NX2142ACUTR datasheet(12/18 Pages) MICROSEMI

12 / 18 page

NX2142/2142A

Rev. 1.1

10/28/07

Case 1:

LC<FO<FESR(for most ceramic or low

ESR POSCAP, OSCON)

40dB/decade

20dB/decade

loop gain

ESR

compensator

power stage

FZ1 Z2

FP2

Figure 10 - Bode plot of Type III compensator

LC<FO<FESR)

Typical design example of type III compensator

in which the crossover frequency is selected as

LC<FO<FESR and FO<=1/10~1/5Fs is shown as the

following steps. Here two X5R 22uF ceramic capacitor

wit

h3m

Ω is chosen as output capacitor, output inductor

is 6.8uH.

1. Calculate the location of LC double pole F

and ESR zero F

ESR.

OUT

6.8uH

44uF

9.2kHz

×π ××

ESR

OUT

ESRC

1.5m

44uF

241kHz

×π ××

×π ×

Ω×

2. Set R

4 equal to 10kΩ.

3. Calculate C2 with zero Fz1 at 50% of the LC

double pole by equation (11).

Z14

0.5

9.2kHz

10k

3.5nF

×π ××

×π ×

×Ω

Choose C

2=3.9nF.

4. Calculate C

1 by equation (14) with pole Fp2 at

half the switching frequency.

10k

300kHz

53pF

×π ××

×π ×

Ω×

Choose C

1=52pF.

5. Calculate C

3 with the crossover frequency at

1/10~ 1/5 of the switching frequency. Set F

O=60kHz.

OSCO

out

in4

C =C

60kHz

6.8uH

44uF

10k

=1.1nF

×π ××

××

×π ××

××

Ω

Choose C

3=1.2nF.

6. Set zero F

Z2 = 0.75FLC and Fp1 =0.5Fs, calcu-

late R

R =

(-)

(

1.2nF

0.75*9.2kHz 300kHz

=18k

×π×

Ω

Choose R

2=20kΩ.

7. Calculate R

3 by equation (13) with Fp1 =Fs.

P13

600kHz 1.2nF

221

×π ××

=Ω

Choose R

3 =300Ω.

NX2142ACUTR Datasheet(PDF) 12 Page - Microsemi Corporation

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