DocID026876 Rev 1

17/39

R5973D

Closing the loop

39

7.1

Error amplifier and compensation network

The output L-C filter of a step-down converter contributes with 180 degrees phase shift in

the control loop. For this reason a compensation network between the COMP pin and

GROUND is added. The simplest compensation network together with the equivalent circuit

open loop gain. CP does not significantly affect system stability but it is useful to reduce the

noise of the COMP pin.

The transfer function of the error amplifier and its compensation network is:

Equation 2

Figure 9. Error amplifier equivalent circuit and compensation network

Equation 3

Equation 4



+









s

2



+

 R

c



+

 R

c



+



+

 1

+



+







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

=

1

2









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

=

1

2







+





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

=