sc2450 Semtech Corporation, sc2450 Datasheet - Page 17

• Manufacturer Part Number: sc2450
• Description: Sc2450 Bi-phase/dual Controller
• Manufacturer: Semtech Corporation

or
when
(5) The compensation capacitor is determined by choos-
ing the compensator zero to be about one fifth of the
output filter corner frequency:
(6) The final step is to generate the Bode plot, either by
using the simulation model in Fig. 1 or using the equa-
tions provided here with Mathcad. The phase margin
can then be checked using the Bode plot. Usually, this
design procedure ensures a healthy phase margin.
An example is given below to demonstrate the proce-
dure introduced above. The parameters of the power
supply are given as:
POWER MANAGEMENT
Control Loop Design (Cont.)
2007 Semtech Corp.
R
G pwm V in G error
F esr F o F x_over
F zero
C
1
F
C
2
R
R
R
sw
V
V
o
I
1
2
L := 4 H
c
o
o
R F zero
:= 3000 F
in
F o
:= 150 KHz
:= 0.02
:= 1.5 K
:= 1.0 K
5
1
:= 2.5 V
:= 20 A
:= 24 V
F esr
F o
2
F x_over
F o
V bg
V o
17
Step 1. Output filter corner frequency
Step 2. ESR zero frequency:
Step 3. Check the following condition:
Which is satisfied in this case.
Step 4. Choose crossover frequency and calculate
compensator R:
Step 5. Calculate the compensator C:
Step 6. Generate Bode plot and check the phase mar-
gin. In this case, the phase margin is about 85°C that
ensures the loop stability. Fig. 2 shows the Bode plot of
the loop.
F
F ers
F
F
esr
C = 92.98 nF
o
x_over
R = 5.89 K
= 1.453 KHz
= 2.653 KHz
<
F sw
= 30 KHz
5
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