nx2142 Microsemi Corporation, nx2142 Datasheet - Page 14

• Manufacturer Part Number: nx2142
• Description: Single Channel Pwm Controller With Feedforward And 5v Bias Regulator
• Manufacturer: Microsemi Corporation

B. Type II compensator design
power stage output capacitors, usually the Type II
compensator can be used to compensate the sys-
tem.
F
Case 1:
RC circuit as shown in figure 13. R
zero to cancel the double pole effect. C
pole to suppress the switching noise.
the compensator of transconductance amplifier must
satisfy this condition: R
The following equations show the compensator pole
zero location and constant gain.
Rev. 1.1
10/28/07
LC
<F
8. Calculate R
R
Choose R
Choose R
If the electrolytic capacitors are chosen as
For this type of compensator, F
To achieve the same effect as voltage amplifier,
F =
F
ESR
Gain=
Type II compensator can be realized by simple
R =
p
z
3
1
<<F
2
1.2k
2
2
2
V
R
R
R
OUT
O
2
<=1/10~1/5F
3
2
3
1
1
R
-V
=381
V
1
5.3kHz 25nF
=1.2k .
R
1
F
3
1
REF
P1
.
3
REF
1
C
C
C
1
2
3
1.2k
3
>>1/gm and R
s.
5V-0.8V
... (16)
... (15)
... (17)
0.8V
3
and C
O
has to satisfy
2
1
1
introduces a
381
||R
introduce a
2
>>1/gm.
example for type II compensator design, three
1500uF with 19mohm Sanyo electrolytic CAP
6MV1500WGL are used as output capacitors.
Coilcraft DO5010P-152HC 1.5uH is used as output
inductor. The power stage information is that:
V
and ESR zero F
IN
=12V, V
The following parameters are used as an
1.Calculate the location of LC double pole F
Figure 12 - Bode plot of Type II compensator
Figure 13 - Type II compensator with
R1
R2
loop gain
OUT
Vout
power stage
compensator
=1.2V, I
transconductance amplifier(case 1)
F
ESR
Z
Vref
.
Fb
F
R3
LC
OUT
F
gm
=12A, F
ESR
NX2142/2142A
40dB/decade
C2
C1
20dB/decade
F F
S
O
=600kHz.
Ve
Gain
P
LC
14