nx2113 Microsemi Corporation, nx2113 Datasheet - Page 13

• Manufacturer Part Number: nx2113
• Description: 300khz & 600khz Synchronous Pwm Controller With Programmable Bus Uvlo
• Manufacturer: Microsemi Corporation

B. Type II compensator design
stage output capacitors, usually the Type II compensa-
tor can be used to compensate the system.
RC circuit without feedback as shown in figure 11. R3
and C1 introduce a zero to cancel the double pole
effect. C2 introduces a pole to suppress the switching
Rev. 2.0
11/18/05
Figure 12 - Bode plot of Type II compensator
loop gain
If the electrolytic capacitors are chosen as power
Type II compensator can be realized by simple
Figure 11 - Type II compensator with
power stage
compensator
R2
R1
Vout
F
Z
F
Vref
LC
Fb
transconductance amplifier
F
ESR
40dB/decade
20dB/decade
gm
F F
O
Gain
P
R3
C1
Ve
C2
noise. The following equations show the compensator
pole zero location and constant gain.
F
an example for type II compensator design, two 680uF
with 36m
and ESR zero F
swithing frequency, here F
LC
<F
R =
2.Set R
For this type of compensator, F
The following uses typical design in figure 18 as
1.Calculate the location of LC double pole F
3. Set crossover frequency at 1/10~ 1/5 of the
4.Calculate R
Choose R
ESR
R
3
=
=10.3k
1
F
F =
F
Gain=g
12V
<<F
F
ESR
2V
V
z
p
LC
V
OSC
10k
in
electrolytic capacitors are used.
2
2.5V-0.8V
2
2
O
10k +4.7k
<=1/10~1/5F
equal to10k . Using equation 18.
2.0kHz
2
2
2
6.5kHz
2
2
m
2
ESR
3
4.7k
=10k
1
R
0.8V
R +R
1
R
.
3
R
3
1
value by the following equation.
R
3
ESR
30kHz 4.7uH
18m
18m
F
ESR C
1
L
4.7uH 1360uF
C
O
C
1
OUT
2
1
1
2
4.7k
1
L
O
1
s.
NX2113/2113A
R
=30kHz.
C
3
g
OUT
1
1360uF
m
OUT
... (16)
... (15)
... (17)
R +R
1
R
O
2.5mA/V
1
has to satisfy
2
1
LC
13