Functional description

ST1S50

10/29

DocID025723 Rev 4

In Figure 4 is shown the simple small signal model for the peak current mode control loop.

Figure 4. Block diagram of the loop for the small signal analysis

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

1.

2.

3.

Equation 1

sense circuitry,

ESR of the output capacitor.

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

Equation 2

L

Cout

Current sense

Logic

And

Driver

Slope

Compensation

PWM comparator

Error Amp

Rc

Cc

R1

R2

0.8V

High side

Switch

Low side

Switch

VIN



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

1

1



L

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

–

 0.5

–







+

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

1

s



z

------

+





1

s



p

------

+











=



Z

1



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

=