AN937

Typical application

Doc ID 5655 Rev 15

23/29

3.7

Error amplifier and compensation blocks

The open loop gain is:

where Cout is the parallel between the output and the external capacitance of the Error

Amplifier and Ro the E/A output impedance. Rc and Cc are the compensation values.

3.8

LC filter

3.9

PWM gain

where Vct is the peak to peak sawtooth oscillator.

3.10

Voltage divider and leading network

Poles and zeros value are:

As

()

gm

R

O

1s R

c

C

c

⋅⋅

+

()

⋅

s

2

R

o

C

o

R

c

C

c

sR

o

C

c

R

o

C

o

R

c

C

c

⋅

+

⋅

+

⋅

() 1

+

⋅

+

⋅⋅⋅

⋅

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

⋅

=

A

os

()

1R

esr

C

out

s

⋅⋅

+

LC

out

s

2

R

esr

s1

+

⋅

+

⋅⋅

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

=

V

CC

V

ct

-----------

V

CC

6

⋅

V

CC

1

–

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

6

≈

=

A

os

()

R

3

R

2

R

3

+

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

1R

2

C

9

⋅

+

1s

R

2

R

3

⋅

R

2

R

3

+

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

9

⋅⋅

+

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

⋅

=

F

o

1

2

πR

esr

C

out

⋅

⋅

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

1

2

π 0.130 150 10

6

–

⋅⋅

⋅

⋅

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

8.2KHz

==

=

F

p

1

2

π

LC

out

⋅

⋅⋅

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

1

2

π

120 10

6

–

150 10

6

–

⋅⋅

⋅

⋅⋅

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

1.2kHz

==

=

F

ocomp

1

2

π R

c

C

c

⋅⋅

⋅

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

1

2

π 15 10

3

22 10

9

–

⋅⋅

⋅

⋅

⋅

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

492Hz

==

=