nx2114 Microsemi Corporation, nx2114 Datasheet - Page 12

• Manufacturer Part Number: nx2114
• Description: 300khz & 600khz Synchronous Pwm Controller
• 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 12. R3
and C1 introduce a zero to cancel the double pole
effect. C2 introduces a pole to suppress the switching
noise. The following equations show the compensator
pole zero location and constant gain.
Rev. 4.0
06/20/06
Figure 11- Bode plot of Type II compensator
If the electrolytic capacitors are chosen as power
Type II compensator can be realized by simple
Gain=g
F =
F
z
p
loop gain
2
power stage
compensator
2
m
F
Z
1
R
R +R
1
R
3
1
F
R
3
LC
1
C
C
2
1
F
2
ESR
R
40dB/decade
3
20dB/decade
F F
... (16)
... (15)
... (17)
O
Gain
P
F
an example for type II compensator design, two 680uF
with 41m
and ESR zero F
swithing frequency, here F
LC
<F
Figure 12 - Type II compensator with
For this type of compensator, F
The following uses typical design in figure 19 as
1.Calculate the location of LC double pole F
2.Set R
3. Set crossover frequency at 1/10~ 1/5 of the
4.Calculate R
ESR
R2
R1
final selection of R
F
F
Vout
<<F
LC
ESR
electrolytic capacitors are used.
O
3.5kHz
2
2
2
<=1/10~1/5F
5.7kHz
transconductance amplifier
equal to10.2k . Using equation 18, the
2
2
Vref
Fb
ESR
.
3
value by the following equation.
ESR C
1.5uH 1360uF
20.5m
L
1
OUT
gm
1
1
1
O
1
s.
NX2114/2114A
=30kHz.
is 3.24k
C
OUT
OUT
1360uF
R3
C1
Ve
O
has to satisfy
C2
LC
12