DocID026968 Rev 2

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AST1S31HF

Functional description

33

It’s also possible define the output voltage in function of input voltage, on phase time and

switching frequency:

Equation 19

So the on phase the equation results:

Equation 20

Off phase:

Equation 21

It is possible to repeat the considerations realized to the on phase equation. So it's possible

to write the off phase equation in the following manner:

Equation 22

The peak current escalates over the peak current threshold (called “OCP1”) if :

Equation 23

In case the current escalates up to a further current threshold (called “OCP2”), slightly

higher than OCP1, the converter stops the switching activity, the reference of the error

amplifier is pulled down and then it restarts with a new soft-start procedure. If the

overcurrent condition is still active, the current foldback with frequency reduction properly

limit the output current.



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



==

I







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



–

HighSide

+

 I



–

L



=

I

TOFF

LowSide

+

 IV

OUT

–



–

L



=

I



LowSide

+

 IV

FB





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



–



–

L



=

I

 I



