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

9

Rev. 3.0

03/14/06

Case 1:

F

40dB/decade

20dB/decade

loop gain

LC

F

ESR

F

compensator

power stage

F

O

F

P1

F

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

F

1.Calculate the location of LC double pole F

LC

and ESR zero F

LC

OUT

OUT

1

F

2

LC

1

2

1uH

440uF

7.6kHz

=

×π ××

=

×π ××

=

ESR

OUT

1

F

2

ESRC

1

2

6m

440uF

60.3kHz

=

×π ××

=

×π ×

Ω×

=

2. Set R

×

Ω×

=

=Ω

2

REF

1

OUT

REF

RV

20k

0.8V

R =

16k

V

-V

1.8V-0.8V

Choose R

3. Set zero F

4. Calculate R

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

F

3

2

z2

p1

1

11

C =

(-)

2

R

FF

1

11

=

(

-)

2

20k

7.6kHz 60.3kHz

=916pF

×

×π×

×

×π×Ω

OSCO

4

out

in3

V

2

FL

R =C

VC

1.5V

2

50kHz 1uH

=

440uF

12V

1nF

=17.2k

×π ××

××

×π ××

××

Ω

Choose C

5. Calculate C

double pole by equation (11).

2

Z14

1

C

2

FR

1

2

0.75 7.6kHz 17.4k

1.6nF

=

×π ××

=

×π ×

×

×Ω

=

Choose C

6. Calculate C

half the switching frequency.

1

4

P2

1

C

2

RF

1

2

17.4k

300kHz

30pF

=

×π ××

=

×π ×

Ω×

=

Choose C

7. Calculate R

3

P13

1

R

2

FC

1

2

60.3kHz 1nF

2.64k

=

×π ××

=

×π ××

=Ω

Choose R