R
3
4
6
5
3C
R
1
V
R
6
REF
Fb1
Gain(dB)
6
R
+ R
9
R
3R
5
5
5
5
)
3R
E/A1
3
OUT
F
4
Z
---(12)
) is given by:
1 + sR
Frequency
---(9)
sC
Comp1
9
R
4
C
---(11)
C
4
9
9
V e
---(10)
www.irf.com
First select the desired zero-crossover frequency (Fo):
Use the following equation to calculate R4:
To cancel one of the LC filter poles, place the zero be-
fore the LC filter resonant frequency pole:
Using equations (12) and (14) to calculate C
One more capacitor is sometimes added in parallel with
C
used to supress the switching noise. The additional pole
is given by:
9
and R
F
R
Where:
V
V
F
F
F
g
R
For:
V
V
F
F
F
R
g
This results to R
F
F
For:
Lo = 6mH
Co = 940mF
Fz = 1.57KHz
R
C
Choose C
F
m
m
O1
O1
ESR
LC(MASTER)
O1
ESR
LC(MASTER)
Z
Z
P
4
IN(MASTER)
OSC
5
IN(MASTER)
OSC
5
4
9
= 10000pF
=
and R
= R
= 10KV
=
= Error Amplifier Transconductance
= 600mmho
> F
= Crossover Frequency for the master E/A
= 15KHz
4
= Zero Frequency of the Output Capacitor
= 8.4KHz
75%F
V
0.753
. This introduces one more pole which is mainly
= Oscillator Ramp Voltage
= 1.25V
2p 3 R
IN(MASTER)
6
ESR
V
= 1KV
6
OSC
9
= Resistor Dividers for Output Voltage
= Maximum Input Voltage
= 12V
= Resonant Frequency of Output Filter
= 2.1KHz
and F
LC(MASTER)
= 10000pF
2p
4
Programming
3
3
O1
F
4
1
=9.8KV. Choose R
L
C
O1
1
C
O
[ (1/5 ~ 1/10)3 f
9
F
9
3F
3 C
3 C
LC
+ C
2
ESR
POLE
O
POLE
3
R
5
R
+ R
5
---(14)
IRU3047
6
4
S
3
=10KV
g
1
9
m
, we get:
---(13)
9