Datasheet

Closing the loop B5973D
18/44 DocID14117 Rev 4
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
of the error amplifier are shown in Figure 10. R
C
and C
C
introduce a pole and a zero in the
open loop gain. C
P
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
Where A
vo
= G
m
· R
o
Figure 10. Error amplifier equivalent circuit and compensation network
A
0
s
A
V0
1s+ R
c
C
c

s
2
R
0
 C
0
C
p
+R
c
C
c
sR
0
C
c
 R
0
C
0
C
p
+R
c
C
c
++1++
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------=
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