SC2602L Semtech Corporation, SC2602L Datasheet - Page 12

• Manufacturer Part Number: SC2602L
• Description: Synchronous Voltage Mode Controller
• Manufacturer: Semtech Corporation

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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. 2 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.
(7) An additional capacitor should be reserved at the
compensation pin to ground to have another high fre-
quency pole.
An example is given below to demonstrate the proce-
dure introduced above. The parameters of the power
supply are given as :
The parameters of the power supply are given as :
 2005 Semtech Corp.
POWER MANAGEMENT
Applications Information (Cont.)
R
:=
G
pwm
⋅
1
V
F
L
C o
R c
V bg
V ramp
G m
F zero
C
in
V in
V o
I o
F sw
esr
⋅
G
4 µH
m
<
.
2 π . R . F zero
12 A .
0.02 Ω .
1200 µF
⋅
3.3 V .
1.8 mA
F
12 V .



0.8 V .
200 KHz
o
F
V
1 V .
.
F
<
F o
.
esr
.
o
5
1
.
F


x_over
2
⋅



F
x_over
F
o


⋅



V
V
bg
o


12
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
ensures the loop stability.
F esr
F o
F
F x_over
R 4.8 KΩ
C 65.886 nF
esr
=
=
=
<
=
2.516 KHz
7.958 KHz
F
5
sw
=
20 KHz
SC2602L
www.semtech.com
o
C that