nx2119 Microsemi Corporation, nx2119 Datasheet - Page 11
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nx2119
Manufacturer Part Number
nx2119
Description
Synchronous Pwm Controller With Current Limit Protection
Manufacturer
Microsemi Corporation
Datasheet
1.NX2119.pdf
(16 pages)
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