nx2142 Microsemi Corporation, nx2142 Datasheet - Page 13

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

Case 2:
capacitors, typical design example of type III
compensator in which the crossover frequency is
selected as F
as the following steps. Here one SANYO 6ME-WG1000
with 30 m
inductor is 6.8uH.
and ESR zero F
Rev. 1.1
10/28/07
8. Calculate R
Choose R
Figure 11 - Bode plot of Type III compensator
1. Calculate the location of LC double pole F
R =
F
If electrolytic capacitors are used as output
loop gain
power stage
compensator
LC
1
V
F
R
1.93kHz
F
2
2
OUT
Z1
LC
2
LC
is chosen as output capacitor, output
<F
<F
F
1
-V
=5.7k
(F
ESR
V
Z2
F
F
ESR
ESR
REF
1
ESR
REF
LC
LC
.
.
6.8uH 1000uF
L
<F
<F
<F
F
1
OUT
P1
40dB/decade
O
1
ESR
O
(for electrolytic capacitors)
and F
20k
<F
F
C
5V-0.8V
O
OUT
O
)
O
20dB/decade
<=1/10~1/5F
0.8V
F
P2
5.7k
s
is shown
LC
double pole by equation (11).
half the switching frequency.
1/10~ 1/5 of the switching frequency. Set F
2. Set R
3. Calculate C2 with zero Fz1 at 75% of the LC
Choose C
4. Calculate C
Choose C
5. Calculate C
Choose C
6. Set zero F
Choose R
7. Calculate R
C
F
R =
C
C =
ESR
2
1
2
3
=
=2k
=
= 2 5 n F
2
2
2
10nF
2
2
53pF
2
1 0
V
5.3kHz
2
2
1
V
4
O S C
1
in
equal to 10k
2
1
3
1
2
=10nF.
=52pF.
=25nF.
=20k
C
25nF
0.75 1.93kHz 10k
1
F
3 0 m
R
1
10k
3
Z2
ESR C
30m
Z1
1
3
3
4
E S R
1
= F
by equation (14) with pole F
with the crossover frequency at
by equation (13) with F
(
R
1
6 0 k H z
F
1
F
1
z2
LC
(
4
P2
1
1.93kHz 5.3kHz
F
NX2142/2142A
-
300kHz
and F
1000uF
O
OUT
1 0 k
F
R
1
p1
1
4
L
)
p1
6 . 8 u H
F
-
=F
P 1
5 . 3 k H z
ESR
1
, calculate R
O
)
=60kHz.
p1
=F
p2
ESR
13
at
.
2.