12

 2005 Semtech Corp.

www.semtech.com

POWER MANAGEMENT

SC2602L

or

R

1

⋅

⋅











2

⋅











⋅











⋅

:=

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 :

<

<

F zero

F o

5

C

1

2

π

. R

. F

zero

.

The parameters of the power supply are given as :

Step 1. Output filter corner frequency

Step 2. ESR zero frequency:

Step 3. Check the following condition:

5

<

Which is satisfied in this case.

Step 4. Choose crossover frequency and calculate

compensator R:

R4.8 K

Ω

=

Step 5. Calculate the compensator C:

Step 6. Generate Bode plot and check the phase mar-

ensures the loop stability.

Applications Information (Cont.)

V in 12 V

.

V o 3.3 V

.

I o 12 A

.

F sw 200 KHz

.

L4

µH

.

C o 1200 µF

.

R c 0.02 Ω

.

V bg

0.8 V

.

V ramp 1V

.

G m

1.8 mA

.

V

F o 2.516 KHz

=

F esr 7.958 KHz

=

F x_over 20 KHz

=

C

65.886 nF

=