NX2415 Просмотр технического описания (PDF) - Microsemi Corporation
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NX2415
Microsemi Corporation
NX2415 Datasheet PDF : 21 Pages
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NX2415
The transfer function of type III compensator
is given by:
[ ] Ve
VOUT
=
sR2
1
×(C2
+
C1)
×
(1+ sR4 ×C2)× 1+ s(R2 + R3)×C3
(1+
sR4
×
C2
C2
×
+
C1
C1
)
×
(1+
sR3
×
C3
)
6. Calculate R4 by choosing FO=40kHz.
R4 =
VOSC
Vin
×
2 × π × FO × LEFF
ESR
×
R2
R2
× R3
+ R3
= 1V × 2 × π × 40kHz × 0.34uH × 10kΩ × 3.92kΩ
12V
3.5mΩ
10kΩ + 3.92kΩ
=5.73kΩ
Use the same power stage requirement as demo
board. The crossover frequency has to be selected as
F <F <F , and usually F <=1/10~1/5F .
LC ESR O
O
S
1.Calculate the location of LC double pole F
LC
and ESR zero F .
ESR
FLC = 2× π ×
1
LEFF × COUT
=
1
2× π × 0.34uH× 2000uF
= 6.1kHz
FESR
=
1
2 × π × ESR × COUT
=
1
2 × π × 3.5mΩ × 2000uF
= 22.7kHz
2.Set R2 equal to10kΩ.
R1=
R2 ×
VOUT
VREF
-VREF
= 10kΩ × 0.8V
1.2V-0.8V
= 20kΩ
Choose R1= 20kΩ.
3. Calculate C3 by setting FZ2 = FLC and Fp1 =FESR.
C3
=
2
×
1
π×
R
2
×( 1
Fz2
-
1
Fp1
)
=
1
×( 1 - 1 )
2 × π ×10kΩ 6.1kHz 22.7kHz
=1.9nF
Choose C3=1.8nF.
5. Calculate R by equation (13).
3
Choose R4=5.62kΩ.
7. Calculate C2 with zero Fz1 at 75% of the LC
double pole by equation (11).
C2
=
1
2 × π × FZ1 × R4
=
1
2 × π × 0.75 × 6.1kHz × 5.62kΩ
= 6.2nF
Choose C =6.8nF.
2
8. Calculate C by equation (14) with pole F at
1
p2
half the switching frequency.
C1
=
2×π
1
× R4
× FP2
=
1
2 × π × 5.62kΩ × 200kHz
= 141pF
Choose C1=150pF.
B. Type II compensator design
If the electrolytic capacitors are chosen as power
stage output capacitors, usually the Type II compensa-
tor can be used to compensate the system.
Type II compensator can be realized by simple RC
circuit without feedback as shown in figure 4. R3 and C1
introduce a zero to cancel the double pole effect. C2
introduces a pole to suppress the switching noise. The
following equations show the compensator pole zero lo-
cation and constant gain.
R3
=
1
2 × π × FP1 × C3
=
1
2 × π × 22.7kHz ×1.8nF
= 3.89kΩ
Choose R3=3.92kΩ.
Gain= R3
R2
1
Fz = 2 × π × R3 × C1
Fp
≈
1
2 × π × R3
× C2
... (15)
... (16)
... (17)
Rev.4.8
11
05/06/08
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