Datasheet

AN4165 Feedback loop calculation guidelines
Doc ID 023661 Rev 1 25/37
The mathematical expression of the compensator C(f) is:
Equation 5
where (with reference to the schematic of
Figure 2 ):
Equation 6
Equation 7
Equation 8
are to be chosen with the purpose to ensure the stability of the overall system. Gm = 2 mA/V
(typical) is the VIPER26 transconductance.
11.2 Compensation procedure
The first step is to choose the pole and zero of the compensator and the crossover
frequency, for instance:
● fZc = fp/2
● fPc = fz
● fcross = fcross_sel ≤ fsw/10.
G1(fcross_sel) can be calculated from
Equation 2 and, being by definition
| C(fcross_sel)*G1(fcross_sel)| = 1, C
0
can be calculated as follows:
Equation 9
()
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛⋅
+⋅⋅⋅⋅
⋅
+
⋅=
Δ
Δ
=
fP c
jf
jf
fZc
jf
H
C
V
I
fC
COMP
12
1
0
OUT
pk
π
43
4
87
0
RR
R
CC
Gm
C
+
⋅
+
−=
772
1
CR
fZc
⋅⋅⋅
=
π
8772
87
CCR
CC
fPc
⋅⋅⋅⋅
+
=
π
)_(1
_
1
_
1_2
0
selfcrossG
H
fZc
jselfcross
fPc
jselfcross
jselfcross
C
COMP
⋅
⋅
+
⋅
+⋅⋅⋅⋅
=
π