A6902D View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
A6902D
STMicroelectronics
'A6902D' PDF : 33 Pages View PDF
7
Closing the loop
A6902D
Closing the loop
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
below. RC and CC introduce a pole and a zero in the 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:
(3)
A0 s
= AV0 ∙ s2 ∙ R0 ∙
C0 + CP
1 + s ∙ RC ∙ CC
∙ RC ∙ CC + s ∙ R0 ∙ CC + R0 ∙
C0 + CP
+ RC ∙ CC
+1
Where
(4)
AV0 = Gm ∙ R0
Figure 7. Error amplifier and compensation network
E/A
+
COMP
FB
-
Rc
Cp
Cc
V+
ΔV
GmΔV
Ro
0.8MΩ
Co
10pF
Rc
Cp
Cc
DS5503 - Rev 6
page 12/33
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