nx2154 Microsemi Corporation, nx2154 Datasheet - Page 11

• Manufacturer Part Number: nx2154
• Description: 300khz 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.
circuit without feedback as shown in figure 6. R
introduce a zero to cancel the double pole effect. C
introduces a pole to suppress the switching noise. The
following equations show the compensator pole zero lo-
cation and constant gain.
Rev.1.2
02/26/07
Figure 6 - Bode plot of Type II compensator
If the electrolytic capacitors are chosen as power
Type II compensator can be realized by simple RC
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
3
and C
1
2
F
tor design. Input voltage is 40V, output voltage is 5V,
output inductor is 6uH, output capacitor is one 1000uF
with 30m
and ESR zero F
swithing frequency, here F
LC
<F
Figure 7 - Type II compensator with
R =
For this type of compensator, F
The following is parameters for type II compensa-
1.Calculate the location of LC double pole F
2.Set R
Choose R
3. Set crossover frequency at 1/10~ 1/5 of the
4.Calculate R
F
ESR
R2
R1
1
ESR
Vout
<<F
V
F
R
LC
OUT
2
electrolytic capacitors.
5.3kHz
2
2
O
2
<=1/10~1/5F
transconductance amplifier
equal to 1k .
-V
V
1.3kHz
Vref
2
2
1
Fb
REF
ESR
=191
REF
.
ESR C
30m
3
value by the following equation.
1
1k
gm
15uH 1000uF
1
L
5V-0.8V
1
OUT
O
1
s.
NX2154/2154A
1000uF
=30kHz.
OUT
0.8V
C
OUT
R3
C1
Ve
191
O
has to satisfy
C2
LC
11