NX2422 データシートの表示（PDF） - Microsemi Corporation
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NX2422
Microsemi Corporation
NX2422 Datasheet PDF : 20 Pages
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NX2422
two 1.5uH inductors.
1.Calculate the location of LC double pole FLC
and ESR zero FESR.
FLC = 2× π ×
1
LEFF × COUT
=
1
2×π× 0.75uH×10800uF
= 1.768kHz
FESR
=
1
2 × π × ESR × COUT
=
1
2 × π ×13mΩ ×1800uF
= 6.801kHz
2.Set R2 equal to10kΩ and calculate R1.
R1=
R2 ×
VOUT
VREF
-VREF
= 10kΩ × 0.6V
1.2V-0.6V
= 10kΩ
3. Set crossover frequency FO=15kHz.
4.Calculate R3 value by the following equation.
R3=
VOSC
Vin
×
2 × π × FO × L EFF
ESR
× R2
= 1V × 2 × π × 15kHz × 0.75uH × 10kΩ
12V
2.16m Ω
=27.3kΩ
Choose
R
3
=27.4kΩ.
5. Calculate C by setting compensator zero F
1
Z
at 75% of the LC double pole.
1
C1= 2 × π ×R3 ×Fz
=
1
2× π × 27.4kΩ× 0.75 ×1.768kHz
=4.4nF
Choose C =4.7nF.
1
6.
Calculate
C
2
by
setting
compensator
pole
Fp
at half the swithing frequency.
C2=
π
×
1
R3
×
Fs
=
1
π × 27.4kΩ × 400kH z
=30pF
Choose C2=33pF.
Rev.2.1
12/01/08
B. Type III compensator design
For low ESR output capacitors, typically such as
Sanyo OSCON and POSCAP, the frequency of ESR zero
caused by output capacitors is higher than the cross-
over frequency. In this case, it is necessary to compen-
sate the system with type III compensator.
In design example, six electrolytic capacitors are
used as output capacitors. The system is compensated
with type III compensator. The following figures and equa-
tions show how to realize the this type III compensator
with electrolytic capacitors.
FZ1
=
2×
π
1
× R4
×
C2
FZ2
=
1
2 × π × (R2 + R3 ) × C3
FP1
=
2×
π
1
× R3
×
C3
FP2
=
1
2
×
π
×
R4
×
C1
C1
×
+
C2
C2
...(14)
...(15)
...(16)
...(17)
where FZ1,FZ2,FP1 and FP2 are poles and zeros in
the compensator.
Vout
Zf
Zin
C1
R3
R2
C2 R4
C3
Fb
Ve
R1
Vref
Figure 5 - Type III compensator
11
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