ST1S40

Functional description

Doc ID 17928 Rev 4

9/30

Three main terms can be identified to obtain the loop transfer function:

1.

2.

3.

Equation 1

current sense circuitry,

the ESR of the output capacitor.

the error amplifier that introduces a double pole at one half of the switching frequency.

Equation 2

Equation 3

where:

Equation 4

avoid sub-harmonic oscillations at duty cycle over 50%.

Equation 5

where:

G

()

R

LOAD

R

i

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

1

1

R

out

T

SW

⋅

L

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

m

C

1D

–

() 0,5

–

⋅

[]

⋅

+

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

1

s

ω

z

------

+





1

s

ω

p

------

+





---------------------- F

()

⋅⋅

⋅

=

ω

Z

1

ESR C

OUT

⋅

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

=

ω

p

1

R

LOAD

C

OUT

⋅

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

m

C

1D

–

() 0,5

–

⋅

LC

OUT

f

SW

⋅⋅

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

+

=

m

C

1

S

e

S

n

------

+

=

S

e

V

pp

f

SW

⋅

=

S

n

V

IN

V

OUT

–

L

------------------------------ R

i

⋅

=

















F

()

1

1

s

ω

n

Q

P

⋅

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

s

2

ω

n

2

------

++

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

=