NX2116A datasheet(9/14 Pages) MICROSEMI

9 / 14 page

NX2116/2116A/2116B/2117/2117A

Rev. 3.0

03/14/06

Case 1:

LC<FO<FESR

40dB/decade

20dB/decade

loop gain

ESR

compensator

power stage

FZ1 Z2

FP2

Figure 4 - Bode plot of Type III compensator

Design example for type III compensator are in

order. The crossover frequency has to be selected as

LC<FO<FESR, and FO<=1/10~1/5Fs.

1.Calculate the location of LC double pole F

and ESR zero F

ESR.

OUT

1uH

440uF

7.6kHz

×π ××

ESR

OUT

ESRC

440uF

60.3kHz

×π ××

×π ×

Ω×

2. Set R

2 equal to 20kΩ.

Ω×

=Ω

REF

OUT

REF

20k

0.8V

R =

16k

-V

1.8V-0.8V

Choose R

1=16kΩ.

3. Set zero F

Z2 = FLC and Fp1 =FESR .

4. Calculate R

4 and C3 with the crossover

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

O=50kHz.

C =

(-)

(

20k

7.6kHz 60.3kHz

=916pF

×π×

×π×Ω

OSCO

out

in3

R =C

1.5V

50kHz 1uH

440uF

12V

1nF

=17.2k

×π ××

××

×π ××

××

Ω

Choose C

3=1nF, R4=17.4kΩ.

5. Calculate C

2 with zero Fz1 at 75% of the LC

double pole by equation (11).

Z14

0.75 7.6kHz 17.4k

1.6nF

×π ××

×π ×

×Ω

Choose C

2=1.5nF.

6. Calculate C

1 by equation (14) with pole Fp2 at

half the switching frequency.

17.4k

300kHz

30pF

×π ××

×π ×

Ω×

Choose C

1=33pF

7. Calculate R

3 by equation (13).

P13

60.3kHz 1nF

2.64k

×π ××

=Ω

Choose R

3=2.61kΩ.

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