Device description

A6984

22/47

DocID030396 Rev 1

The switching activity drives the inductor voltage so the small signal transfer function can be

calculated as:

Equation 10

Equation 10 can be simplified as follows:

Equation 11

The pole splitting is guaranteed by the condition:

Equation 12

In case:

Equation 13

Equation 10 can be simplified as:

Equation 14

which represents the virtual ESR of the network in Figure 14.

H(s)

vFB(s)

iL(s)

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

s L

DCR

+





R

COT

1

sC

COT



1

1

sC

DC



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

1

1

R

2

-------

1

R

3

-------

+

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

+

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

+

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

+

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

1

sC

COT



1

1

sC

DC



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

1

1

R

2

-------

1

R

3

-------

+

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

+

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

+

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

1

1

R

2

-------

1

R

3

-------

+

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

1

sC

DC



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

1

1

R

2

-------

1

R

3

-------

+

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

+

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



==

H(s)

vFB(s)

iL(s)

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

s L

DCR

+



 s



1s

R

COT

1

1

R

2

-------

1

R

3

-------

+

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

+











C

DC



+

1s

1

1

R

2

-------

1

R

3

-------

1

R

COT

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

++

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











C

COT



+



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

C

DC

1

R

2

-------

1

R

3

-------

+

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



==

C

DC

10 C

COT





R

COT

10

1

R

2

-------

1

R

3

-------

+





f

z

1

2





-----------

L

DCR

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



=

fsw

«

f

PL

1

2

 R

COT

1

1

R

2

-------

1

R

3

-------

+

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

+

C

DC





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

=

fsw

«

f

PH

1

2



1

1

R

2

-------

1

R

3

-------

1

R

COT

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

++

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











C

COT





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

fsw

«

=

ESR

VRT

H(s)

s2

 fsw







vFB(s)

iL(s)

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





s2

 fsw







L

R

COT

C

COT



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

==

=