NX2116A MICROSEMI [Microsemi Corporation], NX2116A Datasheet - Page 11

• Manufacturer Part Number: NX2116A
• Description: SYNCHRONOUS PWM CONTROLLER WITH CURRENT LIMIT, POWER GOOD & OVER VOLTAGE
• Manufacturer: MICROSEMI [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 7. 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. 3.0
03/14/06
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
NX2116/2116A/2116B/2117/2117A
1
2
F
tor design. Input voltage is 12V, output voltage is 1.8V,
output inductor is 1uH, 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
electrolytic capacitors.
O
2
2.9kHz
2
<=1/10~1/5F
2
-V
transconductance amplifier
equal to 1k .
8.2kHz
V
2
2
Vref
1
Fb
REF
ESR
=806
REF
.
3
value by the following equation.
ESR C
6.5m
1uH 3000uF
1k
L
1.8V-0.8V
gm
1
1
OUT
1
O
1
s.
=60kHz.
0.8V
C
OUT
OUT
3000uF
R3
C1
800
Ve
O
has to satisfy
C2
LC
11