iru3046 International Rectifier Corp., iru3046 Datasheet - Page 9

• Manufacturer Part Number: iru3046
• Description: Dual Synchronous Pwm Controller With Current Sharing Circuitry And Ldo 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. 1.9
09/27/02
F
H(s) = g
|H(s)| =
F
Figure 6 - Compensation network without local
ESR
Z
=
feedback and its asymptotic gain plot.
=
2p 3 R
(
V
2p3ESR3Co
g
OUT
H(s) dB
m
m
R
R
3
6
3
5
1
V
R
4
1
REF
Fb1
Gain(dB)
6
3 C
R
R
+ R
6
5
R
3 R
9
5
5
)
E/A1
5
3
OUT
F
3 R
Z
1 + sR
) is given by:
---(12)
Frequency
4
Comp1
sC
---(9)
9
R
4
C
C
4
9
9
---(11)
V e
---(10)
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First select the desired zero-crossover frequency (Fo):
Use the following equation to calculate R
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 suppress 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
R
g
This results to: R
F
F
For:
Lo = 2.2mH
Co = 900mF
Fz = 2.67KHz
R
C
Choose: C
F
O1
O1
ESR
LC(MASTER)
O1
ESR
LC(MASTER)
Z
Z
P
4
IN(MASTER)
OSC
m = Error Amplifier Transconductor
5
IN(MASTER)
OSC
5
6
m = 600mmho
4
9
= 2003pF
=
and R
= 1K
= 200V
= 24.9KV
=
> F
= Crossover Frequency for the master E/A
= 30KHz
4
V
= Zero Frequency of the Output Capacitor
= 25.26KHz
75%F
0.75 3
. This introduces one more pole which is mainly
= Oscillator Ramp Voltage
= 1.25V
2p 3 R
IN(MASTER)
ESR
V
OSC
6
= Resistor Dividers for Output Voltage
= Maximum Input Voltage
= 5V
= Resonant Frequency of Output Filter
= 3.57KHz
9
and F
LC(MASTER)
= 2200pF
2p
4
Programming
3
3
F
O1
1
4
O1
C
=29.7KV. Choose: R
C
L
[ (1/5 ~ 1/10)3 f
F
3F
9
1
9
O
LC
3 C
+ C
3 C
2
ESR
POLE
POLE
3
O
R
5
R
+ R
5
IRU3046
6
---(14)
3
S
4
:
g
4
1
=29.4KV
m
9
, we get:
---(13)
9