Typical application

AN937

24/29

Doc ID 5655 Rev 15

Using a compensation network with R4= 15 k

Ω, C4 = 22 nF and C5 = 82 pF, the gain and

Phase Bode plots are shown in Fig. 31-32. The cut-off frequency and the phase margin are:

Fc = 36KHz

Phase margin = 62°

Fc = 34KHz

Phase margin = 70°

Fc = 18KHz

Phase margin = 92°

Fc = 14KHz

Phase margin = 88°

Fc = 11KHz

Phase margin = 83°

Fc = 8.6KHz

Phase margin = 74°

Figure 29.

Gain Bode plot open loop

F

p1

1

2

π R

o

C

c

⋅⋅

⋅

----------------------------------

1

2

π 1.2 10

6

22 10

9

–

⋅⋅

⋅

⋅

⋅

-----------------------------------------------------------------

6.029Hz

==

=

F

p2

1

2

π R

c

C

o

⋅⋅

⋅

----------------------------------

1

2

π 15 10

3

82 10

12

–

⋅⋅

⋅

⋅

⋅

------------------------------------------------------------------

125KHz

==

=

F

oLN

1

2

π R

2

C

9

⋅⋅

⋅

----------------------------------

1

2

π 2.7 10

3

4.7 10

9

–

⋅⋅

⋅

⋅

⋅

-------------------------------------------------------------------

12KHz

==

=

F

pLN

1

2

π

R

2

R

3

⋅

R

2

R

3

+

-------------------- C

9

⋅⋅

⋅

------------------------------------------------

1

2

π 1.75 10

3

4.7 10

9

–

⋅⋅

⋅

⋅

⋅

----------------------------------------------------------------------

19KHz

==

=

0.1

1

10

100

1 .10

3

1 .10

4

1 .10

5

1 .10

6

20

9

2

13

24

35

46

57

68

79

90

Vout=3.3V

Vout=5V

Vout=12V

Vout=15V

Vout=18V

Vout=24V

0 dB

Frequency [Hz]