DocID026968 Rev 2

13/33

AST1S31HF

Functional description

33

Equation 4

where:

Equation 5

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

Equation 6

where:

Equation 7

and:

Equation 8

The resistor to adjust the output voltage gives the term from output voltage to the FB pin.

Equation 9

The transfer function from FB to Vc (output of E/A) introduces the singularities (poles and

zeroes) to stabilize the loop. In Figure 6 the small signal model of the error amplifier with the

internal compensation network is shown.



p

1



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

–

 0.5

–





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

+

=

1

------

+

=



=

–

L



=



















1

1

s





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

s

2



n

2

------

++

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

=

1

 m

C

1D

–

 0.5

–







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

=



n

 f

SW



=



+

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

=