nx2119 Microsemi Corporation, nx2119 Datasheet - Page 11

• Manufacturer Part Number: nx2119
• Description: Synchronous Pwm Controller With Current Limit Protection
• 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.3.2
04/10/08
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 5V, output voltage is 1.8V,
output inductor is 1.5uH, output capacitors are two
1500uF with 13m
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
ESR
R2
R1
1
F
F
Vout
<<F
LC
ESR
V
R
OUT
2
O
2.3kHz
2
2
2
<=1/10~1/5F
-V
transconductance amplifier
equal to 1k .
8.2kHz
V
2
2
Vref
1
Fb
REF
ESR
=800
REF
.
3
electrolytic capacitors.
value by the following equation.
1.5uH 3000uF
L
ESR C
6.5m
1k
1.8V-0.8V
1
OUT
gm
1
1
O
1
s.
NX2119/2119A
=30kHz.
C
0.8V
OUT
OUT
3000uF
R3
C1
800
Ve
O
has to satisfy
C2
LC
11